Volumes Available:
Volume 104, Number 1041   November 2000
Volume 107, Number 1068   February 2003
Volume 107, Number 1069   March 2003
Volume 107, Number 1071   May 2003
Volume 107, Number 1072   June 2003
Volume 107, Number 1073   July 2003
Volume 107, Number 1074   August 2003
Volume 107, Number 1075   September 2003
Volume 107, Number 1076   October 2003
Volume 107, Number 1077   November 2003
Volume 107, Number 1078   December 2003
Volume 108, Number 1079   January 2004
Volume 108, Number 1080   February 2004
Volume 108, Number 1081   March 2004
Volume 108, Number 1082   April 2004
Volume 108, Number 1083   May 2004
Volume 108, Number 1084   June 2004
Volume 108, Number 1085   July 2004
Volume 108, Number 1086   August 2004
Volume 108, Number 1087   September 2004
Volume 108, Number 1088   October 2004
Volume 108, Number 1089   November 2004
Volume 108, Number 1090   December 2004
Volume 109, Number 1091   January 2005
Volume 109, Number 1092   February 2005
Volume 109, Number 1093   March 2005
Volume 109, Number 1094   April 2005
Volume 109, Number 1095   May 2005
Volume 109, Number 1096   June 2005
Volume 109, Number 1097   July 2005
Volume 109, Number 1098   August 2005
Volume 109, Number 1100   October 2005
Volume 109, Number 1101   November 2005
Volume 109, Number 1102   December 2005
Volume 110, Number 1103   January 2006
Volume 110, Number 1104   February 2006
Volume 110, Number 1105   March 2006
Volume 110, Number 1106   April 2006
Volume 110, Number 1107   May 2006
Volume 110, Number 1108   June 2006
Volume 110, Number 1109   July 2006
Volume 110, Number 1110   August 2006
Volume 110, Number 1111   September 2006
Volume 110, Number 1112   October 2006
Volume 110, Number 1113   November 2006
Volume 110, Number 1114   December 2006
Volume 111, Number 1115   January 2007
Volume 111, Number 1116   February 2007
Volume 111, Number 1117   March 2007
Volume 111, Number 1118   April 2007
Volume 111, Number 1119   May 2007
Volume 111, Number 1120   June 2007
Volume 111, Number 1121   July 2007
Volume 111, Number 1122   August 2007
Volume 111, Number 1123   September 2007
Volume 111, Number 1124   October 2007
Volume 111, Number 1125   November 2007
Volume 111, Number 1126   December 2007
Volume 112, Number 1127   January 2008
Volume 112, Number 1128   February 2008
Volume 112, Number 1129   March 2008
Volume 112, Number 1130   April 2008
Volume 112, Number 1131   May 2008
Volume 112, Number 1132   June 2008
Volume 112, Number 1133   July 2008
Volume 112, Number 1134   August 2008
Volume 112, Number 1135   September 2008
Volume 112, Number 1136   October 2008
Volume 112, Number 1137   November 2008
Volume 112, Number 1138   December 2008
Volume 113, Number 1139   January 2009
Volume 113, Number 1140   February 2009
Volume 113, Number 1141   March 2009
Volume 113, Number 1142   April 2009
Volume 113, Number 1143   May 2009
Volume 113, Number 1144   June 2009
Volume 113, Number 1145   July 2009
Volume 113, Number 1146   August 2009
Volume 113, Number 1147   September 2009
Volume 113, Number 1148   October 2009
Volume 113, Number 1149   November 2009
Volume 113, Number 1150   December 2009
Volume 114, Number 1151   January 2010
Volume 114, Number 1152   February 2010
Volume 114, Number 1153   March 2010
Volume 114, Number 1154   April 2010
Volume 114, Number 1155   May 2010
Volume 114, Number 1156   June 2010
Volume 114, Number 1157   July 2010
Volume 114, Number 1158   August 2010

Volume 104, Number 1041   November 2000

Planning for super safety the fail-safe dimension

Authors
R. W. Howard

Abstract
It has long been a requirement in air transport that no single failure can have a catastrophic effect. As nothing can ever be failure free, fail-safety in design and operation must be provided in all respects. This paper explores the design background, application and history of the concept of fail-safety in air transport and the vital role it plays in overall safety. It is suggested that fail-safety is the most important discipline of all those involved in safety in design and operations. Without it, the current air transport safety levels, even using the latest technologies, would not be possible. In the modern air transport system, all accidents are due either to fail-safety implementations breaking down, or not having been adequately provided, or due to extremely remote multiple coincident failures. It can be argued that inadequacies in fail-safety provisions at the very low target failure rates now demanded, is the main reason for the near constancy of the accident rate, and the consequent increase in numbers of accidents as the world fleet grows. In the forefront of fail-safety problems is the inadequacy of its use in the management operations of crew in the modern air transport cockpit.

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Volume 107, Number 1068   February 2003

Flocking of autonomous unmanned air vehicles

Authors
B. Crowther
School of Engineering, University of Manchester, UK

Abstract
The use of large numbers of unmanned air vehicles in a given air space presents a challenge for conventional air traffic control methods. Flocking (or schooling, swarming or herding) in nature arises when mobile organisms find benefit in living at high densities. The present paper applies rules of flocking (cohesion, alignment, separation, and migration) to the problem of managing the flight of a number of autonomous unmanned air vehicles. A six-degree of freedom aerodynamic model of an existing UAV is used to simulate the flocking flight vehicles. It is found that application of the cohesion and alignment rules is sufficient to generate true flocking behaviour in that the flight vehicle density is increased and the flock members converge on a common heading.

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Volume 107, Number 1068   February 2003

The human-machine partnership in UCAV operations

Authors
A.D. White
QinetiQ, Cody Technology Park, Farnborough, UK

Abstract
At a time when a great deal of research on UCAVs is aimed at max-imising their autonomy it should not be forgotten that human opera-tors will, ultimately, remain in control to some degree. The decision sharing relationship between the operator and the UCAV depends on political constraints as well as the intelligence of the UCAV system. This in turn dictates the amount and type of information to be exchanged and the way in which it is communicated with the operator. Operational flexibility is a key military driver and in order to achieve it, a variable autonomy command interface, combined with information fusion and intelligent decision-support systems, will be required. To be effective the operator will need to work in concert with the UCAV system rather than act simply as a command source and an information sink. The implications of this partnership for command and monitoring requirements and in particular for weapons release authorisation, are discussed in this paper.

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Volume 107, Number 1069   March 2003

A non-traditional look at safety

Authors
M. Gallagher and J.L. Foster
Federal Aviation Administration, Small Airplane Directorate

Abstract
Our role includes studying and understanding the causes of accidents. The GA community has collected a large volume of safety data based on service history. Review of these data (through programs like the FAA Administrators Safer Skies Initiative) has highlighted several key areas where we can improve safety. Complimentary to the data review processes, the SAD has taken a critical look at how we do business and interface with owners and operators. Our self-evaluation has led us to new approaches in our approval process. This paper outlines changes taking place in the FAA and the efforts that we are making to reduce the number of accidents in the current fleet and improve our effectiveness in working with industry, operators, and owners to field a new generation of equipment and aeroplane.

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Volume 107, Number 1069   March 2003

Mechanical and electromagnetic behaviour of auxetic honeycomb structures

Authors
F. Scarpa, F.C. Smith and B. Chambers
University of Sheffield, UK
G. Burriesci
University of Palermo, Italy

Abstract
In this work a combined analysis of the out-of-plane mechanical and the electromagnetic properties of auxetic re-entrant honeycombs is performed. Experimental and numerical simulations are carried out to evaluate the correlation between the anisotropicity of the transverse mechanical properties (shear and compressive modulus) and the permittivity tensor of auxetic honeycombs. The results are evaluated to assess the feasibility of this kind of cellular solid for electromagnetic absorption and window applications with high structural integrity performance.

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Volume 107, Number 1069   March 2003

Study of unsteady characteristics of flare induced hypersonic shock-wave boundary layer interaction flowfield with variation in γ

Authors
S. B. Verma
DLR Lampoldshausen, germany

Abstract
Experimental work has been carried out to study the unsteady flowfield characteristics related to shockwave/boundary-layer interaction. Tests were carried out on an axisymmetric configuration that has a semi-cone angle of 35° and a flare angle of 20°. Further influence of low γ gases (CO2 and CF4 ) on the overall interaction process is also investigated. Both surface and off-surface analysis has been carried out. Off-surface study has been made with a laser schlieren system. The purpose of this study was to investigate the source of the unsteadiness related to such interactions. Two types of shock motions, namely, flapping and rippling could be identified for air, the relative importance of each of which is strongly dependent on the location within the interaction and on the type of test gas.

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Volume 107, Number 1071   May 2003

Smart Spring identification for hovering rotor aeroelastic-stability augmentation

Authors
M. Gennaretti, L. Poloni, F. Nitzche

Abstract
This work deals with tailoring of adaptive material included at the roots of hingeless helicopter rotor blades to be used in individual blade control (IBC) strategies. Usually, IBC strategies involving the use of adaptive materials either consider adaptive material embedded in the blade structure for inducing strain deformations, or apply adaptive actuators for controlling segments of the blade (e.g. for moving trailing-edge flaps). Here, the adaptive material is used to provide augmentation of modal damping in a passive control approach, that can be conveniently tuned so as to make it the most suitable for the actual rotor configuration under examination. The presentation of a procedure for tailoring this smart spring is the aim of the paper.

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Volume 107, Number 1071   May 2003

Turbulent mixing layer from two non-parallel streams

Authors
M A Azim & A K M S Islam
Dept of Mech Engineering, Banglaesh University of Engineering & Technology, Dhaka, Bangladesh

Abstract
An experimental investigation has been conducted on the mixing layers produced from the merging of two non-parallel streams. To study the effect of velocity ratio on its development, mixing layers were produced with velocity ratios 0.7, 0.8 and 0. 9. The boundary layers were untripped and initially turbulent in all the cases. For each velocity ratio, measurements were made at six streamwise locations. It was found that for velocity ratios 0.7 and 0.8, mixing layers appear to attain self-similarity but failed for 0. 9 within the measurement domain. The development distance of the mixing layer flow was increased with increasing velocity ratio and the splitter wake was found to play an important role in its development. The mixing layer growth was found to decrease with increasing velocity ratio though the spread of the layer was larger at the high speed side.

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Volume 107, Number 1071   May 2003

Physical modelling of a flight control system

Authors
S. Sadovnychiy
Mexican Petroleum Institute, Mexico City, Mexico

Abstract
This paper deals with the methods of physical modelling of Flight Control Systems (FCS) by means of Dynamically Similar free-flying Models (DSM) for the investigation of stability and controllability of aircraft at subsonic flight speeds. The subsonic flight regime allows us to avoid Mach number similarity considerations. The large scale of the DSM meets autosimilarity of Reynolds numbers, whilst Froude similarity is assured during the development and manufacturing of the DSM. This paper proves the presence of necessary and sufficient conditions of similarity for the FCS of an aircraft, and that of its DSM. The existence of necessary conditions have been proved both mathematically (by means of the π−Theorem from the theory of dimensions), and with equations involving physical quantities.

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Volume 107, Number 1071   May 2003

Robustness of the subsonic doublet lattice method

Authors
L H van Zyl
Defence Aeronautics Programme, CSIR, Pretoria, South AFrica

Abstract
The subsonic doublet lattice method (DLM) has been the industry standard method for the calculation of unsteady air loads for the past three decades. A recent comparison between the DLM and the subsonic constant pressure panel code ZONA6 suggested that the DLM lacked robustness. However, the DLM code used in the comparison was flawed and not representative of the DLM as such. Results from a contemporary DLM code are presented for the same test cases that were used in the misleading comparison. These new results show that the DLM can produce valid results for all the test cases considered. Where feasible, a comparison is made between results from the present DLM code and the published ZONA6 results.

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Volume 107, Number 1072   June 2003

The air side of future warfare - military aeronautics

Authors
D.M. Bushnell
Chief Scientist, NASA Langley Research Center

Abstract
The ongoing revolutions in information, biological, energetics and nano technologies are changing the nature and equipment of warfare. This is particularly true in military aeronautics. In the nearer term aircraft are becoming increasingly uninhabited enabled by the IT revolution, with multitudinous accompanying benefits in terms of afford-ability, survivability, redefinition of risk and lethality. THE issue for such aircraft is enhanced persistence and increased range within the context of the overall system metrics. In the longer term the increasingly capable worldwide sensor web will place at risk all air vehicles, in or out of theatre and whether or not they are stealthy. This, combined with advanced conventional weapons, high energy density material powered EMP weapons and affordable swarms of brilliant munitions will probably require yet another re-definition of military aeronautics, perhaps as survivable (hardened) hypersonic, global range, boost-glide devices.

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Volume 107, Number 1072   June 2003

Aero engines of the future

Authors
P.C. Rufffles
Rolls-Royce, Derby, UK

Abstract
This paper will examine both the civil and defence aerospace sectors and open up the debate by highlighting the key factors influencing the future direction in these markets.It will address the likely requirements for aircraft propulsion systems in the near,medium and longer-term,together with the underpinning technologies that are likely to prove essential in delivering the propulsion systems that the community and the customer demand.

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Volume 107, Number 1072   June 2003

The role of CFD in aerodynamics, off-design

Authors
P.R. Spalart and D.R. Bogue
Boeing Commercial Airplanes, Seattle, USA

Abstract
We discuss the status, trends and long-term ambitions of Computational Fluid Dynamics (CFD) when applied away from the design point or concept, and therefore in the historically weak areas of CFD. This includes both undesirable flight conditions, such as stall, and undesirable products of the flow, such as noise. All pose the great challenge of turbulence, and accuracy is as dependent on the ideas behind the turbulence treatment as it is on computing power. A measured shift from Reynolds-averaged representations to large-eddy simulations will take place. Empiricism, both turbulence and engineering related, will recede only step by step over many years. Yet, CFD will make full use of every increase in computer power of this century. Increasingly, CFD will compete with flight tests, not just with wind tunnels, and will be validated by flight tests. Integration with other disciplines will allow us to predict crucial phenomena such as flutter, sonic fatigue, and pilot-induced oscillations.

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Volume 107, Number 1072   June 2003

Materials for airframes

Authors
H.M. Flower
Dept of Materials, Imperial College, London UK
C. Soutis
Dept of Aeronautics, Aerospace Engineering, University of Sheffield, Sheffield UK

Abstract
The prediction of the future is always a relatively uncertain process. The only certain fact is that the prediction is unlikely to be wholly accurate. Even the prediction of trends following examination of past performance will be uncertain regarding the future rate of advance and may be entirely upset by new discoveries and their application. This is as true for examining the future of airframe materials as it is for prediction of economic growth, which itself significantly affects the development of materials technology in the aircraft industry. However, 100 years of powered manned flight does give a solid database from which to begin. In that period airframes have moved from wood, wire and canvas, through to riveted and stressed skin metal structures to adhesively bonded polymer composites. In each case the use of new materials is associated with a change in fabrication methods and it may be confidently anticipated that this will remain true in the future.

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Volume 107, Number 1072   June 2003

Aircraft Structures in the centuries ahead

Authors
A. Beukers, M. van Tooren and C. Vermeeren
Faculty of Aerospace Engineering, Delft University of Technology

Abstract
The first centennial of man’s first powered flight, which was performed by Wilbur (1867-1912) and Orville (1871-1948) Wright will be celebrated in 2003. These brothers’ unique and trend-setting enterprise, their skills to develop, build and commercialise controllable and load-carrying flying machines, formed the first example of a private interdisciplinary aerospace development and design initiative. It was at the same time a rare example of entrepreneurial engineering. Their work involved wind-tunnel testing of lifting devices and full-scale tests of major structural components. Equally if not more importantly they developed an essential propulsion system consisting of a lightweight 36hp engine with four cylinders in line and a fuel injected carburettor. This engine propelled two pusher propellers through a drive system of chains. Moreover they developed the systems to control their flight.

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Volume 107, Number 1072   June 2003

Systems and avionics

Authors
P.H. Collins and B.L. Perry
London, UK

Abstract
This paper looks to future developments and concepts in Systems and Avionics. One hundred years ago neither avionics nor even systems would have been recognised as having a place in aeronautics. The concept of aircraft systems developed, as the complexity of each element of the aircraft grew, requiring specialism in the design, operation and maintenance of those elements. Early examples would have been the propulsion and flying controls systems. By the 1930s passenger aircraft might have carried, in addition to the pilots, a navigator, flight engineer and radio operator, each responsible for his own collection of systems, with the aircraft itself probably having an embryonic electrical system.

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Volume 107, Number 1072   June 2003

Simulation - the real world of the future!

Authors
R.A. Curnutt
The Boeing Company, Seattle, Washington, USA

Abstract
Flight simulation has definitely kept pace with powered flight through the past century, and its future is seemingly unlimited. To understand where the future might lie, it is important to consider the current situation, in terms of training, engineering and entertainment industry (consumer) uses of simulation. As will be shown, simulation has become a critical tool for use in aircraft design and validation, as well as playing a key and well-known role in flight training. Of course, entertainment uses of simulation are becoming more common; ranging from PC-based games to rides at the mall. By reflecting on these uses of simulation and the drivers behind them, it is possible to project into the future; both near-term, and well into the next 100 years. The projections will hopefully lead to healthy discussion and further speculation in academic and industry forums – and ultimately to new and better ideas.

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Volume 107, Number 1072   June 2003

Civil Aviation & the environmental challenge

Authors
J.E. Green
Aircraft Research Association, Bedford, UK

Abstract
In the coming century, the impact of air travel on the environment will become an increasingly powerful influence on aircraft design. Unless the impact per passenger kilometre can be reduced substantially relative to today’s levels, environmental factors will increasingly limit the expansion of air travel and the social benefit that it brings. This essay considers the three main impacts, noise, air pollution around airports and influence on climate change. Of the three, impact on climate change is taken to have the greatest long-term importance and is discussed at the greatest length. It is argued that, of the three main contributors to climate change from aircraft – CO 2 emissions, NO X emissions and the creation of persistent contrails – it is the last two which are the most promising targets. Ways of reducing the impacts of these two are discussed and it is noted that, in each case, the best environmental result is likely to entail some increase in CO 2 emissions.

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Volume 107, Number 1072   June 2003

The future of rotorcraft

Authors
G.M. Byham
Head of Engineering, AgustaWestland, Yeovil UK

Abstract
In writing this essay on rotorcraft I have chosen to confine my interests to the flying machines themselves, their development and the pressures that are shaping their future. The few paragraphs that record the early days of rotary wing flight are a small precis of far more detailed published works that plot the history and personalities involved in bringing helicopters to the market place. In the Centenary Journal of the Royal Aeronautical Society, published in 1966, Raoul Hafner contributed a chapter on British Rotorcraft. Hafner’s paper bears the hallmark of being a personal memoir from one who was actually there, finding the fundamental solutions to helicopter engineering problems and seeing them continue to be used as part of the basic fabric of our technology today. Others have gathered the historical evidence and offer it to us in an orderly manner to mark the path that our technical field has followed.

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Volume 107, Number 1072   June 2003

Light Aviation - past, present and future

Authors
A.C. Welch

Abstract
Light aviation was the name given to amateur flying in the 1920s, to distinguish it from military and commercial aviation. It is still the valuable entry into aviation generally, as it is a relatively inexpensive way to try out new ideas. But to fulfil its potential it has to remain attractive and affordable, particularly to the young. This paper endeavours to speculate how light aviation will fare during aviations second century in Britain – or at least for the next 20-30 years, in an increasingly complex world in which global accessibility is commonplace.

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Volume 107, Number 1073   July 2003

Velocity field path-planning for single and mutiple unmanned aerial vehicles

Authors
C.R. McInnes
dept of Mechanical Engineering, University of Glasgow, Glasgow, UK

Abstract
Unmanned aerial vehicles (UAV) have seen a rapid growth in utilisation for reconnaissance, mostly using single UAVs. However, future utilisation of UAVs for applications such as bistatic synthetic aperture radar and stereoscopic imaging, will require the use of multiple UAVs acting cooperatively to achieve mission goals. In addition, to de-skill the operation of UAVs for certain applications will require the migration of path-planning functions from the ground to the UAV. This paper details a computationally efficient algorithm to enable path-planning for single UAVs and to form and re-form UAV formations with active collision avoidance. The algorithm presented extends classical potential field methods used in other domains for the UAV path-planning problem. It is demonstrated that a range of tasks can be executed autonomously, allowing high level tasking of single and multiple UAVs in formation, with the formation commanded as a single entity.

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Volume 107, Number 1073   July 2003

Aerodynamic admittance of a two-dimensional body

Authors
A. Filippone
Dept of Mechanical ENgineering, UMIST, Manchester, UK
J. Siquier
Ecole Polytechnique, Palaiseau, France

Abstract
The unsteady load response in the frequency domain for a general two-dimensional body has been determined. Systems with one degree of freedom have been considered. The theory is based on the potential incompressible flow, and resolves around a mathematical treatment that starts from the theory of Drischler and Diederich. Admittance for the lift force and pitching moment (or side force and yawing moment for non lifting systems) has been calculated in closed form or numerically for aerofoils, swept back and swept forward wings, delta wings, and some ground vehicles (various car shapes) using sinusoidal and square gusts. Simulations have been performed for a wide range of gust speed ratios. The general features of the admittance function are discussed. It is proved that for some geometries there is an large number of frequencies that yield critical damping. These frequencies are generally very high. Comparisons with existing experimental data are good in the whole range of practical frequencies.

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Volume 107, Number 1073   July 2003

A study of synthetic jets from rectangular and dual-circular orifices

Authors
M. Watson, A.J. Jaworski and N.J. Wood
Fluid Mechanics Research Group, University of Manchester, UK

Abstract
The results of an investigation into the effect of both the number of orifices and the geometry of these orifices on the fluid structures exiting from a synthetic jet actuator are presented. The experiments have used smoke and laser visualisation and single hotwire measurement techniques to establish the flow field exiting the various orifices and the fluid velocities in the exit plane of the orifice. The results indicate that the use of two small orifices can perhaps produce two coherent vortex rings with a total circulation greater than that found in the ring produced by a large, single orifice of equivalent area. However, they have also shown that there are three different types of interaction between two adjacent orifices, related to the spacing between them and the level of excitation applied to the diaphragm. In addition, these interactions may affect the overall level of circulation in different ways.

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Volume 107, Number 1073   July 2003

Heat transfer and flow behind a step in high enthalpy superorbital flow

Authors
M.J.Hayne, D.J. Mee, R.G. Morgan & T.J. McIntyre
Centre for Hypersonics, University of Queensland, Brisbane, Australia
S.L. Gai
School of Aerospace & Mec Engineering, University College, UNSW@ADFA, Canberra, Australia

Abstract
Heat transfer levels have been investigated behind a rearward-facing step in a superorbital expansion tube. The heat transfer was measured along a flat plate and behind 2 and 3mm steps with the same length to step height ratio. Results were obtained with air as the test gas at speeds of 6.76kms­­­¯¹ and 9.60kms¯¹ corresponding to stagnation enthalpies of 26MJ/kg and 48MJ/kg respectively. A laminar boundary layer was established on the flat plate and measured heat transfer levels were consistent with classical empirical correlations. In the case of flow behind a step, the measurements showed a gradual rise in heat transfer from the rear of the step to a plateau several step heights downstream for both flow conditions.

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Volume 107, Number 1073   July 2003

Corner speed versus optimum turn speed

Authors
A. Kutschera & P.M. Render
Dept of Aeronautical & Automotive Engineering, Loughborough University, UK

Abstract
Work has been carried out by Kutschera (1-4) on how to assess, at the conceptual design stage, the performance of fighter aircraft. As part of this work, Kutschera (4) reviewed a number of existing and proposed metrics for assessing aircraft performance. Reference 4 also describes how the performance of an aircraft can be quantified by three types of metric. The first type are steady state or point performance metrics, such as turn rate plots and energy manoeuvrability diagrams. The second type are manoeuvrability metrics and the last are agility metrics. Agility metrics can be ruled out at the conceptual design stage because they require complex aircraft models, and the necessary information is unlikely to be available. Kutschera also showed that the more traditional approach of using performance metrics fail to give an accurate picture of the aircrafts performance over time as combat unfolds.

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Volume 107, Number 1073   July 2003

Breaking the chain
Returning Concorde to service following the Paris accident - July 2000

Authors
J.A. Jupp & J.R. Britton
Airbus, Filton, UK

Abstract
This is the story of restoring Concordes level of safety and the return of its Certificates, prior to Return to Service with British Airways and Air France. Many of the illustrations and charts in this paper are those used in the formal discussions during the return to service campaign.

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Volume 107, Number 1074   August 2003

Autonomous behavioural algorithm for space applications

Authors
G. Radice & C.R. McInnes

Abstract
The purpose of this paper is to present a new approach in the concept and implementation of autonomy for autonomous spacecraft. The one true ‘artificial agent’ approach to autonomy requires the spacecraft to interact in a direct manner with the environment through the use of sensors and actuators. Rather than using complex world models, the spacecraft is allowed to exploit the dynamics of its environment for cues as to appropriate actions to take to achieve its mission goals. The particular artificial agent implementation used here has been inspired by studies of biological systems. The so-called ‘cue-deficit’ action selection algorithm considers the spacecraft to be a non-linear dynamical system with a number of observable states. Using optimal control theory a set of rules is derived which determine which of a finite repertoire of behaviours the spacecraft will perform. A simple model of a single imaging spacecraft in low polar Earth orbit is used to demonstrate the algorithm.

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Volume 107, Number 1074   August 2003

Low cost Mercury orbiter and sample return missions using solar sail propulsion

Authors
C.R. McInnes, G. Hughes & M. MacDonald

Abstract
The use of solar sail propulsion is investigated for both Mercury orbiter (MO) and Mercury sample return missions (MeSR). It will be demonstrated that solar sail propulsion can significantly reduce launch mass and enhance payload mass fractions for MO missions, while MeSR missions are enabled, again with a relatively low launch mass. Previous investigations of MeSR type missions using solar electric propulsion have identified a requirement for an Ariane V launcher to deliver a lander and sample return vehicle. The analysis presented in this paper demonstrates that, in principle, a MeSR mission can be enabled using a single Soyuz-Fregat launch vehicle, leading to significant reductions in launch mass and mission costs. Similarly, it will be demonstrated that the full payload of the ESA Bepi Colombo orbiter mission can be delivered to Mercury using a Soyuz-Fregat launch vehicle, rather than Ariane V, again leading to a reduction in mission costs.

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Volume 107, Number 1074   August 2003

A numerical study of hypersonic laminar film cooling

Authors
X. Yang, K.J. Badcock & B.E. Richards

Abstract
A computational study has been performed to investigate the effectiveness of film cooling in hypersonic laminar flows. Both the primary and the coolant flow are air. First, three different primary flow conditions are used for validation. A uniform boundary condition at the slot exit is found to give unrealistic predictions of the heat transfer rate, whilst a boundary condition involving extended coolant inlet gives improvement. Then five coolant injection rates and three slot heights are examined. It is confirmed that increasing the coolant injection rate can increase the film cooling effectiveness for laminar cases. But slot height does not play an important role under the flow conditions in this study. The computational results are compared with the experimental results and good agreement is achieved.

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Volume 107, Number 1074   August 2003

Pilot modelling and inverse simulation for initial handling qualities assessment

Authors
N. Cameron, D.G. Thomson & D.J. Murray-Smith

Abstract
This paper describes the development of an approach to handling qualities investigation that can be applied at an early stage in the design of the vehicle. It makes use of inverse simulation techniques, together with a pilot model to provide an integrated description of the man-machine control system. In order to incorporate pilot effects into data generated by inverse simulation, the output from an inverse simulation run is applied as input to a closed-loop system model that includes the vehicle dynamics and a simple parametric model of the pilot. Parameters of the pilot model are determined by optimisation and the pilot effect is added to the system output. Validation of the approach is achieved through a case study involving a predefined mission task involving a lateral manoeuvre. Equalisation characteristics estimated for each pilot are compared with those found by inverse simulation for the same manoeuvre.

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Volume 107, Number 1074   August 2003

Buckling interaction in regular arrays of distorted hexagonal plates

Authors
C.B. York

Abstract
Linear elastic buckling strength assessments are presented for a range of thin plate arrays with optimal strength to weight ratio configurations subject to a range of arbitrary in-plane stress states. The outcomes of the assessment are presented as design curves demonstrating relative buckling strength increases with respect to the classical square plate datum of equal mass. A stiffness matrix method is adopted for the initial buckling strength predictions. The method is based on exact flat plate theory and assumes that the plate is continuous over supports, whereby deformations in one cell of the plate array influence the deformations in adjacent cells. The supporting webs of each cell are approximated in this study by simple rigid supports that enforce nodal lines or lines of zero out-of-plane displacement in the buckled panel, i.e. the bending and torsional stiffness provided by the supporting webs of the real structure are ignored. Selected results are validated by FEM prediction.

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Volume 107, Number 1075   September 2003

Flight simulation in academia - HELIFLIGHT in its first year of operation at the University of Liverpool

Authors
G.D. Padfield & M.D. White

Abstract
The challenges of helicopter simulation are being tackled across a broad front as technology is developed to meet the needs of Industry. Traditionally, the strongest impetus has come from the training community and this is likely to continue for some time as simulation technology advances at increasing pace, raising fidelity standards. The development of PC-based simulation technologies is providing a significant spur in this development and lowering the cost, making complete simulation systems of reasonably high fidelity available to smaller organisations. This paper describes the first year of operation with such a system at the University of Liverpool – HELIFLIGHT. With its full motion, wide field-of-view visuals, programmable force-feel system and the comprehensive FLIGHTLAB modelling environment, we describe the HELIFLIGHT system as high fidelity and the first year of utilisation saw extensive use in a variety of handling qualities and pilot-vehicle technology research and teaching.

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Volume 107, Number 1075   September 2003

Aerofoil at low speeds with gurney flaps

Authors
L Brown & A Fillipone

Abstract
This paper reviews the research on Gurney flaps and related high lift trailing edge devices. It investigates aerofoil performances at Reynolds numbers and below, both with the clean configuration and various Gurney flap sizes. The device height is optimised, and a semi-empirical formula linking flap height to free stream speed and aerofoil chord is proposed. The analysis shows that the optimal size of the device is always below the boundary-layer thickness at the trailing edge. Discussion of results includes analysis of hysteresis loops occurring in the L/D performances. These are mostly due to large changes in drag and small changes in lift, which occur when the aerofoil is restored to the reference angle of attack.

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Volume 107, Number 1075   September 2003

The broad delta airliner

Authors
R M Denning, J E Allen & F W Armstrong

Abstract
Aeronautics faces new and increased challenges in the 21st century. These include climate change, long-term fuel supply, traffic congestion, and noise pollution. Radical technological steps will be demanded of the industry in order to maintain a sustainable transportation system. In setting out its ideas for a Sonic Cruiser, Boeing has recently acknowledged that there is a need to look beyond the high-aspectratio wing with separate fuselage and podded engine configuration, which it pioneered at the start of the Jet era. This paper sets out the case for the broad delta including its advantages as a basis for achieving higher transonic cruising speeds, with very long range and large payloads, while providing progressive and significantly improved environmental impact. The work is based on concept designs drawing on flight and weight data from the Vulcan bomber and the Concorde aircraft – both pioneering designs, by no means at the end of their technical potential.

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Volume 107, Number 1075   September 2003

Curve fitting approach for transonic flutter prediction

Authors
A Sedaghat, J E Cooper, J R Wright & A Y T Leung

Abstract
This paper outlines an initial investigation for determining nonlinear aerodynamics for unsteady transonic flows through the use of curve fitting unsteady computational fluid dynamics (CFD) data. The full aerodynamics including linear and non-linear aerodynamics can be identified as a polynomial function. Through the curve fitting method, the important non-linear terms can be identified and the smaller terms can be neglected. Having modelled the non-linear aerodynamics and included into the aeroelastic model, the characteristics and stability of non-linear aeroelastic system can then be investigated using normal form theory. The methodology is demonstrated upon a simple two-degrees-of-freedom aeroelastic wing model with structural and aerodynamics nonlinearity. A good agreement is obtained for all cases studied between analytical and simulation results.

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Volume 107, Number 1076   October 2003

A flight test to demonstrate flutter and evaluate the flutterometer

Authors
R Lind, D F Voracek, R Truax, T Doyle, S Potter & M Brenner

Abstract
A project was recently completed that investigated the ability to predict the onset of flutter using tools like the flutterometer. This project used an experiment called the aerostructures test wing that was flown while mounted to the flight test fixture on an F-15. Several flight tests were conducted to expand the envelope and determine the aeroelastic dynamics of the experiment. The final flight ended with destruction of the experiment due to the onset of flutter. The flutterometer attempted to predict this onset by analysing the flight data. The results indicate the flutterometer is able to generate a conservative estimate of the flight conditions associated with flutter. This paper details the flight tests of the experiment and the resulting predictions from the flutterometer.

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Volume 107, Number 1076   October 2003

Future air traffic management: strategy and control philosophy

Authors
P Brooker

Abstract
The aim is to explore the philosophy of air traffic management with different strategic visions of the future: to answer the key question: ‘Who is to prevent mid-air collisions and how are they to accomplish this?’ The best strategic vision may just be the one that has the best match with the consensus on the desired strategic direction. Nevertheless, it must satisfy the main safety, financial, human performance etc. constraints. To explore the question, a blend of concepts from a range of disciplines has been used. These include risk analysis, financial decision-making, ‘cognitive engineering’ research and simple cybernetics. ‘full delegation’ – with pilots being responsible for all the tasks related to separation assurance – appears to meet most of the constraints. Some important issues for safety analyses of full delegation are sketched. Research into the nature and rate of future conflicts in a full delegation environment, using models of error processes, is crucial.

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Volume 107, Number 1076   October 2003

A dynamically fuzzy gain - scheduled design for missile autopilot

Authors
C-L Lin & C-L Hwang

Abstract
A dynamic backpropagation training algorithm for an adaptive fuzzy gain scheduling feedback control scheme with the application to missile autopilots is developed. This novel design methodology uses a Takagi-Sugeno fuzzy system to represent the fuzzy relationship between the scheduling variables and controller parameters. Mach number and angle-of-attack are used as measured, time-varying exogenous scheduling variables injected into the control law. By incorporating scheduling parameter variation information, the adaptation law for controller parameters is derived. Results from extensive simulation studies show that the presented approach offers satisfactory controlled system performance.

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Volume 107, Number 1076   October 2003

Optimisation of noise abatement arrival trajectories

Authors
H G Visser & R A A Wijnen

Abstract
This paper describes an optimisation study concerning arrival trajectories that has been conducted using a recently developed tool for the analysis and design of noise abatement procedures around airports. This new tool combines a noise model, a geographic information system, and a dynamic trajectory optimisation algorithm. The optimisation algorithm generates routings and flight-paths that minimise the noise impact in the residential communities surrounding the airport, while satisfying all imposed operational and safety constraints. The study on arrival trajectories presented herein complements an earlier study involving departure trajectories. Although the numerical results shown pertain to a particular example airport, viz Amsterdam Airport Schiphol, the study actually focuses on the development of a generic methodology that could be applied to any given airport. The results clearly demonstrate the effectiveness and flexibility of the developed tool.

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Volume 107, Number 1076   October 2003

Effects of sweep on the dynamics of active separation control

Authors
L G Pack & A Seifert

Abstract
A series of active flow control experiments were recently conducted at high Reynolds numbers on a wall mounted ‘Hump’. The model simulates the upper surface of a 20% thick Glauert-Goldschmied type airfoil at zero incidence. The flow over the model is turbulent since the tunnel sidewall boundary-layer flows over it, eliminating laminar-turbulent transition from the problem. The main motivation for the experiments was to generate a comprehensive data base for validation of unsteady numerical simulation as a first step in the development of a design tool, without which it would not be possible to effectively utilise the great potential of unsteady flow control. This paper focuses on the dynamics of several key features of the baseline as well as the controlled two- and three-dimensional flows.

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Volume 107, Number 1076   October 2003

Flight simulation - viability versus liability, issues of accuracy, data and validation

Authors
J Rolfe & B P Hampson

Abstract
Flight simulation has become an indispensable tool for aviation training. Important decisions relating to the acquisition and certification of aircrew proficiency are made based on performance in simulated flight conditions. Such a high dependency on simulation can invite questions about the validity of the assumptions on which their employment is founded. If these should be shown to be in any way deficient, those who consider that they have suffered as a result may seek redress. The paper considers the possibility that such conditions could arise and require those involved in the design, manufacture, regulation and operation of flight simulators to justify their decisions. The paper suggests that the culture should be one which acknowledges that simulation has its limitations and, consequently, exercises a duty of care for those who undertake training and assessment in flight simulators.

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Volume 107, Number 1077   November 2003

Aerospace applications of luminescent paint. Part Two: Heat transfer measurement

Authors
J R Kingsley-Rowe, G D Lock & A G Davies

Abstract
A heat transfer measurement technique has been developed, which utilised a laser to heat a spot of the ‘standard’ luminescent paint on an insulated metal wind tunnel model. The convective heat transfer coefficient was determined from the experimental quasi steady-state surface temperature, and solutions obtained from radial and axial conduction in a numerical heat transfer model. The convective heat transfer coefficient variation over both a flat plate and a NACA 0012 aerofoil have been measured in transonic flow. Measurements obtained from the flat plate were seen to agree well with correlation data from the literature. Measurements on the NACA 0012 aerofoil indicated the point of transition from laminar to turbulent boundary layer as well as the location of shock boundary layer interaction. The luminescent paint provided simultaneous measurements of pressure and temperature (see Part 1).

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Volume 107, Number 1077   November 2003

Reduction of helicopter vibration through cyclic control of variable orifice dampers

Authors
P Anusonti-Inthra, F Gandghi & L Miller

Abstract
The present study demonstrates that cyclically varying the damping coefficient of controllable lag and flap dampers can reduce the 4/rev vibratory hub loads of a four-bladed hingeless rotor helicopter in high speed forward flight. Gradient-based optimization is used to determine the optimal multi-cyclic damping variation inputs that minimise a composite vibration index comprising of all six components of vibratory hub loads. Optimal 2/rev and 3/rev variations in the lag damping coefficient virtually eliminate the vibratory hub drag force and yawing moments, and produce small reductions in the vibratory hub side force. The optimal lag damping variations, interestingly, produce increases in the 3/rev and 5/rev components of the blade root drag shear, that cancel the contributions of the blade root radial shear to the vibratory in-plane hub forces.

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Volume 107, Number 1077   November 2003

Non-linearities in flight control systems

Authors
C Fielding & P K Flux

Abstract
Non-linear behaviour is usually undesirable for the operation of any system and it needs to be minimised in flight control systems in order to provide the pilot with a predictable and well-behaved aircraft. The non-linear response characteristics exhibited by all aircraft and their flight control systems can be characterised by using nonlinear functions to simulate and analyse their behaviour. This paper explores the types of physical non-linearities that exist in aircraft flight control systems and provides some examples. It describes how the non-linear stability might be analysed and addresses the subject of actuation systems modelling. The final section provides recommendations for minimising non-linear behaviour and gives some general guidelines on how to deal with non-linear characteristics.

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Volume 107, Number 1077   November 2003

Time-linearised transonic computations including entropy, vorticity and shock wave motion effects

Authors
E Ly & J Nakamichi

Abstract
The effect of small perturbations on steady nonlinear transonic small disturbance flowfields, in the context of two-dimensional flows governed by the general-frequency transonic small disturbance equation with nonreflecting far-field boundary conditions, is investigated. This paper presents a time-linearised time-domain solution method that includes effects due to the shock-generated entropy and vorticity and shock wave motions. The solution procedure correctly accounts for the small-amplitude shock wave motion due to small unsteady changes in the aerofoil boundary conditions, and correctly models a flowfield with embedded strong shock waves. Steady and first harmonic pressure distributions for the NACA 0003 aerofoil with a harmonically oscillating flap, and NACA 0012 aerofoil undergoing a sinusoidal pitching oscillation, are predicted and compared with the Euler results.

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Volume 107, Number 1078   December 2003

The birth of flight control - An engineering analysis of the Wright brothers 1902 glider

Authors
G D Padfield & B Lawrence

Abstract
In the autumn of 1902 the Wright brothers spent just over eight weeks at their test site in the Kill Devil Hills near Kitty Hawk, North Carolina, testing their third Glider design. During the trial period they implemented an inter-linked roll-yaw control system. Together with the forward canard surface, this gave them control over vertical and horizontal components of the flight path. They were also able to hone and perfect their piloting skills. In just two days in the final week, they made about 250 glides. The success of the trials instilled the confidence in the Wright brothers to proceed rapidly to the construction of a powered aircraft. Within a month of returning to Dayton, they were writing to engine manufacturers with their specification – an engine that would develop eight to nine brake horse power, weigh no more than 180lb and be free from vibration; they would not find a suitable powerplant and had to design and build their own.

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Volume 107, Number 1078   December 2003

Numerical investigation of staged transverse sonic injection in Mach 2 stream in confined environment

Authors
D Chakraborty, A P Roychowdhury, V Ashok & P Kumar

Abstract
Transverse sonic injection, usually in a staged manner, in a confined environment is a necessity in the design of an efficient combustion chamber. The design requires an analysis of the mixing of the injectant with incoming stream as efficient combustion depends upon good mixing. This kind of analysis needs numerical model/simulation to assess the mixing of the two streams. To determine the suitability of an existing software package for such a study, staged transverse sonic injection into a Mach 2 stream in a confined environment is taken as a test case. The experimental conditions of McDaniel et al are reproduced for this simulation. In this experiment, staged transverse injection of sonic jet behind the backward facing step in Mach 2 stream was carried out and profiles of various flow parameters were measured. The numerical simulation solves the 3D Navier- Stokes equations with a k – å turbulence model using the PARallel Aerodynamic Simulator PARAS3D.

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Volume 107, Number 1078   December 2003

Progress in the development of a versatile pilot model for the evaluation of rotorcraft performance, control strategy and pilot workload

Authors
R Bradley & G Brindley

Abstract
The evaluation of rotorcraft performance and handling qualities in piloted flight using a desk-top simulation is a desirable facility. The development of the SYCOS pilot model has brought this capability closer by simulating piloted flight along prescribed trajectories such as the Mission Task Elements of ADS-33. This development has overcome some of the limitations of the precise control of inverse simulation, by adopting a structure which includes a corrective component that adjusts the control strategy to counteract departures from the desired flight path. The development and implementation of SYCOS for a range of rotorcraft types and applications is shown to be well defined and straightforward. The capability and reliability of SYCOS is demonstrated through a number of recent applications in performance, control strategy and pilot workload studies. Some of the applications benefit from enhancements to the basic structure and these are described in context.

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Volume 107, Number 1078   December 2003

The effects of apex flap on the leading-edge vortex breakdown of a cropped double delta wing

Authors
J J Wang, J Y Liu & Q S Li

Abstract
The dye-injection flow visualisation technique was used to investigate the effect of the apex flap on the leading-edge vortex breakdown over a cropped 76°/40° double delta wing. The angle-of-attack of the experimental model varied from 20° to 40°, and the length of the apex flap was 25%c and 50%c respectively. By changing the angle of the apex flap, we found that the apex flap is an efficient method to control the leading-edge vortex breakdown, and that there exists an angle of the apex flap at which the value of the leadingedge vortex breakdown delay reaches maximum. Moreover, it is found that, for á < 28°, the small apex flap is a better choice for delaying the vortex breakdown; for á > 28°, the large apex flap is superior to the small one.

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Volume 107, Number 1078   December 2003

An investigation into the longitudinal dynamics and control of a flapping wing micro air vehicle at hovering flight

Authors
K Loh, M Cook & P Thomasson

Abstract
This paper describes the research into the flight dynamics modelling and flight control of a flapping wing micro aerial vehicle (MAV). The equations of motion based on a multi-body representation of the vehicle and the flapping wings were derived and form the basis for the simulation program, which was developed using MATLAB and SIMULINK. The aerodynamic forces were obtained through experimental methods and form the basis for the aerodynamic model. The hovering and low speed flight of the MAV was investigated using a SIMULINK simulation model. Various flight control concepts, inspired by observation of insect and bird flight, were investigated in some detail. The concepts include the control of flap frequency, flap and pitch phasing (wing beat kinematics) and shift in centre of gravity position. The paper concludes with a comparison of the control concepts and their feasibility for a practical vehicle application.

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Volume 108, Number 1079   January 2004

Validation of a rotorcraft mathematical model in autorotation by use of gyroplane flight tests

Authors
V M Spathopoulos

Abstract
Aircraft handling qualities in autorotation are critical in determining the level of safety of rotorcraft. For helicopters suffering from an engine failure, transcending from powered to autorotative flight occurs rapidly and requires immediate and accurate pilot reaction. Although it is important for the handling qualities in this flight state to be predicted correctly, obvious difficulties will exist in using flight tests as a means of validation when autorotation constitutes an abnormal mode of operation. In the research work presented in this paper an alternative approach is applied, of configuring a generic rotorcraft model as a gyroplane, a type of vehicle for which its main rotor is constantly in autorotation. Flight tests are used for the validation purposes both for steady state and dynamic response cases. Results are produced to complement those already existing for a dissimilar gyroplane type thus increasing the level of confidence obtained.

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Volume 108, Number 1079   January 2004

A turbulence model study of separated 3Djet afterbody flow

Authors
R G M Hasan, J J McQuirk, D D Apsley & M A Leschziner

Abstract
Three-dimensional RANS calculations and comparisons with experimental data are presented for subsonic and transonic flow past a nonaxisymmetric (rectangular) nozzle/afterbody typical of those found in fast-jet aircraft. The full details of the geometry have been modelled, and the flow domain includes the internal nozzle flow and the jet exhaust plume. The calculations relate to two free-stream Mach numbers of 0⋅6 and 0⋅94 and have been performed during the course of a collaborative research programme involving a number of UK universities and industrial organisations. The close interaction between partners contributed greatly to the elimination of computational inconsistencies and to rational decisions on common grids and boundary conditions, based on a range of preliminary computations.

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Volume 108, Number 1079   January 2004

Modelling a helicopter rotors response to wake encounters

Authors
G R Whitehouse & R E Brown

Abstract
In recent years, various strategies for the concurrent operation of fixed- and rotary-wing aircraft have been proposed as a means of increasing airport capacity. Some of these strategies will increase the likelihood of encounters with the wakes of aircraft operating nearby. Several studies now exist where numerical simulations have been used to assess the impact of encounters with the wakes of large transport aircraft on the safety of helicopter operations under such conditions. This paper contrasts the predictions of several commonly-used numerical simulation techniques when each is used to model the dynamics of a helicopter rotor during the same idealised wake encounter.

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Volume 108, Number 1079   January 2004

Vortex interaction and breakdown over double-delta wings

Authors
S L Gai, M Roberts, A Barker, C Kleczaj & A J Riley

Abstract
Modern high-speed aircraft, especially military, are very often equipped with single or compound delta wings. When such aircraft operate at high angles-of-attack, the major portion of the lift is sustained by streamwise vortices generated at the leading edges of the wing. This vortex-dominated flow field can breakdown, leading not only to loss of lift but also to adverse interactions with other airframe components such as the fin or horizontal tail. The wind tunnel and water studies described herein attempt to clarify the fluid mechanics of interaction between the strake and wing vortices of a generic 76°/40° double-delta wing leading to vortex breakdown. Some studies of passive control using fences at the apex and kink region are also described. Various diagnostic methods-laser sheet flow visualisation, fluorescent dyes, and pressure sensitive paints have been used.

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Volume 108, Number 1079   January 2004

Control laws for an active tunable vibration absorber designed for rotor blade damping augmentation

Authors
F Nitzche, D G Zimcik, V K Wickramasinghe and C Young

Abstract
Most Individual Blade Control (IBC) approaches have attempted to suppress the rotor vibration by actively altering the varying aerodynamic loads on the blade using techniques such as trailing-edge servoflaps or imbedded piezoelectric fibres to twist the blade. Unfortunately, successful implementation of these approaches has been hindered by electromechanical limitations of piezoelectric actuators. The Smart Spring is an unique approach that is designed to suppress the rotor vibration by actively altering the structural stiffness of the blade out of phase with the time varying aerodynamic forces. The Smart Spring system is able to adaptively alter the stiffness properties of the blade while requiring only small deformations of the actuator, which overcomes the major problems inherent in the former approaches.

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Volume 108, Number 1080   February 2004

Linear and non-linear turbulence model predictions of vortical flows in lobed mixers

Authors
H Salmon, D Jiang, G J Page & J J McQuirk

Abstract
Lobed mixers are widely used in gas turbine engines to increase mixing between hot and cold streams and consequently reduce jet noise. CFD predictions are presented for a simplified experimental configuration of a planar, three lobe geometry. Results are shown for a standard linear ê-å turbulence model, the same model with a time scale limitation invoked and a non-linear quadratic model also employing a time scale limitation. Comparisons are presented between the three models for axial velocity, velocity vectors, shear stress and turbulence kinetic energy at a selected plane in the mixing region. The non-linear model was found to have little influence on the mean flow but some effect on the turbulence structure was observed. Comparison with measurements showed that all major features were reproduced but detail differences were evident. The use of a time scale limit reduced peak values of predicted turbulence quantities by 20-30%.

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Volume 108, Number 1080   February 2004

Spacecraft control with constrained fast reorientation and accurate pointing

Authors
G Mengali & A A Quarta

Abstract
In this paper we study large angle rotational manoeuvres of spacecraft. The problem of attitude control is formulated and solved through potential functions, thus simplifying frequent reorientation manoeuvres. A combination of gas jet and FEEP thrusters is employed in order to obtain short settling times while meeting stringent pointing requirements. In this way, spacecraft reorientation is achieved in two integrated steps by means of a discrete/continuous control law. Autonomous avoidance of undesired space orientations is obtained and constraints due to the solar array pointing requirements are satisfied. A case study is discussed where the methodology is applied to a large space telescope.

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Volume 108, Number 1080   February 2004

Active control of swept shock wave turbulent boundary layer interactions

Authors
J S Couldrick, S L Gai, J F Milthorpe & K Shankar

Abstract
This paper looks at active control of the swept shock wave/turbulent boundary-layer interaction using smart flap actuators. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the bleed/suction rate through a plenum chamber. The cavity provides communication of signals across the shock, allowing rapid thickening of the boundary-layer approaching the shock, which splits into a series of weaker shocks forming a lambda shock foot, reducing wave drag. Active control allows optimum control of the interaction, as it would be capable of positioning the control region around the original shock position and control the rate of mass transfer. The actuators are modelled using classical composite material mechanics theory, namely analysis of a laminate with a uniform cross section. Furthermore a finite element modelling program (ANSYS 5.7) was used to produce improved results.

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Volume 108, Number 1080   February 2004

Experimental investigation on wall pressure distribution in flaps separating regions

Authors
P F Zhang, J J Wang & Y C Li

Abstract
The effects on the wall pressure of the plate caused by the introduction of a gap near the ground and the flaps were investigated experimentally. The mean pressure on the plate surface was found to decrease with the size changing of the gap near the ground when the gap size (g) is larger than the flap height (h), but the one in the recirculation region increase with the size of the gap when the gap size is about 0 ¡Ü g ¡Ü 2h. Three kinds of flow structure appear with increasing the gap sizes, and the transit point is at g/h = 0⋅2, 0⋅8 respectively. For the zigzag flap (d/h = 0⋅19, d is the height of the zigzag), the variation of wall pressure with g/h is similar to the flat flap in general. The zigzag affects the mean wall pressure in the region of 0 ¡Ü x/h ¡Ü 20 (the recirculation zone) and can decrease the fluctuating pressure in the region of x/h > 20 downstream.

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Volume 108, Number 1080   February 2004

The effect of flap-end additions on aircraft trailing vortices

Authors
W R Graham, T berteny & L David

Abstract
The influence of flap-end geometry modifications on the near-field wake behind a generic high-lift wing/flap configuration is investigated experimentally with a single-tube yawmeter. It is found that flap-end additions tend to split the concentrated area of streamwise vorticity shed by the flap into two less intense regions, associated with the tips of the flap and the addition. For shorter additions, these regions tend to roll up together, resulting in a slightly more diffuse flap vortex of almost unchanged circulation. For larger additions, the outer region is captured by the tip vortex, which correspondingly gains in circulation at the expense of the flap vortex. In all cases, the vorticity centroid of the rolled-up wake is shifted outboard, and the overall circulation slightly increased. However, the associated lift increase implies a decrease in overall circulation at a given lift coefficient.

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Volume 108, Number 1081   March 2004

Design of formation control laws for manoeuvred flight

Authors
G Campa, S Wan, M R Napolitano, B Seanor & M L Fravolini

Abstract
This paper presents identification, control synthesis and simulation results for an YF-22 aircraft model designed, built, and instrumented at West Virginia University. The ultimate goal of the project is the experimental demonstration of formation flight for a set of 3 of the above models. In the planned flight configuration, a pilot on the ground maintains controls of the leader aircraft while a wingman aircraft is required to maintain a pre-defined position and orientation with respect to the leader. The identification of both a linear model and a nonlinear model of the aircraft from flight data is discussed first. Then, the design of the control scheme is presented and discussed with an emphasis on the amount of information, relative to the leader aircraft, needed by the wingman to maintain formation. Using the developed nonlinear model, the control laws for a maneuvered flight of the formation are then simulated with Simulink® and displayed with the Virtual Reality Toolbox®.

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Volume 108, Number 1081   March 2004

Experimental and numerical investigation of confined unsteady supersonic flow over cavities

Authors
T K G Anavaradham, B U Chandra, V Babu, S R Chakravarthy & S Panneerselvam

Abstract
Experimental investigations were carried out to study the acoustic radiation from a rectangular wall mounted cavity in a confined supersonic flow. The free-stream Mach number was maintained at 1⋅5 and the cavity length-to-depth ratio was varied from 0⋅43 to 5⋅0. Acoustic measurements made on the top wall show jumps in the dominant frequency as the cavity behaviour changes from shallowto- square-to-deep cavity. Numerical simulations of this unsteady two-dimensional flow using the commercially available software FLUENT have also been carried out. Unsteady pressure data at the same location in the flow field as the pressure transducers in the experiments was collected. FFT analysis of the unsteady pressure data was performed to obtain the dominant acoustic frequencies. The values for these dominant frequencies predicted by the numerical calculations agree well with experimental data. The numerical study also predicts the frequency jump observed in experiments.

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Volume 108, Number 1081   March 2004

An experimental and numerical investigation of under-expanded turbulent jets

Authors
A J Saddington, N J Lawson & K Knowles

Abstract
The work described here concentrates on under-expanded, axisymmetric turbulent jets issuing into quiescent conditions. Underexpanded turbulent jets are applicable to most aircraft propulsion applications that use convergent nozzles. Experimental studies used laser doppler velocimetry (LDV) and pitot probe measurements along the jet centreline. These measurements were made for two nozzle pressure ratios (2·5 and 4·0) and at various streamwise positions up to 10 nozzle diameters downstream of the nozzle exit plane. A computational fluid dynamics (CFD) model was developed using the Fluent code and utilised the RNG ê−å two-equation turbulence model. A mesh resolution of approximately one hundredth of nozzle exit diameter was found to be sufficient to establish a mesh independent solution.

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Volume 108, Number 1081   March 2004

Oscillating behaviour of laminar separation bubble formed on an aerofoil near stall

Authors
K Rinoie & N Takemura

Abstract
Laminar separation bubbles formed on NACA 0012 aerofoil near the onset of a stall were investigated to clarify the behaviour of the laminar separation bubble. Measurements were done at a chord Reynolds number of 1·3 x 105. Mean velocity measurements indicate that the long bubble of about 35% chord length is formed at á = 11·5° after the short bubble burst occurred. However, the instantaneous flow visualisation picture indicates that the flow is strongly oscillating at this angle of attack. The phase averaging technique has been applied to analyse this oscillating behaviour. The results indicate that the flow is oscillating between a small separation-reattachment bubble formed near the leading-edge at about a 10% chord length and a large separated region extending over the aerofoil surface. It is suggested that this small separation-reattachment bubble has a similar flow structure to that of the short bubble formed at a lower angle of attack.

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Volume 108, Number 1082   April 2004

Load alleviation in tilt rotor aircraft through active control: modelling and control concepts

Authors
B Manimala, G D Padfield, D Walker, M Naddei, L Verde, U Ciniglio, P Rollet & F Sandri

Abstract
This paper presents the first results from research into active control of structural load alleviation (SLA) for tiltrotor aircraft carried out in the European ‘critical technology’ RHILP project. The importance of and the need for SLA in tiltrotors are discussed, drawing on previous US experience reported in the open literature. The paper addresses the modelling aspects in some detail; hence forming the foundation for both the FLIGHTLAB simulated XV-15 and EUROTILT configurations. The primary focus of attention is the suppression of in-plane rotor yoke loads for pitch manoeuvres in airplane mode; without suppression these loads would result in a very high level of fatigue damage. Multi-variable control law design methods are used to develop controller schemes and load suppression of 80-90% is demonstrated using rotor cyclic control, albeit at a 20-30% performance penalty.

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Volume 108, Number 1082   April 2004

Control of plume interference effects on axisymmetric afterbodies

Authors
Y-K lee, S Raghunathan, E Benard, H-D Kim & T Setoguchi

Abstract
Plume interference effects on the axisymmetric flowfields around powered missiles are investigated using computational techniques. The study is mainly to understand the physics of the plume-induced shock and separation particularly at high plume to exit pressure ratios with and without shock-turbulent boundary layer control methods. Mass-averaged Navier-Stokes equations with the RNG k-å turbulence model are solved using a fully implicit finite volume scheme and time-marching algorithm. The shock position and extent of separation was found to be dependent on the freestream Mach number and plume pressure ratio. Rounding the tail or a groove on the surface near the tail moved the shockwave downstream of the tail fin which should enhance the control of the missile.

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Volume 108, Number 1082   April 2004

Analysis of anisotropic prismatic sections

Authors
G F J Hill & P M Weaver

Abstract
The dynamic behaviour of rotor blades is often modelled using onedimensional beam analysis with equivalent mass and stiffness properties to those of the full blade. Calculation of accurate elastic stiffness terms for these arbitrarily shaped sections with differing material properties is vital to this process. A method which produces these properties using standard finite element analysis codes is presented. The method is then compared with theoretical results for a simple rectangular section beam and case studies are performed on a composite laminate and box-section.

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Volume 108, Number 1082   April 2004

Robotic in-orbit servicers - the need for control moment gyroscopes for attitude control

Authors
A Ellery

Abstract
Robotic in-orbit servicing has yet to be realised due to a number of technical difficulties. One such difficulty is analysed here. The requirement for force control in robotic manipulation imposes significant design requirements on space robots by virtue of the lack of a mounting platform to react against external forces and torques. The spacecraft attitude control system must effectively serve the same role as the ground in terrestrial manipulators. The reaction torques imposed on the spacecraft due to the manipulators is high when force control is used in grappling targets in space, limiting the choice of attititude actuator to control moment gyroscopes.

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Volume 108, Number 1082   April 2004

Fuel sensitivity analyses for active drag reduction systems

Authors
T M Young

Abstract
Active drag reduction systems, such as hybrid laminar flow control (HLFC), have the potential for significant fuel savings; however, this is at the expense of an increase in aircraft weight and engine power off-take. A computer program – capable of accurately determining the trip fuel for a given mission profile – has been developed. The program was validated against manufacturer’s payload-range data, and then modified to emulate the installation of an active drag reduction system, by incorporating changes to the drag polars, specific fuel consumption (SFC) data and operating empty weight (OEW). Results of sensitivity studies are presented that enable the reduction in trip fuel to be determined for given changes in CD, SFC and OEW. The underlying assumption of linear independence of the three parameters is explored.

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Volume 108, Number 1083   May 2004

Airspace safety in New Zealand: A Causal analysis of controller caused airspace incidents between 1994 - 2002

Authors
A Maajumder & P Nalder

Abstract
The New Zealand Government takes airspace safety very seriously. The level of safety in New Zealand airspace is measured by the number of recorded airspace incidents. An airspace incident can be thought of as a failure in the chain of operations in the air traffic system when it is provided with an air traffic service (ATS). Some of these incidents result in a loss of separation between aircraft, varying from slight to a very serious loss with a significant risk of collision, known as a near collision. New Zealand’s Civil Aviation Authority (CAA) identifies the causal factors for all airspace incidents using the Reason model of human error, divided into three areas; active failures committed by individuals involved in the incident, local factors relating to the task and the ATS environment and organisational factors originating in the managerial and organisation spheres of the ATS provider.

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Volume 108, Number 1083   May 2004

Derivation of control activity metrics for the rule-based prediction of helicopterpilot workload

Authors
C A Macdonald & R Bradley

Abstract
Control activity is a recognised gauge of pilot workload and recent research has employed wavelet decomposition to classify discrete control actions into categories such as guidance and stabilisation. The aim of the present work is to extend the wavelet approach so that workload may be quantified through sets of rules based on appropriate control activity metrics. The rules are derived from data collected in piloted simulation trials of a variety of flying tasks involving a number of pilots and different helicopter configurations. Statistical tests are then applied which test the efficacy of the derived rules. The immediate aim of the research is to establish whether workload can be successfully predicted from control responses. The underlying goal however, is to be able to predict workload ratings from desktop simulations in order to provide indicative workload information at the design stage. The contribution of the current study to this objective is discussed.

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Volume 108, Number 1083   May 2004

Multigrid multiblock hovering rotor solutions

Authors
C B Allen

Abstract
The effect of multigrid acceleration implemented within an upwind- biased Euler method for hovering rotor flows is presented. Previous work has considered multigrid convergence for structured single block rotor solutions. However, for forward flight simulation a multiblock approach is essential and, hence, the flowsolver has been extended to include multigrid acceleration within a multiblock solver. The requirement to capture the vortical wake development over several turns means a long numerical integration time is required for hovering rotors, and the solution (wake) away from the blade is significant. Hence, the solution evolution and convergence is different to a fixed wing case where convergence depends primarily on propagating errors away from the surface as quickly as possible, and multigrid acceleration is shown here to be less effective for hovering rotor flows.

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Volume 108, Number 1083   May 2004

Notched strength estimations of graphite epoxy composite laminates containing central holes and cracks: A statistical approach

Authors
P K G Potti, B N Rao & V K Srivastava

Abstract
A statistical approach is followed for prediction of tolerences of notched strength of composite laminates using the recently proposed improved inherent flaw model (IFM). In order to examine the validity of this approach, the existing fracture data on graphite/epoxy composite laminates containing central holes and cracks were used. The notched strength estimations are found to be within the range of tested values.

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Volume 108, Number 1084   June 2004

Aerodynamic forces and moments on an ogive cylinder at incidence

Authors
S C Luo, Y T Ng & T T Lim

Abstract
In flows over an ogive cylinder placed at incidence, it is well documented that a side force acts on the cylinder. However, little is known about the relation between the side force (CFy) and other force and moment components. In this note, the variations of three force and three moment components, acting on the ogive cylinder, with roll angle are measured simultaneously. The model was placed at four different angles-of-attack, namely á = 30°, 45°, 50° and 60° and the results show that in addition to CFy, the variation of CFz, CMx, and CMz with the roll angle also exhibit the square wave like behaviour at á = 45° and 50°, and with the same cross over ö positions, while CFx and CMy remain relatively constant irrespective of the roll angle. The magnitudes of CFx and CMy were found to increase with angle of attack and were thought to be due to the increase in normal frontal area.

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Volume 108, Number 1084   June 2004

A novel method for the provision of flight experience and flight testing for undergraduate aeronautical engineers at the University of Strathclyde

Authors
M T Strickland & T J Scanlon

Abstract
The Department of Mechanical Engineering at the University of Strathclyde has developed a novel flight experience/test course for undergraduate Aeronautical Engineers. In common with similar courses at undergraduate level the course contains practical instruction in how an aircraft is flown, an analysis of its stall characteristics and an assessment of an aircraft’s performance and stability. However, uniquely, the Strathclyde course consists of dual instructional flights in two seat gliders. This paper contains a detailed description of the flight experience/test course developed at Strathclyde and its incorporation into the undergraduate curriculum. A critical analysis of its delivery is also presented.

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Volume 108, Number 1084   June 2004

Supersonic transport aircraft longitudinal flight control law design

Authors
A J Steer

Abstract
Modern civil transport aircraft utilise increasingly complex command and stability augmentation systems to restore stability, optimise aerodynamic performance and provide the pilot with the optimum handling qualities. Provided it has sufficient control power a second generation fly-by-wire supersonic transport aircraft should be capable of exhibiting similarly desirable low-speed handling qualities. However, successful flight control law design requires identification of the ideal command response type for a particular phase of flight, a set of valid handling quality design criteria and piloted simulation evaluation tasks and metrics. A non-linear mathematical model of the European supersonic transport aircraft has been synthesized on the final approach to land. Specific handling quality design criteria have been proposed to enable the non-linear dynamic inversion flight control laws to be designed, with piloted simulation used for validation.

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Volume 108, Number 1084   June 2004

On wake vortex response for all combinations of five classes of aircraft

Authors
L M B C Campos & J M G Marques

Abstract
The present paper concerns the response of a following airplane to a pair of wing tip vortices left by a leading aircraft, represented by the Hallock-Burnham model, including the effect of vorticity decay between the two aircraft. The effect of vorticity is evaluated in terms of the induced rolling moment and also the lift loss; these specify the roll acceleration and the downward acceleration, respectively. The corresponding two response equations can be put into the same dimensionless form, and integrated using exponential integrals. This specifies the roll rate and sink rate as a function of time; besides the latter, the bank angle and altitude loss, are also plotted, all also as a function of time, for all combinations of leading and following aircraft in five classes.

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Volume 108, Number 1085   July 2004

State-space inflow modelling for lifting rotors with mass injection

Authors
K Yu and D A Peters

Abstract
In the field of rotorcraft dynamics, it is significant that the induced inflow field is well understood and modeled. A large number of methodologies have been developed in the past years, among which the state-space model is recognised for its advantage in real-time simulation, preliminary design, and dynamic eigenvalue analysis. Recent studies have shown success in representing the induced flow field everywhere above the rotor plane even with mass source terms on the disk as long as they have zero net flux of mass injection when integrated over the disk. Nevertheless, non-zero net mass influx is expected in numerous situations, such as ground effect, tip drive rotors, etc; and the incapability of previous models limits the utilisation of the methodology in these cases.

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Volume 108, Number 1085   July 2004

Unsteady aerodynamic model of a cargo container for slung-load simulation

Authors
L S Cicolani, J G A da Silva, E P N Duque and M B Tischler

Abstract
The problem of simulation models capable of predicting the aerodynamic instability of helicopter slung-load cargo containers and bluff bodies is addressed. Instability for these loads is known to depend on unsteady frequency-dependent aerodynamics, but simulation models that include the unsteady aerodynamics do not currently exist. This paper presents a method for generating such models using computational fluid dynamics (CFD) to generate forced-oscillation aerodynamic data and frequency domain system identification techniques to generate a frequency response from the CFD data and to identify a transfer function fit to the frequency response. The method is independent of the responsible flow phenomenon and is expected to apply to bluff-bodies generally. Preliminary results are presented for the case of the 6- by 6- by 8-ft CONEX (container express) cargo container.

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Volume 108, Number 1085   July 2004

Dynamic modelling and stability of hingeless helicopter blades with a smart spring

Authors
F F Afagh, F Nitzche and N Morozova

Abstract
The aeroelastic stability of a uniform, untwisted hingeless ‘smart’ helicopter rotor blade in hover has been analysed. The concept of a ‘smart’ blade is achieved by implementing a piezoelectric stack at an appropriate location along a host blade such that upon actuation it enters the load path becoming an integral part of the host structure. Thus, the stiffness characteristics of the rotor are altered causing modal damping augmentation of the blade. The perturbation equations of motion for the ‘smart’ blade that describe the unsteady blade motion about the equilibrium operating condition are obtained using Galerkin’s method. These differential equations with periodic time coefficients are analysed for stability utilising the Floquet method. Six different regimes of actuation are investigated, and a parametric study is carried out by considering six different design cases.

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Volume 108, Number 1085   July 2004

Experimental and numerical aerodynamic analysis of a satellite launch vehicle eith strap-on boosters

Authors
A Naghib-Lahouti, M Mani and M Nazarinia

Abstract
Results of numerical simulation of inviscid compressible flow around a generic satellite launch vehicle (SLV) with strap-on boosters using a commercial computational fluid dynamics (CFD) code named Star-CD are experimentally evaluated. Governing equations of flow around the SLV with two and two strap-on boosters were solved in three dimensions using the SIMPLE algorithm in an unstructured tetrahedral mesh, to determine longitudinal aerodynamic coefficients and surface pressure distribution at Mach numbers from 0·6 to 2·0, and angles-of-attack from 0° to 16°. To evaluate the numerical results, 1:100th scale models of the SLV were tested in a trisonic wind tunnel in the same configurations and flow conditions as those analysed numerically. Comparison of results shows reasonable agreement between numerical and experimental values, however, drag coefficients had to be corrected to compensate the effects of base flow and the struts connecting the boosters to the core rocket.

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Volume 108, Number 1086   August 2004

A structure coupled CFD method for time-marching flutter analysis

Authors
N V Taylor, C B Allen, A Gaitonde and D P Jones

Abstract
Aeroelastic analysis is a critical area of the aircraft design process, as a good understanding of the dynamic behaviour of the wing structure is essential to safe operation of the vehicle. The inevitable inaccuracies present in the modelling of such phenomena impose mass penalties, as large safety margins are necessitated, which in turn lead to overly stiff designs. In an effort to reduce the uncertainty in analysis methods, fully coupled CFD and structural models are under widespread development. This paper describes the results produced by such a system for a series of test cases based on the AGARD445.6 and MDO wings. Results relating to the latter are of particular interest, as significant variations were found to be produced by the different methodologies used in previous studies, the precise cause of which could not be isolated.

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Volume 108, Number 1086   August 2004

Control of trailing edge separation by tangential blowing inside the bubble

Authors
P R Viswanath and K T Madhavan

Abstract
Experiments have been performed investigating the effectiveness of steady tangential blowing, with the blowing slot located downstream of separation (but inside the separation bubble) to control a trailingedge separated flow at low speeds. Trailing-edge separation was induced on a two-dimensional aerofoil-like body and the shear layer closure occurred in the near-wake. Measurements made consisted of model surface pressures and mean velocity, turbulent shear stress and kinetic energy profiles in the separated zone using a two-component LDV system. It is explicitly demonstrated that the novel concept of tangential blowing inside the bubble can be an effective means of control for trailing-edge separated flows as well. Blowing mass and momentum requirements for the suppression of wall and wake flow reversals have been estimated.

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Volume 108, Number 1086   August 2004

Flow visualisation experiments for turbine film cooling

Authors
C A Coat and G D Lock

Abstract
Flow visualisation experiments related to turbine film cooling have been conducted. These investigated the fluid mechanics of coolant ejection using a large-scale, flat-plate model at engine-representative Reynolds numbers in a low-speed tunnel with ambient-temperature mainstream flow. The coolant trajectories were captured using a fine nylon mesh covered with thermochromic liquid crystals, allowing measurement of gas temperature contours in planes perpendicular to the flow.

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Volume 108, Number 1086   August 2004

Aeroelastically adaptive propeller using blades root flexibility

Authors
Y Sandek and A Rosen

Abstract
Usually a fixed pitch propeller is designed to be optimal at cruise speeds. Thus the efficiency is quite low at takeoff or low speeds, as well as during other flight regimes. The present paper shows that by introducing a flexible element into the blade root, the propeller efficiency can be improved over a wide range of velocities. The flexible element reacts to root flap or torsion moments by changing the blade pitch at the root. The root flexibility and the pitch angles at the root at zero loads are chosen such that efficiency will increase during problematic regimes without decreasing the propeller thrust. In the case of straight blades the torsional moment at the root is too small to be used. In the case of swept blades this moment component is significantly increased and can contribute to the design of an optimal aeroelastically adaptive propeller.

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Volume 108, Number 1087   September 2004

Vortex breakdown location over 65deg delta wings empiricism and experiment

Authors
CE Jobe

Abstract
Thirty-eight data sets from static tests of various 65° delta wings in many water and wind tunnels are compared with four empirical vortex breakdown location prediction methods and the results of two Navier-Stokes computations to assess their range of validity in pitch. Vortex breakdown is the sudden expansion and subsequent chaotic evolution of the otherwise orderly, spiraling, leading-edge vortex flow over the upper surface. Large fluctuations occur in vortex breakdown location at static test conditions making accurate experimental determination difficult.

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Volume 108, Number 1087   September 2004

Design methodology and performance of an indraft wind tunnel

Authors
G Johl, M Passmore and P Render

Abstract
The design methodology and performance of Loughborough University’s new 1·9m × 1·3m, indraft wind tunnel is discussed in the following paper. To overcome severe spatial and financial constraints, a novel configuration was employed, with the inlet and exit placed adjacent to each other and opened to atmosphere. Using a fine filter mesh, honeycomb, two turbulence reduction screens and a contraction ratio of 7·3, flow uniformity in the working area of the jet at 40ms-1 is shown to be within 0·3% deviation from the mean velocity, with turbulence intensity in the region of 0·15%.

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Volume 108, Number 1087   September 2004

Investigation of active control of swept shock wave turbulent boundary-layer interactions - PSP results

Authors
J. S. Couldrick, S. L. Gai, J. F. Milthorpe and K. Shankar

Abstract
An investigation of active control of the swept shock wave/boundary-layer interaction using ‘smart’ flap actuators is presented. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the bleed/suction rate through a plenum chamber. The cavity provides communication of signals across the shock, allowing rapid thickening of the boundary layer approaching the shock. This splits the shock foot into a series of weaker shocks forming a lambda structure, thus reducing wave drag. Active control allows optimisation of the unimorph deflection, hence rate of mass transfer. In this paper, results of the interaction using pressure sensitive paint (PSP) are emphasised. It is shown that the use of PSP, in conjunction with discrete pressure data, enables the main features of the interaction to be observed when the actuators are subject to different deflections.

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Volume 108, Number 1087   September 2004

A question of survival – military aircraft vs the electromagnetic environment

Authors
M Pywell

Abstract
Military aircraft, by definition, need to survive the onslaught of opposing forces to successfully complete their mission. From an aircraft perspective, the electromagnetic (EM) environment can be an enabler, via the use of navigation aids, radar, radio communications etc. – in fact mission success depends on its successful use. However, this environment is also potentially a disabler, as threat weapon systems and the environment itself can harm or destroy the aircraft. This paper discusses risks and hazards thus posed to aircraft survivability, partitioned into two classes – ‘direct’ and ‘indirect’ EM threats. ‘Direct’ threats are those that occur as a result of direct coupling of EM energy to the airframe and systems within, e.g. lightning strike and directed energy weapons. ‘Indirect’ threats are those that utilise EM sensors to detect, track and target the aircraft, e.g. radar-guided surface-to-air missiles.

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Volume 108, Number 1088   October 2004

Vortex flows on UAVs: Issues and challenges

Authors
I. Gursul

Abstract
Separated and vortical flows are dominant over various unmanned air vehicles (UAVs). In this article, issues and challenges of vortical flows for future UAVs are reviewed. These include shear layer instabilities, vortex breakdown and wing stall, vortex interactions, nonslender vortices, multiple vortices, and manoeuvring wing vortices. There are also issues relating to vortical flows in certain flow/structure interactions, as well as in aerodynamics/propulsion interactions. Separated and vortical flows are even more dominant at low Reynolds number flows. The main features of vortical flows, unsteady aerodynamics, and propulsion related vortical flow isssues relevant to mini- and micro air vehicles, are discussed.

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Volume 108, Number 1088   October 2004

Air-to-ground targeting - UAVs, data links and interoperability (project Extendor)

Authors
K L Edwards

Abstract

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Volume 108, Number 1088   October 2004

Wind tunnel interference effects on a 70deg delta wing

Authors
M. R. Allan, K. J. Badcock, G. N. Barakos and B. E. Richards

Abstract

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Volume 108, Number 1088   October 2004

Optimising expansion deflection nozzles for vacuum thrust

Authors
N V Taylor and C M Hempsell

Abstract

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Volume 108, Number 1088   October 2004

Induced drag reduction of wing-wings and wings-ground configuration

Authors
L Marino

Abstract

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Volume 108, Number 1088   October 2004

An investigation of theflight dynamic characteristics of gyroplanes by use of flight tests

Authors
V M Spathopoulos

Abstract

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Volume 108, Number 1089   November 2004

The Fairey Rotodyne - technology before its time?

Authors
D Gibbings

Abstract
THE LEGACY OF JUAN DE LA CIERVA It cannot have escaped notice, that in two months time we will celebrate the centenary of the first flight of a powered aircraft carrying a man. We rightfully acclaim ‘The miracle at Kitty Hawk’ for all that it has meant to our chosen profession, albeit outside our remit as a rotorcraft section. There is however a significant 80th anniversary, which we can add to this centenary year. On 9 January 1923, a Cierva C-4 autogyro piloted by Lt Alejandro Gomez Spencer made an officially observed circular flight of over 4km (2⋅5 miles) in Madrid. This important event brought the name of Juan de la Cierva to the fore on the International scene, and was subsequently to prove to be the key to the modern helicopter, an interesting lesson in technology in that, Cierva never set out to invent the helicopter, and never produced one himself.

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Volume 108, Number 1089   November 2004

Effect of counter-rotating vortices on the development of aircraft wakes

Authors
A Panaras and S G Voutsinas

Abstract
A two-dimensional vortex particle model is used for studying the development of the vortex wake generated by the wing of an aircraft in the Trefftz plane. Two-dimensional, finite-area vortex structures simulate the initial vorticity distribution at a near-field cross-section of the wing, as provided by either measurements or simulations. The code is used for studying the effect of weak or strong counterrotating vortices on the development of an aircraft wake. Application in a three-vortex configuration, consisting of the tip and flap vortices, plus a weak negative vorticity sheet lying between them, supports the hypothesis of Graham(25) that the merging of the tip and flap vortices is prevented, because in such an arrangement the counter-rotating vorticity sheet is wrapped around the primary vortices.

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Volume 108, Number 1089   November 2004

Effects of hydrogen-air non-equilibrium chemistry on the performance of a model scramjet thrust nozzle

Authors
R. J. Stalker, N. K. Truong, R. G. Morgan and A. Paull

Abstract
Two aspects of hydrogen-air non-equilibrium chemistry related to scramjets are nozzle freezing and a process called ‘kinetic afterburning’ which involves continuation of combustion after expansion in the nozzle. These effects were investigated numerically and experimentally with a model scramjet combustion chamber and thrust nozzle combination. The overall model length was 0⋅5m, while precombustion Mach numbers of 3⋅1±0⋅3 and precombustion temperatures ranging from 740K to 1,400K were involved. Nozzle freezing was investigated at precombustion pressures of 190kPa and higher, and it was found that the nozzle thrusts were within 6% of values obtained from finite rate numerical calculations, which were within 7% of equilibrium calculations. When precombustion pressures of 70kPa or less were used, kinetic afterburning was found to be partly responsible for thrust production, in both the numerical calculations and the experiments.

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Volume 108, Number 1089   November 2004

Impact on composite structures

Authors
G Davis and R Olsson

Abstract
The problem of impact damage in laminated composite structures, and the consequent reduction in residual strength, has been a topic of continual research for over two decades. The number of journal papers on the subject now runs into four figures and most have been conscientiously reviewed by Abrate(1991, 1994, 1998). This review is not intended to be in the academic tradition, with emphasis on acknowledging the authorship of all the various research initiatives. Instead we present our opinions so that the reader can appreciate our current understanding of the problem, our capability of predicting by analysis, and the scope of the design tools for avoiding structural damage, or at least designing damage tolerant aerospace structures. There are two types of impact, namely that when a foreign body strikes a structure, or in contrast that when a complete aircraft or helicopter suffers a crash landing of some sort. This latter case is usually discussed as ‘crashworthiness’ and has become a routine feature of automobile design where the energy-absorbing properties of ductile metals are exploited to the full. The objective here is to design a structure which can deform and absorb energy but leave the passenger compartment more or less intact. The first case of foreign body impact may span several orders of magnitude in impact velocity, with very different structural consequences. Dropped tools during manufacture or in service are relatively low velocity events in the range 4-8ms–1 with energies up to 50J. Impact due to runway debris at velocities up to 70ms–1 can be classified as intermediate velocity with again energies of about 50J. These low velocity impacts can be the most serious in nature for carbon/epoxy composites which have no elasto-plastic energy-absorbing mechanism, with consequently no clear visual evidence of permanent indentation. It is quite possible for a composite structure to suffer fibre damage and massive delamination between plies, but to recover after the impact with very little evidence of the event. Barely visible impact damage (BVID) is a hidden menace and the residual strength in compression may be only 30% of the undamaged value. Ballistic impact due to ordnance or missile fragments can be classified as ‘high velocity’ in the range 300 to 2,500ms–1. The projectiles may have a mass of only a few grams but their kinetic energy is now 10 to 20kJ. At these speeds the impact event will be so short that the structure may have no time to respond in global flexural or shear modes, and the main issue will be whether complete penetration occurs. Body armour, using various composite materials for example, can be designed to resist penetration. Finally the term ‘hyper-velocity’ has come to be applied to satellites and spacecraft which may be struck by micrometeorites at velocities of order 30-70kms–1! Here the impact duration is measured in nanoseconds, conventional heat transport is impossible and both the meteorite (silicon) and impacted structure will vaporise.(Andersen 2001, 2003) Indeed the aim of protective shields is to encourage this so that only a gaseous cloud hits the payload. For all forms of impact the structural designer must evaluate the threat and ensure that the structure can cope. This means that some analysis of the event must be undertaken. In this review we cover experimental studies to establish the nature of the impact damage for various structural types. ‘Theoretical’ analysis follows where we use the term for simple, often closed form, solutions where possible. This enables the designer more easily to understand the effects of the main variables such as the mass of the impactor, the mass and stiffness of the impacted structure and its geometry. Numerical simulation is next described with as many variables as possible in this limited review. Commercial computational codes for simulating impact, and the loading of the damaged structure, have become more user-friendly and less costly to use. A computational model frees the user from the need to approximate the global and local geometry, the material’s constitutive laws, and allows the user to simulate a strength test of the damaged structure after the impact event. Finally a brief mention is made of impact-resistant and crashworthy composite structures to show that ductile materials can actually be out-performed.

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Volume 108, Number 1090   December 2004

Enhancement of thrust reverser cascade performance using aerodynamic structural integration

Authors
J. Butterfield, H. Yao, M. Price, C. Armstrong, S. Raghunathan, E. Benard, R. Cooper and D. Monaghan

Abstract
This paper focuses on the design of a cascade within a cold stream thrust reverser during the early, conceptual stage of the product development process. A reliable procedure is developed for the exchange of geometric and load data between a two dimensional aerodynamic model and a three dimensional structural model. Aerodynamic and structural simulations are carried out using realistic operating conditions, for three different design configurations with a view to minimising weight for equivalent or improved aerodynamic and structural performance. For normal operational conditions the simulations show that total reverse thrust is unaffected when the performance of the deformed vanes is compared to the un-deformed case. This shows that for the conditions tested, the minimal deformation of the cascade vanes has no significant affect on aerodynamic efficiency and that there is scope for reducing the weight of the cascade.

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Volume 108, Number 1090   December 2004

Application of generic algorithms in aerodynamic optimisation design procedures

Authors
R. P. Clayton and R. F. Martinez-Botas

Abstract
Direct optimisation techniques using different methods are presented and compared for the solution of two common flows: a two dimensional diffuser and a drag minimisation problem of a fixed area body. The methods studied are a truncated Newton algorithm (gradient method), a simplex approach (direct search method) and a genetic algorithm (stochastic method). The diffuser problem has a known solution supported by experimental data, it has one design performance measure (the pressure coefficient) and two design variables. The fixed area body also has one performance measure (the drag coefficient), but this time there are four design variables; no experimental data is available, this computation is performed to assess the speed/progression of solution.

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Volume 108, Number 1090   December 2004

Achieving drag measurement accuracy from a high load capacity internal balance design

Authors
R Porter

Abstract
As one aspect of a balance research and development programme, engineers at the Aircraft Research Association (ARA) have addressed the unique problems associated with the design of an internal single piece balance suitable for small military type aircraft models that experience very high loads during a wind tunnel test. The paper details the nature of the problems and the stages undertaken in the design, manufacture and commissioning of an initial prototype balance followed by a re-designed version to meet the stringent requirements. Data from recent tests indicate the quality of the measurements and the suitability of the balance for the testing of fighter type aircraft.

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Volume 108, Number 1090   December 2004

Design criteria for conceptual sizing of primary flight controls

Authors
A J Steer

Abstract
The European Supersonic Commercial Transport’s control surface configuration is based largely on Concorde’s and has been scaled to provide comparable un-augmented stability and manoeuvre performance. Hence, optimising the surface size could provide significant performance benefits in terms of reduced drag, noise, structural and actuator power requirements. Adequate control power will be required to meet current civil aviation regulations whose primary aim is to ensure the aircraft can be flown safely during both normal and emergency operation. Additional design criteria, combined with the optimum longitudinal control laws, are required to ensure desirable handling qualities with minimum pilot workload.

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Volume 108, Number 1090   December 2004

Vortex flows on UAVs: Issues and challenges

Authors
I. Gursul

Abstract
Separated and vortical flows are dominant over various unmanned air vehicles (UAVs). In this article, issues and challenges of vortical flows for future UAVs are reviewed. These include shear layer instabilities, vortex breakdown and wing stall, vortex interactions, nonslender vortices, multiple vortices, and manoeuvring wing vortices. There are also issues relating to vortical flows in certain flow/structure interactions, as well as in aerodynamics/propulsion interactions. Separated and vortical flows are even more dominant at low Reynolds number flows. The main features of vortical flows, unsteady aerodynamics, and propulsion related vortical flow isssues relevant to mini- and micro air vehicles, are discussed.

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Volume 109, Number 1091   January 2005

Intergrated design of flight simulator motion cueing systems

Authors
Rudd Hosman Sunjoo Advani and Nils Haeck

Abstract
An advanced design process applicable to the specification of flight simulator cueing systems is presented in this paper. This process is based on the analysis of the pilot-vehicle control loop by using a pilot model incorporating both visual and vestibular feedback, and the aircraft dynamics. After substituting the model for the simulated aircraft, the analysis tools are used to adjust the washout filter parameters with the goal of restoring pilot control behaviour. This process allows the specification of the motion cueing algorithm. Then, based on flight files representative of the operational flight envelope, the required motion system space is determined. The motion-base geometry is established based on practical limitations, as well as criteria for the stability of the platform with respect to singular conditions. With this process the characteristics of the aircraft, the tasks to be simulated, and the missions themselves are taken into account in defining the simulator motion cueing system.

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Volume 109, Number 1091   January 2005

Flight control system damage simulation using freely flying models

Authors
S Sadovnychiy, A Ryzhenko and A Bentin

Abstract
This article deals with a damage simulation of flight control systems during a flight. As a subject of flight tests the model of a classic aerodynamic aircraft scheme is considered. This aircraft has highly swept wings a moderate wing elongation and all-moving horizontal tail surfaces. The diagrams of flight parameters from flight tests of the freely flying models with loss of a control surface in flight are given. The investigation results for the failures leading to a sharp drop in the stiffness of the control units in the pitch channel are given. The damage investigation in horizontal flight and in complex manoeuvres is given.

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Volume 109, Number 1091   January 2005

The vortex merger factor in aircraft wake turbulence

Authors
M. Mokry

Abstract
Vortex merger is studied within the context of two-dimensional discrete vortex sheets and demonstrated on two equally oriented circular vortices and aircraft tip and flap vortices. It is confirmed that, depending on the wing load distribution, the latter may or may not coalesce into a single counter-rotating pair. The interaction of a vortex with an equally oriented shear layer, governed by the same physical principle, suggests a possible intensification of an aircraft vortex in cross-wind shear.

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Volume 109, Number 1091   January 2005

Investigation into Clustering of Synthetic Jet Actuators

Authors
S. C. Liddle and N. J. Wood

Abstract
An investigation into the behaviour of clustered synthetic jet Actuators for flow-control applications is described. Experiments have been undertaken with two small-scale synthetic jet actuators in a zero-pressure gradient boundary-layer, in order to investigate the effect of configuration yaw angle and relative input signal phase. Oil-flow visualisation and hotwire anemometry techniques were used, demonstrating that changes in the downstream flow structure could be observed. Compared to a streamwise configuration, in which a symmetrical counter-rotating vortex pair was produced by the synthetic jet-boundary-layer interaction, a broader asymmetric interaction was produced in a 15° yaw configuration. Streamwise velocity contour plots, illustrating the development of the interaction downstream, over four phase angles, were presented. Significant differences in the PSD analyses of downstream streamwise velocity time histories were found, suggesting that input signal phase could influence the stability and hence effectiveness of flow structures used in flow-control applications.

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Volume 109, Number 1092   February 2005

Evaluation of CFD methods for transport aircraft high lift systems

Authors
R Rudnik, P Eilasson and J Perraud

Abstract
Major results and findings of the numerical work package of the European high lift programme EUROLIFT are outlined. The main objective of these studies is to validate and test numerical methods for the prediction of high lift flows for transport aircraft configurations. The activities comprise the assessment of current CFD methods for 3D flows, evaluation of means for code improvement, and transition prediction. All aspects are especially devoted to high lift flow problems. A general capability to predict maximum lift on a simplified wing/fuselage high lift configuration is demonstrated by a variety of different numerical approaches. In general, major shortcomings are the reliability and the accurate simulation of large separation areas and the turn-around time to compute 3D lift polars. Advanced turbulence modelling and numerical solver features, such as the preconditioning technique, show a potential to overcome these deficiencies. Promising results with respect to transition prediction were obtained on a swept high lift wing using a database method. The results obtained in the numerical activities represent major ingredients on the way to a consistent numerical approach for the simulation of transport aircraft high lift configurations including all maximum lift determining effects.

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Volume 109, Number 1092   February 2005

Experimental investigation of the effect of nozzle shape & test section perforation & stationary characteristics of flow field in the large transonic TsAGI T-128 wind tunnel

Authors
V.I. Biryukov, S.A. Glazkov, A.R. Gorbushin, A.I. Ivanov, A.V. Semenov

Abstract
The results are presented for a cycle of experimental investigations of flow field characteristics (static pressure distribution, static pressure fluctuations, upwash, boundary layer parameters) in the perforated test section of the transonic TsAGI T-128 wind tunnel. The investigations concern the effect of nozzle shape, wall open-area ratio, Mach and Reynolds numbers on the above-outlined flow characteristics. During the tests, the main wind tunnel drive power is measured. Optimal parameters of the nozzle shape and test section perforation are obtained to minimize acoustic perturbations in the test section and their non-uniformity in frequency, static pressure field non-uniformity, nozzle and test section drag and, accordingly, required main wind tunnel drive power.

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Volume 109, Number 1092   February 2005

2D Numerical study of circular synthetic jets in quiescent flow

Authors
H Tang S Zhong

Abstract
2D numerical simulations of flows generated by a synthetic jet actuator with a circular orifice were conducted at two different diaphragm displacement settings, one representing a typical laminar case and the other a fully turbulent case. The flow in the cavity was included in the computation in order to provide more accurate predictions. A velocity boundary condition was applied at the neutral position of the diaphragm to account for its temporal deformation. Comparisons were made between the computational results and existing PIV and hot-wire data in terms of the time sequence of the velocity vector field, velocity variations in space and with time. It is found that computational results for the laminar case agree well with the experimental data. Four turbulent models were tested for the fully turbulent case. It was found that the predictions using the RNG k-e and Standard k-e models were reasonably close to the experimental data. This initial study has produced some encouraging evidence for the capacity of FLUENT in simulating the key features of synthetic jets.

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Volume 109, Number 1092   February 2005

Industry applications of advanced flow diagnostics-expereience in the BAE systems ground effects rig

Authors
P. Curtis

Abstract
This paper reviews some of the work performed on the ground effects rig at BAE Systems in Warton, the now unique facility for modelling dynamic vertical landings and measuring hot gas ingestion. The paper discusses the flow diagnostic tools which have been used in recent times, up to the complexity of 3D PIV, and uses examples from the F-35 JSF programme to illustrate these. The paper hopefully demonstrates the difficulties of using these tools, as well as the benefits they can bring to a development programme. The ground effects rig is a facility designed to measure temperature rise in aircraft intakes during vertical manoeuvres close to the ground. It is a complex facility that comes as close as possible to accurately modelling the flowfields around an aircraft moving both vertically and horizontally near the ground, with the ability to model dynamic pitch and roll at the same time. Standard instrumentation for the models consists of rapid response thermocouples mounted in a rake at the engine face. 45 thermocouples of 0·05mm diameter with a time constant of about 10ms are used. Although, with its standard instrumentation, the rig can measure how much hot gas gets to the engine face, it doesn’t show how it got there, or where it came from, which is the knowledge required to improve the design. Hence there is a need for flow diagnostics.

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Volume 109, Number 1092   February 2005

Life before & after implementation of an acoustic noise reduction enclosure

Authors
B. Timmins

Abstract
This paper looks back on the designs and ambitions of ARA in resolving a long term acoustic noise problem which threatened ARA with closure. This paper today briefly looks back to the original issues but deals more fully with the later phases of a two phase project implementation and construction. ARA is now a truly ‘silent site’, where closure was once threatened, ARA has achieved the implementation of a bespoke noise reduction enclosure where 24-hour running has proved to be a reality. This paper looks at the design and construction phases, the ‘before and after’ noise footprints and at some of the financial benefits ARA has achieved. The ARA transonic wind tunnel is sited on an industrial estate on the north west perimeter of Bedford. When it was first built it was on an original farm site with no appreciable residential houses in close proximity. Since the early 1950s there has been considerable residential development around the ARA site resulting in the local householders complaining about the wind tunnel acoustic noise. In early 1999 ARA was obliged to consider several options for noise reduction measures to reduce the noise to within UK government statutory requirements. This paper deals briefly with the original noise nuisance characteristics and footprint, the noise reduction design and method that ARA selected and shows the construction phases, the further noise treatment ARA had to do on other major ancillary equipment to make ARA a truly quiet industrial site. The paper shows how ARA has utilised the resulting benefits of these investments to increase productivity and reduce costs, and the influence it has had on ARA’s financial health.

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Volume 109, Number 1092   February 2005

Infra-red signature reduction study on a small-scale jet engine

Authors
J. Dix, A.J. Saddington, K. Knowles and M.A. Richardson

Abstract
This paper presents infra-red signature data for a small-scale, low pressure ratio turbojet engine typical of that used in unmanned air vehicle applications. The aim of the study was to test a number of different convergent nozzle designs concentrating on those with trailing edge modifications. The engine used in the tests has a single stage centrifugal compressor and radial inflow turbine and is designed to produce approximately 150N of thrust at 103,500rpm using liquid propane fuel. The test rig consisted of a calibrated thrust stand whilst the engine was controlled through an electronic engine control unit and laptop PC. The jet plume was visualised using an infra-red spectroradiometer which yielded qualitative data across the infra-red spectrum. Simultaneous measurements were also made of the engine thrust. A Pitot probe was used to take pressure readings across different sections of the exhaust flow. Analysis of the infra-red signature of the engine exhaust plume and any thrust penalty yielded a performance comparison for each of the nozzles tested. Correlation of engine thrust with engine rpm showed that, within the accuracy of the measurements, there was no significant thrust penalty associated with the notched nozzles. Infra-red imagery of the plain and 60° notched nozzles indicated that the latter reduced the length of the hottest part of the exhaust plume by approximately 33%. The spectroradiometer data shows a significant reduction in spectral radiance for the CO2 wavelength of approximately 4·3µm when the notched nozzles are used. The 60° notched nozzle appeared to perform best in reducing the spectral radiance at this wavelength. Centreline total pressure measurements in the exhaust plume correlated well with the infra-red imagery in that a potential core length reduction of up to 30% could be achieved using the 60° notched nozzle. Total pressure contours recorded 20mm (0·43D) downstream of the nozzle exit plane suggest that the notched nozzles are promoting increased mixing through radial spreading of the jet possibly associated with increased streamwise vorticity (although the latter could not be confirmed). There were also signs that the jet plumes being investigated were swirling.

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Volume 109, Number 1093   March 2005

Jet thrust vectoring using a miniature

Authors
G Raman, S Packiarajan, G Papadropulos, C Weissman and S Raghu

Abstract
This paper presents a new approach to vectoring jet thrust using a miniature fluidic actuator that provided spatially distributed mass addition. The fluidic actuators used had no moving parts and produced oscillatory flow with a square wave form at frequencies up to 1·6kHz. A subsonic jet with an exit diameter of 3·81cm was controlled using single and dual fluidic actuators, each with an equivalent circular diameter of 1·06mm. The fluidic nozzle was operated at pressures between 20·68 and 165·47kPa. The objectives of the present work included documentation of the actuation characteristics of fluidic devices, assessment of the effectiveness of fluidic devices for jet thrust vectoring, and evaluation of mass flow requirements for vectoring under various conditions. Measurements were made in the flow field using a pitot probe for the vectored and un-vectored cases. Some acoustic measurements were made using microphones in the near-field and for selected cases particle image velocimetry (PIV) measurements were made. Thrust vectoring was obtained in low speed jets by momentum effects with fluidic device mass flow rates of only 2 × 10–4kg/sec (0·6% of main jet mass flow per fluidic oscillator). Although a single fluidic device produced vectoring of the primary jet, the dual fluidic device configuration (with two fluidic devices on either side of the jet exit) produced mass flux enhancement of 28% with no vectoring. Our results indicate that fluidic actuators have the potential for use in thrust vectoring, flow mixing and industrial flow deflection applications.

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Volume 109, Number 1093   March 2005

Neuro-fuzzy approach for performance optimisation of variable nozzle turbofan engine

Authors
T R Nada A A Hashem

Abstract
An algorithm employing adaptive neuro-fuzzy online identification and sequential quadratic programming optimisation techniques is developed to enhance aircraft engine performance. This algorithm is implemented and tested using digital simulation for two spool, mixed exhaust, variable geometry turbofan engine. Parametric study is conducted to select the proper measurable parameter that can represent the actual thrust during online optimisation. Subtractive clustering technique is applied to generate the minimum number of fuzzy rules that can model the engine performance at various input parameters and flight conditions. The resulting neuro-fuzzy system is then optimised through training algorithm to accurately represent the engine. This system can address engine variations by relearning the network using online measurements from the actual engine. Generating the optimum schedules and comparing them with those obtained from the complete non-linear engine model verify the algorithm. Benefits from this algorithm include fuel consumption savings, reductions in turbine inlet temperature, and preventing limit exceeding.

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Volume 109, Number 1093   March 2005

Industry applications of advanced flow diagnostics-expereience in the BAE systems ground effects rig

Authors
P. Curtis

Abstract
This paper reviews some of the work performed on the ground effects rig at BAE Systems in Warton, the now unique facility for modelling dynamic vertical landings and measuring hot gas ingestion. The paper discusses the flow diagnostic tools which have been used in recent times, up to the complexity of 3D PIV, and uses examples from the F-35 JSF programme to illustrate these. The paper hopefully demonstrates the difficulties of using these tools, as well as the benefits they can bring to a development programme. The ground effects rig is a facility designed to measure temperature rise in aircraft intakes during vertical manoeuvres close to the ground. It is a complex facility that comes as close as possible to accurately modelling the flowfields around an aircraft moving both vertically and horizontally near the ground, with the ability to model dynamic pitch and roll at the same time. Standard instrumentation for the models consists of rapid response thermocouples mounted in a rake at the engine face. 45 thermocouples of 0·05mm diameter with a time constant of about 10ms are used. Although, with its standard instrumentation, the rig can measure how much hot gas gets to the engine face, it doesn’t show how it got there, or where it came from, which is the knowledge required to improve the design. Hence there is a need for flow diagnostics.

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Volume 109, Number 1093   March 2005

Comprehensive validation of an intermittency transport model for transitional low-pressure turbine flows

Authors
Y. B. Suzen and P. G. Huang

Abstract
A transport equation for the intermittency factor is employed to predict transitional flows under the effects of pressure gradients, freestream turbulence intensities, Reynolds number variations, flow separation and reattachment, and unsteady wake–blade interactions representing diverse operating conditions encountered in low-pressure turbines. The intermittent behaviour of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, mt, with the intermittency factor, g. Turbulent quantities are predicted by using Menter’s two-equation turbulence model (SST). The onset location of transition is obtained from correlations based on boundary-layer momentum thickness, accelaration parameter, and turbulence intensity. The intermittency factor is obtained from a transport model which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross stream direction. The intermittency transport model is tested and validated against several well documented low pressure turbine experiments ranging from flat plate cases to unsteady wake–blade interaction experiments. Overall, good agreement between the experimental data and computational results is obtained illustrating the predicting capabilities of the model and the current intermittency transport modelling approach for transitional flow simulations.

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Volume 109, Number 1094   April 2005

Collision avoidance within flight dynamics constraints for UAV applications

Authors
R. W. Penney

Abstract
Avoiding collisions with other aircraft is an absolutely fundamental capability for semi-autonomous UAVs. However, an aircraft avoiding moving obstacles requires an evasive tactic that is simultaneously very quick to compute, compatible with the platform’s flight dynamics, and deals with the subtle spatio-temporal features of the threat. We will give an overview of a novel prototype method of rapidly generating smooth flight-paths constrained to avoid moving obstacles, using an efficient trajectory-optimisation technique. Obstacles are described in terms of simple geometrical shapes, such as ellipsoids, whose centres and shapes can vary with time. The technique generates a spatio-temporal trajectory which offers a high likelihood of avoiding the volume in space-time excluded by the predicted motion of each of the known obstacles. Such a flight-path could then be passed to the aircraft’s flight-control systems to negotiate the threat posed by the obstacles. Results from a demonstration implementation of the collision-avoidance technique will be discussed, including non-trivial scenarios handled well within 100ms on a 300MHz processor.

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Volume 109, Number 1094   April 2005

Trade disputes in the commercial aircraft industry: A background note

Authors
K. Hayward

Abstract
The long-running debate between the US and the EU over government supports for large commercial aircraft has recently boiled over into a major dispute involving the World Trade Organisation (WTO). While the two sides have currently backed off from what could be a very damaging WTO outcome, there are still wide differences over the legitimacy of government supports (direct or indirect) for Airbus and Boeing airliners. This paper: · Describes the background to the current dispute. · Analyses the 1992 US–EU Agreement on Large Aircraft Subsidies. · Outlines the WTO Agreement on Subsidies and Countervailing Measures and the decision by the US to mount an action under the WTO complaints procedures against launch investment for Airbus and the EU’s counter claim against Boeing. · Considers the precedents set by the WTO rulings on the Brazilian–Canadian dispute over regional jet supports. · Summarises the US–EU complaints to the WTO. · Considers potential outcomes and the implications for the civil aerospace industry on both sides of the Atlantic. · Analyses the wider issues surrounding government intervention in the aerospace sector. The paper views the dispute as a reflection of fundamental differences, based primarily on divergent economic doctrines and values, between the US and the EU states. There could be especially damaging consequences for the EU should the WTO rule against the systems of repayable launch investment used by the Airbus governments. But both sides could lose heavily from the affair and there is a good case for maintaining some form of direct government intervention in civil aerospace technology acquisition, even near market research, in support of environmental sustainability objectives.

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Volume 109, Number 1094   April 2005

Experiments on the hypersonic turbulent shock-wave/boundary-layer interaction and the effects of surface roughness

Authors
S A Prince, M Vannahme and J L Stollery

Abstract
An experimental investigation was performed to study the effects of surface roughness on the Mach 8×2 hypersonic turbulent shock-wave–boundary-layer interaction characteristics of a deflected control flap configuration. In particular, the surface pressure and heat transfer distribution along a quasi-2D ramp compression corner model was measured for flap angles between 0° and 38°, along with a Schlieren flow visualisation study. It was found that surface roughness, of scale 10% of the hinge-line boundary layer thickness, significantly increased the extent of the interaction, while increasing the magnitude of the peak pressure and heat flux just aft of reattachment. The incipient separation angle for a fully turbulent, Mach 8×2 boundary layer with a hinge line Reynolds number of 1×44 × 106, was estimated at 28-29°, reducing to between 19-22° with the introduction of laminar sub-layer scale surface roughness.

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Volume 109, Number 1094   April 2005

Simulation and flight test of a temperature sensing stabilisation system

Authors
P. Herrmann and C. Bil

Abstract
Thermopile sensors detect electromagnetic radiation as a function of the object’s temperature. Because there is a temperature difference between the cold ground and the warm sky, these sensors could be used to detect the horizon and thus be used as a reference to stabilise a small aircraft, such as an unmanned aerial vehicle (UAV) in visual meteorological conditions (VMC). To verify this hypothesis, a system has been developed providing horizon detection using thermopile sensors to stabilise an R/C model aircraft. The aircraft has gone through a number of flight trials using remote control to enable and disable the stabilisation system. During the flight trials the aircraft was set at various attitudes when the system was enabled. The stabilisation system was able to assume wing level under various bank angles and weather conditions with minimum overshoot and oscillation. Although the system shows good performance during flight trials, most of the original design was done using trial and error. A design tool was needed to implement further improvements to the system and to efficiently implement it on other aircraft. This required a good understanding of the physical behaviour of the system and the interaction between the sensors, aircraft and the environment. A mathematical model of the overall system was developed using the MATLAB/Simulink environment to simulate the behaviour of the system under various conditions. The simulation results were then compared with actual flight experiments. This paper describes the modelling techniques used for the different system components and the results of the simulation compared to actual flight trials.

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Volume 109, Number 1095   May 2005

Limited life engines for UAVs

Authors
I. K. Clark

Abstract
The ever expanding range of applications for unmanned air vehicles covers a wide variety of powerplant requirements. While many vehicles are high value assets and demand similar powerplant attributes to a conventional manned aircraft, there is an emerging requirement for powerplants which are designed to a limited life philosophy. This covers a range of applications: at the simplest level there are vehicles where the mission definition dictates that attrition rates will be high, for

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Volume 109, Number 1096   June 2005

Kite performance testing by flying in a circle

Authors
J Stevenson K Alexander P Lynn

Abstract
With the advent of recreational sports like kite surfing and buggying, the performance of kites has become a market driven item. Producers increasingly require methods to measure and improve the performance of the kites they manufacture. The Mechanical Engineering Department at the University of Canterbury has been working with a local kite producer to develop testing procedures suitable for kite manufacturers. The primary performance measurement is the lift to drag ratio. An early test rig was mounted in the top of a car, but limitations inherent in the design meant that it lost precision as the lift to drag ratio approached that of more advanced kites. This led the investigators to look for alternatives, and resulted in the development of the circular flight method. This method allows the test apparatus to be tuned to the performance of each kite, significantly improving the precision of the results while reducing the time taken for each test. In their raw form, the L/D results are not quite the same as those of the more traditional methods. But they reflect the underlying aerodynamic characteristics, and when used comparatively they can be used in the kite development process. Alternatively, with suitable processing the circular flight results can be converted to the traditional forms.

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Volume 109, Number 1096   June 2005

Equipment failures in ATC: Finding an appropriate safety target

Authors
B. Subotic, W. Ochieng and A. Majumdar

Abstract
The aviation community is currently faced with various approaches for the determination of Target Levels of Safety (TLS). The targets are usually derived for a specific airspace region, for a specific type of operation or a specific phase of flight. Therefore, current practices support the determination of TLS for specific aviation components in isolation. This paper argues that the setting of a new safety target for aviation has to be driven by an integrated system approach. Relevant past research on TLS is reviewed and augmented with the results from operational reports from two countries. A possible safety target for the year 2020 is suggested and scoped down to estimate the safety budget for air traffic control (ATC) equipment. The paper concludes with a discussion of the results and recommends useful practices to achieve the proposed integrated safety approach.

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Volume 109, Number 1096   June 2005

Acoustic validation of a new code using particle wake aerodynamics and geometrically-exact beam structural dynamics

Authors
F Nitzsche and D G Opoku

Abstract
This paper describes the validation of a new code for prediction both aeroacoustic and aeroelastic behaviour of hingeless rotors. The structural component is based on a non-linear beam element model considering small strains and finite rotations, which uses a mixed variational intrinsic formulation. The aerodynamic component is built on a low-order panel method incorporating a vortex particle free-wake model. The aerodynamic and structural components are combined to form a closely coupled aeroelastic code that solves in the time-domain. The loading and thickness noise terms for the aeroacoustic calculations are calculated from the aerodynamic data using a formulation based on the Ffowcs Williams-Hawkings (FW-H) equation. The code is successfully validated for acoustic signature and BVI predictions using test cases from the HELINOISE program.

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Volume 109, Number 1096   June 2005

A novel approach to encouraging proper fatigue management in British Army aviation training and operations

Authors
R. P. King

Abstract
Fatigue management in military aviation remains problematic and can be easily neglected by planners and aircrew in a busy operational environment. The basic assessment tool (BAT) is an objective and educational computer tool for evaluating and combining various fatigue factors. It provides an impartial performance comparison while at the same time educating and reminding its users of the importance of fatigue management. Individual factors of the BAT were chosen because they affect fatigue, sleepiness, alertness and performance. A short explanation of components not chosen is also included. An example of how the BAT can be used is described and figures of the resulting outputs (screenshots) are included. Most commercial fatigue estimation products are subjective and do not consider specific issues associated with tactical operations in a field environment. This novel approach can be used to help plan missions by minimizing the BAT score while still maximising the tactical advantage and keeping fatigue management fresh in the minds of military rotary wing pilots while in training and on operations. Although the BAT is military aviation focused and objective, it can be easily modified to suit particular fatigue concerns.

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Volume 109, Number 1096   June 2005

Low frequency behaviour of the subsonic doublet lattice method

Authors
L. van Zyl

Abstract
The results of the subsonic doublet lattice method (DLM), i.e. generalised unsteady aerodynamic forces (GAFs) at a set of reduced frequencies, are often used as input to the solution of the flutter equation. Solutions of the flutter equation are usually required at many more reduced frequencies than GAFs are calculated for by the DLM and some form of interpolation is therefore required. In the p-k formulation of Rodden, Harder and Bellinger, the imaginary part of the GAFs appear as QI/k, i.e. the imaginary part of the GAFs divided by the reduced frequency. In the case of real (i.e. non-oscillatory) roots of the flutter equation, the solution is determined entirely by the steady GAFs and the limiting value of QI/k at zero frequency. This is also true of the g-method of flutter solution as the two formulations are equivalent at k = 0. Expressions are derived for calculating the limiting values of QI/k directly from the DLM, thereby making the real roots independent of the interpolation of the GAFs. The exact way in which the low frequency DLM results are interpolated has a small effect on the interpolation quality in the case of the p-k flutter equation, whereas it has a significant qualitative effect on the results of the g-method of flutter solution of Chen.

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Volume 109, Number 1097   July 2005

A Numerical study on mixing with air and hydrogen in scramjet combustor

Authors
M Ali and T Fujiwara

Abstract
A numerical study on mixing of air and hydrogen is performed by solving two-dimensional full Navier-Stokes equations. The main stream is air of Mach 5 entering through the configured inlet of the combustor and gaseous hydrogen is injected from the configured jet on the side wall. Supersonic mixing and diffusion mechanisms of a transverse hydrogen jet in two-dimensional finite air streams have been analyzed and discussed. The computed results are compared with the experimental data and show good agreement. For an otherwise fixed combustor geometry, the air inlet width and injection angle are varied to study the physics of mixing and flow field characteristics. On the effect of inlet width variation, two competing phenomena have been observed: (i) upstream of injector the strength of recirculation is higher for wider inlet and consequently the mixing increases, and (ii) downstream, the diffusion of hydrogen decreases with the increase of inlet width and eventually mixing decreases. As a result, in far downstream the mixing efficiency increases up to certain inlet width and then decreases for further increment of inlet width. For the variation of injection angle results show that upstream of injector the mixing is dominated by recirculation and downstream the mixing is dominated by mass concentration of hydrogen. Upstream recirculation is dominant for injecting angle 60° and 90°. Incorporating the various effects, perpendicular injection shows the maximum mixing efficiency and its large upstream recirculation region has a good flame holding capability.

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Volume 109, Number 1097   July 2005

Semi-optimal co-ordinated manoeuvres for aircraft conflict resolution

Authors
J. Parastari and M. B. Malaek

Abstract
In this manuscript, a new concept of 2D-semi-optimal-circular-3-arced-path manoeuvres with constant speed for multiple aircraft co-operative conflict resolution is presented. This type of manoeuvres is based on appropriate commands to heading, speed and manoeuvreing time. According to aircraft turning dynamics, each aircraft manoeuvre is composed of three tangent circular arcs. The optimality of manoeuvres is based on the minimisation of weighted sum of kinetic energy for aircraft two-legged manoeuvres. In comparison, aircraft with lower weight factors bear more responsibility to resolve the conflicts. The effectiveness of the proposed algorithm for real time conflict resolution is guaranteed, where the number of encountering aircraft is less than five. Otherwise, the current method could also be jointed to one of the fast resolution methods, like probabilistic resolution algorithm or genetic algorithm – as a tool to choose the convex domain – to become more computationally effective. Considerable number of case studies has been done to evaluate the effectiveness of the proposed methodology, while some are presented in the paper.

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Volume 109, Number 1097   July 2005

Computational fluid dynamics study of unconventional air vehicle configerations

Authors
R Ramamurti, W Sandberg, P Vaiana, J Kellogg and D Cylinder

Abstract
Two unconventional micro air vehicles developed by the Naval Research Laboratory are described. One of the vehicles employs flapping wings which is inspired by the flight of birds or insects but does not copy it directly. The second vehicle is a stop-rotor hybrid vehicle employing a pair of single blade, rotary/fixed wing panels, attached at their roots to separate coaxial shafts. An unstructured grid based incompressible flow solver, called feflo, is used to simulate the flow past these novel configurations in order to determine the flight characteristics of these vehicles.

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Volume 109, Number 1098   August 2005

Development of an airship for tropical rain

Authors
G. E. Dorrington

Abstract
The design, manufacture and testing of a 480 cubic metre helium-filled airship, or dirigible balloon, intended for flight above tropical rain forest canopy is outlined. The requirements for the airship and the preliminary sizing method are set-out. Details of the final design and flight test results are included, as well as suggestions concerning future work. Particular attention is paid to the issue of accurate station-keeping and operation close to the canopy with winds present. It is concluded that the development of a truly useful aerial platform for canopy biological studies requires further research in aerodynamics, dynamic simulation and ultra-quiet propulsion systems.

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Volume 109, Number 1098   August 2005

Bio-inspired design of flapping-wing micro air vehicles

Authors
K D Jones, C J Bradshaw, J Papadopoulos and M F Platxer

Abstract
In this paper the development and flight testing of flapping-wing propelled, radio-controlled micro air vehicles are described. The unconventional vehicles consist of a low aspect ratio fixed-wing with a trailing pair of higher aspect ratio flapping wings which flap in counterphase. The symmetric flapping-wing pair provides a mechanically and aerodynamically balanced platform, increases efficiency by emulating flight in ground effect, and suppresses stall over the main wing by entraining flow. The models weigh as little as 11g, with a 23cm span and 18cm length and will fly for about 20 minutes on a rechargeable battery. Stable flight at speeds between 2 and 5ms–1 has been demonstrated, and the models are essentially stall-proof while under power. The static-thrust figure of merit for the device is 60% higher than propellers with a similar scale and disk loading.

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Volume 109, Number 1098   August 2005

Studies of capacity estimation of the airport with two parallel runways

Authors
C Yihua, Y Chen and Y Zhou

Abstract
The analytical capacity models of an airport with two runways system are developed in this paper and the theoretical capacity curves yielded by this model are analysed. The statistic airport capacity estimation methodology based on historical data is introduced as well. Both analytical models and statistic strategy are applied to estimate the capacity of the two runways system of a typical airport. Two sets of airport capacity curves obtained in different ways are compared and analysed. The result of the analysis indicates that the mathematical model works effectively in a fairly accurate way in the estimation of airport capacity.

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Volume 109, Number 1098   August 2005

Effects of leading edge cross-sections on the aerodynamic characteristics for flow over non-slender delta wing

Authors
J Wang and S Lu

Abstract
The aerodynamic performances of a non-slender 50° delta wing with various leading-edge bevels were measured in a low speed wind tunnel. It is found that the delta wing with leading-edge bevelled leeward can improve the maximum lift coefficient and maximum lift to drag ratio, and the stall angle of the wing is also delayed. In comparison with the blunt leading-edge wing, the increment of maximum lift to drag ratio is 200%, 98% and 100% for the wings with relative thickness t/c = 2%, t/c = 6.7% and t/c = 10%, respectively.

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Volume 109, Number 1100   October 2005

Design of composite helicopter rotor blades to meet given cross-sectional properties

Authors
S. L. Lemanski, P. M. Weaver, G. F. J. Hill

Abstract
This paper examines the design of a composite helicopter rotor blade to meet given cross-sectional properties. As with many real-world problems, the choice of objective and design variables can lead to a problem with a non-linear and/or non-convex objective function, which would require the use of stochastic optimisation methods to find an optimum. Since the objective function is evaluated from the results of a finite element analysis of the cross section, the computational expense of using stochastic methods would be prohibitive. It is shown that by choosing appropriate simplified design variables, the problem becomes convex with respect to those design variables. This allows deterministic optimisation methods to be used, which is considerably more computationally efficient than stochastic methods. It is also shown that the design variables can be chosen such that the response of each individual cross-sectional property can be closely modelled by a linear approximation, even though the response of a single objective function to many design parameters is non-linear. The design problem may therefore be reformulated into a number of simultaneous linear equations that are easily solved by matrix methods, thus allowing an optimum to be located with the minimum number of computationally expensive finite element analyses.

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Volume 109, Number 1100   October 2005

Progress toward CFD for full flight envelope

Authors
E. N. Tinoco, D. R. Bogue, T-J. Kao, N. J. Yu, P. Li and D. N. Ball

Abstract
The value of computational fluid dynamics, CFD, delivered to date has mainly been related to its application to high-speed cruise design. To increase its applicability CFD must apply to the full flight envelope frequently characterised by large regions of separated flows. These flows are encountered by transport aircraft at low speed with deployed high lift devices, at their structural design loads conditions, or subjected to in-flight upsets that expose them to speed and/or angle-of-attack conditions outside the envelope of normal flight conditions to name a few. Such flows can only be characterised by the Navier-Stokes equations. This paper will report the progress toward CFD for full flight envelope. The CFD methods in use at Boeing will be described. Examples presented will address high-lift, loads and stability and control concerns including Reynolds scaling from wind tunnel to flight, vortex generator simulation, spoiler and horizontal tail effectiveness. In general, results shown are in ‘good enough’ agreement with experimental data. Deficiencies and the need for further algorithm and process improvement are noted. The need for automation to enable the large scale use of CFD will also be discussed.

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Volume 109, Number 1100   October 2005

The behaviour of circular synthetic jets in a laminar boundary layer

Authors
S. Zhong, F. Millet, and N. J. Wood

Abstract
Dye flow visualisation of circular synthetic jets was carried out in laminar boundary layers developing over a flat plate at a range of actuator operating conditions and freestream velocities of 0·05 and 0·1ms–1. The purpose of this work was to study the interaction of synthetic jets with the boundary layer and the nature of vortical structures produced as a result of this interaction. The effects of Reynolds number (Re), velocity ratio (VR) and Strouhal number (St) on the behaviour of synthetic jets were studied. At low Re and VR, the vortical structures produced by synthetic jets appear as highly stretched hairpin vortices attached to the wall. At intermediate Re and VR, these structures roll up into vortex rings which experience a considerable amount of tilting and stretching as they enter the boundary layer. These vortex rings will eventually propagate outside the boundary layer hence the influence of the synthetic jets on the near wall flow will be confined in the near field of the jet exit. At high Re and VR, the vortex rings appear to experience a certain amount of tilting but no obvious stretching. They penetrate the edge of the boundary layer quickly, producing very limited impact on the near wall flow. Hence it is believed that the hairpin vortices produced at low Re and VR are likely to be the desirable structures for effective flow separation control. In this paper, a vortex model was also described to explain the mechanism of vortex tilting.

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Volume 109, Number 1100   October 2005

PIV measurements in a twin-jet STOVL fountain flow

Authors
P. M. Cabrita, A. J. Saddington and K. Knowles

Abstract
Mean velocity and first order turbulence measurements were obtained from a three-dimensional upwash fountain flow generated by the impingement of two compressible axisymmetric turbulent jets onto a normal plane. The jet impingement area and fountain formation regions were examined with data obtained through the use of particle image velocimetry. Seven configurations with different nozzle pressure ratios were considered to ascertain the influence of jet compressibility on the fountain development. Results indicate that the mixing of the fountain is dependent on the nozzle pressure ratio, leading to an increase in the fountain spreading rate with increase in nozzle pressure ratio.

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Volume 109, Number 1100   October 2005

The birth of the practical aeroplane: An appraisal of the Wright Brothers achievements

Authors
G. D. Padfield and B. Lawrence

Abstract
In this second Aeronautical Journal paper providing a technical appraisal of the Wright brothers’ achievements, the authors use modelling and simulation and associated flight dynamics analysis to present the development of the first practical aeroplane. The aircraft in question, the Wright Flyer III, was deemed fit for service by the Wrights in October 1905, and had evolved significantly from the first powered aircraft of 17 December 1903. The appraisal tries to shed light on many of the flight handling problems that the Wright brothers faced during this, their third phase of aeronautical endeavour, in 1904 and 1905. They retained their unstable configuration born in the 1901 and 1902 gliders, gradually refining the performance and handling until they considered the aircraft was ready for market. Their process of refinement has been reconstructed in simulation within the Liverpool Wright project, highlighting the many important developments during a period when Wilbur and Orville’s own documentation was limited. Apart from their engineering excellence, the Wright brothers are to be acknowledged for their perseverance and resolve in overcoming setbacks, for their ability to innovate and to recover and learn from their mistakes. In many ways the Wright brothers represent a model for the modern aeronautical engineer, and it is hoped that their legacy will be better preserved through the documentation of this project.e

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Volume 109, Number 1101   November 2005

Normal shock wave/turbulent boundary-layer interaction control using ‘smart’ piezoelectric actuators

Authors
J. S. Couldrick, S. L. Gai, J. F. Milthorpe and K. Shankar

Abstract
This paper looks at active control of the normal shock wave/turbulent boundary layer interaction (SBLI) using smart flap actuators. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the bleed/suction rate through a plenum chamber. The cavity allows rapid thickening of the boundary-layer approaching the shock, which splits into a series of weaker shocks forming a lambda shock foot, thus reducing wave drag. Active control allows optimisation of the interaction, as it would be capable of either positioning the control region around the original shock position using a series of unimorph flaps or fixing the shock position by controlling the rate of mass transfer. The level of control achieved by unimorph piezoelectric actuators is not large because of small amounts of deflection possible. It is believed that to provide optimal control a piezoelectric material, which can provide greater strain and hence higher amounts of deflection is needed. However, currently such a piezoelectric material is not commercially available.

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Volume 109, Number 1101   November 2005

A civil aviation safety assessment model using a Bayesian belief network (BBN)

Authors
R. Greenberg, S. C. Cook and D. Harris

Abstract
In this paper we present a Bayesian belief network (BBN) socio-technical model for investigating the accident rate for multi-crew civil airline aircraft. The model emphasises the influence of airline policy and societal behaviour patterns on the pilots within the piloting system. The main claim of this paper is that a BBN can be used to bring most aviation safety-critical elements into a common quantitative safety assessment despite the unique problems posed by the very low probability of accidents. We support this claim by replicating certain phenomena such as the low accident rate, the difference between the ‘more’ and ‘less’ safe airlines and other statistical factors of civil aviation. In particular, the model succeeds in explaining the large gap of six to seven orders of magnitude between in-flight measurements of pilots’ error and accident rate.

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Volume 109, Number 1101   November 2005

Shock-wave induced instability in

Authors
A. Bagabir and D. Drikakis

Abstract
The paper presents an investigation of flow instabilities occurring in shock-wave propagation and interaction with the walls of an enclosure. The shock-wave propagation is studied in connection with perturbed and unperturbed cylindrical blasts, initially placed in the centre of the enclosure, as well as for three different blast intensities corresponding to Mach numbers Ms = 2, 5 and 10. The instability is manifested by a symmetry-breaking of the flow even for the case of an initially perfectly-symmetric blast. It is shown that the symmetry-breaking initiates around the centre of the enclosure as a result of the interaction of the shock waves reflected from the walls, with the low-density region in the centre of the explosion. The instability leads to fast attenuation of the shock waves, especially for smaller initial blast intensities. The computations reveal that the vortical flow structures arising from the multiple shock reflections and flow instability are Mach number dependent. The existence of perturbations of large amplitude in the initial condition strengthens the instability and has significant effects on the instantaneous wall pressure distributions. The computational investigation has been performed using high-resolution Riemann solvers for the gas dynamic equations.

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Volume 109, Number 1101   November 2005

A theoretical description of viscous flow along a flat plate

Authors
R. C. Hastings

Abstract
Theoretical quantification of viscous effects in fluid flows is difficult, even if turbulence is absent, except when it is legitimate to simplify the Navier-Stokes equations in some way; for example by invoking the boundary-layer approximation in appropriate cases of interacting viscous and inviscid flow. The technical importance of viscous effects was thought sufficient incentive to re-examine a very simple flow configuration – namely plane, uniform and steady flow of an incompressible, viscous fluid toward a vanishingly-thin flat plate aligned with the undisturbed stream – in search of fresh insights into the general theory for viscous-inviscid interactions.
The strategy was to exploit the analogy between vorticity transport in a viscous fluid and heat conduction in a moving solid. The key to doing so was the realization that, if the perturbation of the undisturbed flow by the plate might be represented as the sum of a series of successive approximations, then the stream function of the viscous part o

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Volume 109, Number 1102   December 2005

Status and perspectives of laminar flow

Authors
G. Schrauf

Abstract
After identifying the ecological and economic drivers for use of laminar flow technology, we outline the mechanisms of laminar-turbulent boundary layer transition and review the status of natural laminar flow (NLF) and hybrid laminar flow control (HLFC). New ways to reduce the complexity of HLFC systems are presented, and the remaining steps to achieve technology readiness are discussed.

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Volume 109, Number 1102   December 2005

Optimum design for buckling of arbitrary shaped ribs under uncertain loadings

Authors
A. C. Conrado, A. R. de Faria and S. F. M. de Almeida

Abstract
Typically, aircraft wing structural panels are designed against buckling for a very large number of possible loadings that may occur during the operation of the aircraft. If the optimisation procedure accounts only for a limited number of design loads, the structure may be vulnerable to a specific type of loading that may cause the structure to fail. A novel approach for the optimisation of ribs or plates of arbitrary shapes under uncertain loads is proposed. The geometry of the rib is defined by a single closed spline or several connected splines. The loading distribution is not considered to be uniform but it is allowed to vary within an admissible set, conferring uncertainty to the applied loads. The admissible load space comprises distributed normal and shear loadings that can be represented through a collection of piecewise linear functions defined along the plate boundary. A special procedure is applied to handle the constraint that the loading must be self equilibrating. A minimax strategy is used to deal with the loading variability such that the resulting optimal design is able to withstand an entire class of linear piecewise loadings along the rib boundary. The refinement of the loading representation may be completely independent of the refinement of finite element mesh. The validity of the proposed approach is assessed by applying it to an aeronautical wing rib.

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Volume 109, Number 1102   December 2005

Prediction of acoustic resonance phenomena for weapon bays using detached eddy simulation

Authors
R. M. Ashworth

Abstract
It is argued that acoustic resonance phenomena in open cavities such as weapons bays cannot be adequately predicted through numerical solution of Reynolds averaged Navier-Stokes (RANS) equations. The requirement to resolve the growth of the shear layer instability from the lip of the cavity inevitably implies that turbulence further downstream is resolved while also being modelled thus making RANS over dissipative. Large eddy simulation (LES) models only unresolved scales and a hybrid method combining RANS near walls with LES in the cavity appears a practical alternative to pure RANS. This paper compares computations of the M219 cavity configuration made with unsteady RANS and with the hybrid method known as detached eddy simulation (DES). It is shown that whilst unsteady RANS and DES give very similar predictions for the 1st and 3rd modes of the acoustic resonance the 2nd mode (which is dominant near the centre of the cavity) is absent in the RANS results but well predicted by DES. The 2nd mode is thought to arise from an interaction with vortical structures in the shear layer which are suppressed in the highly dissipative RANS method. The 4th mode, which is much weaker than the other three modes, is over-predicted by DES and under-predicted by a smaller amount in RANS.

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Volume 109, Number 1102   December 2005

Solar-powered space flight

Authors
M. H. D. Kemp

Abstract
The aim of this paper is analyse the practicality or otherwise of solar-powered propulsion (after launch using conventional chemical rocketry) for a space vehicle’s late pre-orbital trajectory phase, for orbital transfer and for post-orbital flight. We introduce a ‘concept’ vehicle that in principle permits the use of solar-powered propulsion in each of these stages. Some of the technical challenges that such a vehicle might face are analysed, including the problem of how to keep a large ultra-low mass optical concentrator arrangement sufficiently accurately positioned in different parts of such a trajectory.

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Volume 109, Number 1102   December 2005

Dynamic gain-scheduled control of the ICE 101-TV

Authors
C. D. C. Jones, T. S. Richardson and M. H. Lowenberg

Abstract
This paper shows the theoretical development and application of dynamic gain scheduled control – a novel method for the control of nonlinear systems – to an aircraft model. The idea behind this method is to schedule the control law gains with a fast varying state variable rather than with a slow varying state or an input parameter. This is advantageous as it is then possible to schedule the gains with a state variable that is dominant in the mode that we are most interested in controlling. The use of this type of gain scheduling is shown to improve the transient response of the aircraft model when stepping between trim conditions and to overcome some of the problems associated with conventional gain scheduled controllers (such as control surface position limit saturation). ‘Hidden coupling terms’ that introduce unwanted dynamics when scheduling gains with a fast state (rather than the input design parameter) are eliminated directly by applying a transformation to the classical parameter-scheduled gain distributions which are calculated using eigenstructure assignment. A second order longitudinal model and a 5th order longitudinal/lateral model of the ICE 101-TV tailless delta-wing aircraft configuration are used to demonstrate the design process.

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Volume 110, Number 1103   January 2006

CFD Fire simulation of the Swissair flight 111 In-flight fire - Part1: Prediction of the pre-fire Air flow within the cockpit and surrounding areas

Authors
E Galea

Abstract
The SMARTFIRE computational fluid dynamics (CFD) software was used to predict the ‘possible’ behaviour of airflow as well as the spread of fire and smoke within a Swissair configured McDonnell Douglas MD-11 commercial transport aircraft. This work was undertaken by the Fire Safety Engineering Group (FSEG) of the University of Greenwich as part of Transportation Safety Board (TSB) of Canada, Fire & Explosion Group’s investigation into the in-flight fire occurrence onboard Swissair Flight 111 (SR111): TSB Report Number A98H0003. The main aims of the CFD analysis were to develop a better understanding of the possible effects, or lack thereof, of numerous variables relating to the in-flight fire. This assisted investigators in assessing possible fire dynamics for cause and origin determination. In Part 1, the numerical analyses to pre-fire airflow patterns within the cockpit and its vicinity are presented. The pre-fire simulations serve two ends. One is to provide insight into the flow patterns within the cockpit and its vicinity and further supportive numerical evidence for the airflow flight test observations. The other is to provide plausible initial flow conditions for fire simulations. In this paper, some flow patterns at a number of primary locations within the cockpit and its vicinity are highlighted and the predicted flow patterns are compared with the findings from the airflow flight tests. The predicted patterns are found to be in good qualitative agreement with the experimental test findings.

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Volume 110, Number 1103   January 2006

Modern developments in hypersonic wind tunnels

Authors
R. J. Stalker

Abstract
The development of new methods of producing hypersonic wind- tunnel flows at increasing velocities during the last few decades is reviewed with attention to airbreathing propulsion, hypervelocity aerodynamics and superorbital aerodynamics. The role of chemical reactions in these flows leads to use of a binary scaling simulation parameter, which can be related to the Reynolds number, and which demands that smaller wind tunnels require higher reservoir pressure levels for simulation of flight phenomena. The use of combustion heated vitiated wind tunnels for propulsive research is discussed, as well as the use of reflected shock tunnels for the same purpose. A flight experiment validating shock-tunnel results is described, and relevant developments in shock tunnel instrumentation are outlined. The use of shock tunnels for hypervelocity testing is reviewed, noting the role of driver gas contamination in determining test time, and presenting examples of air dissociation effects on model flows. Extending the hypervelocity testing range into the superorbital regime with useful test times is seen to be possible by use of expansion tube/tunnels with a free piston driver.

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Volume 110, Number 1103   January 2006

Modelling the flight dynamics of the hang glider

Authors
M V Cook and M Spottiswoode

Abstract
The development of the non-linear equations of motion for the hang glider from first principles is described, including the complex geometry of control by pilot ‘weight shift’. By making appropriate assumptions the linearised small perturbation equations are derived for the purposes of stability and control analysis. The mathematical development shows that control is effected not by pilot weight shift, but by centre of gravity shift and that lateral-directional control by this means is weak, and is accompanied by significant instantaneous adverse response. The development of a comprehensive semi-empirical mathematical model of the flexible wing aerodynamics is described. In particular, the modelling attempts to quantify camber and twist dependencies. The performance of the model is shown to compare satisfactorily with measured hang glider wing data obtained in earlier full scale experiments. The mathematical aerodynamic model is then used to estimate the hang glider stability and control derivatives over the speed envelope for substitution into the linearised equations of motion. Solution of the equations of motion is illustrated and the flight dynamics of the typical hang glider are described. In particular, the dynamic stability properties are very similar to those of a conventional aeroplane, but the predicted lateral directional stability margins are significantly larger. The depth of mathematical modelling employed enables the differences to be explained satisfactorily. The unique control properties of the hang glider are described in some detail. Pitch and roll control of the hang glider is an aerodynamic phenomenon and results from the pilot adjusting his position relative to the wing in order to generate out of trim aerodynamic control moments about the centre of gravity. Maximum control moments are limited by hang glider geometry which is dependent on the length of the pilot’s arm. The pilot does not generate control moments directly by shifting his weight relative to the wing. The modelling thus described would seem to give a plausible description of the flight dynamics of the hang glider.

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Volume 110, Number 1103   January 2006

A feasiblity study on designing model support systems for a blended wing body configuration in a transonic wind tunnel

Authors
M. Maina, N. Corby, E. L. Crocker, P. J. Hammond and P. W. C. Wong

Abstract
It is considered that the blended wing body may offer the possibility of improvements in performance efficiency over the conventional civil transport. Such configurations will require transonic wind tunnel testing. Hence, a feasibility study has been carried out at ARA to investigate possible model support systems that could be used for this purpose. The study addressed issues arising from the mechanical design of two support systems; namely, a blade or Z-sting and a standard rear sting. In particular, the relatively restricted space available within the model fuselage has presented challenges in the design of the layout of the balance and instrumentation required for the model. CFD analysis has been carried out to assess the relative interference effects of the two support arrangements. This initial work has shown unexpectedly significant interference effects associated with the Z-sting support and attention is drawn to the need for further design work to minimise these effects.

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Volume 110, Number 1103   January 2006

Comparison of a grid-based CFD method and vortex dynamics predictions of low Reynolds number cylinder flows

Authors
L. Baranyi and R. I. Lewis

Abstract
Computational fluid dynamics models range from the finite difference type grid-based method to the Lagrangian style vortex cloud simulation technique for solving the Navier-Stokes equations. This paper undertakes a comparison of these two methods for the classical datum bluff body case of flow past a stationary circular cylinder at low Reynolds numbers in the range 10 to 220. Comparisons include time-history, time-mean and root-mean-square values of oscillating drag and lift coefficients, frequency of vortex shedding and related vortex street wake flow patterns. Particularly close agreement was obtained for Strouhal number versus Reynolds number, and good agreement for time-mean value of drag coefficients; comparison was also made with experimental results. Attempts are also made to calculate the skin friction and surface pressure components of the cylinder drag, revealing the significance of skin friction drag within this range and its relative insignificance above a Reynolds number of 220.

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Volume 110, Number 1104   February 2006

On the vortex created by multiple blades joined at a hub

Authors
P. R. Spalart

Abstract
Experimental studies often use several blades, joined on the centreline, to generate a vortex in a wind tunnel. The circulation profile of this vortex is non-trivial, and a rapid prediction method will facilitate the design of such devices. Prompted by an experiment of Beninati and Marshall, such a model was derived. It assumes a large number of narrow blades and small turning angles, and rests on a balance of angular momentum and on simple aerofoil function. It is claimed to be valid even close to the centreline, can be completed analytically, contains no adjustable constants, and agrees well with two experiments although the turning angle reached 16° and the devices only had two or four blades. With typical geometries, the interference between blades makes the circulation profile quite different from that behind an elliptically-loaded wing, prompting some doubt over the relevance of such a vortex to those trailing real wings.

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Volume 110, Number 1104   February 2006

Autonomy in unmanned air vehicles

Authors
J. T. Platts

Abstract
The paper describes a key risk area threatening the widespread deployment of unmanned air vehicles (UAVs), that of attaining high levels of autonomy. Autonomy is loosely defined in the context of UAVs and the meaning of ‘level of autonomy’ discussed. The paper argues that the achievement of high levels of autonomy is not merely a function of increasing machine intelligence but also of maintaining the human operator’s engagement with the decision making process and retaining human authority. An assumption is that a human being in the loop will be a requirement for safety, flight clearance and legal reasons on early systems. Therefore, developers of highly autonomous systems are presented with a paradox. It will be argued that the human must be placed at the centre of the design process and consequently human factors, the human machine interface and the system architecture become critical to achieving high levels of autonomy. This quality impacts on the entire knowledge acquisition and design cycle and broadens what is meant by that term placing it as a discipline firmly in the systems design community. The paper concludes by outlining the key barriers to the successful development of highly autonomous UAVs.

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Volume 110, Number 1104   February 2006

Predicting design induced pilot error using HET (human error template)

Authors
N A Stanton, D Harris, P M Salmon, J M Demagalski, A. Marshall, M S Young and S W A Dekker

Abstract
Human factors certification criteria are being developed for large civil aircraft with the objective of reducing the incidence of design-induced error on the flight deck. Many formal error identification techniques currently exist which have been developed in non-aviation contexts but none have been validated for use to this end. This paper describes a new human error identification technique (HET – human error template) designed specifically as a diagnostic tool for the identification of design-induced error on the flight deck. HET is benchmarked against three existing techniques (SHERPA – systematic human error reduction and prediction approach; human error HAZOP – hazard and operability study; and HEIST – human error In systems tool). HET outperforms all three existing techniques in a validation study comparing predicted errors to actual errors reported during an approach and landing task in a modern, highly automated commercial aircraft. It is concluded that HET should provide a useful tool as a adjunct to the proposed human factors certification process.

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Volume 110, Number 1104   February 2006

BAE Systems/EPSRC integrated research programme in aeronautical engineering

Authors
N. McDougall

Abstract
BAE Systems and the Engineering and Physical Sciences Research Council (EPSRC) have recently formed a partnership to invest in strategic research in aerospace and defence. The framework which has been developed as part of this new alliance places a strong emphasis on collaboration. This contrasts with the conventional approach to industry led research which is normally based on the establishment of ‘centres of excellence’ in specific subject areas. By using a collaborative approach, the funding partners aim to benefit from inter-disciplinary collaboration which will take place during the project, giving rise to a more effective use of the invested funds. The objective of the research programme is to develop technologies which would support the design of low cost (both to acquire and operate) flapless unmanned aerial vehicles (UAVs). This work includes fundamental aerodynamic research to provide control forces without the use of conventional flaps, coupled with developments in the areas of control systems, manufacturing engineering, structural engineering, the electromagnetic behaviour of these structures and design optimisation. The output from the research has been extended to include the design, manufacture, assembly and flight of a demonstrator vehicle, which will provide the research teams with a platform on which to evaluate the performance of their technology in a realistic flight environment. A total of fourteen research groups at ten universities are involved in the five year programme, which has a total value of £6×5M (€9×75M).

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Volume 110, Number 1104   February 2006

A continuation design framework for nonlinear flight control problems

Authors
T. S. Richardson and M. H. Lowenberg

Abstract
A methodology referred to as the continuation design framework is developed for application to nonlinear flight control problems. This forms the basis of a systematic approach to control system design for aircraft operating in highly nonlinear regions of the flight envelope. The essence of the continuation design framework is to combine bifurcation analysis with modern control methods such as eigenstructure assignment. Theoretical and practical issues of the approach are discussed with particular reference to the problems posed by agile fighter aircraft. The proposed methodology is applied to a fifth order hypothetical aircraft model and is shown to provide a visible, flexible and logical approach to nonlinear aircraft control law design.

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Volume 110, Number 1105   March 2006

A dynamic sampling scheme for GPS

Authors
S. Feng and W. Ochieng, D. Walsh and R. Ioannides

Abstract
The Global Positioning System (GPS) is already being used for certain aviation applications and some safety critical air traffic services will be based on GPS. These air traffic services must achieve allowable levels of safety before they can be accepted. For this to occur, GPS based navigation systems must achieve a defined level of performance specified in terms of accuracy, integrity, continuity and availability. This must be determined by various analysis techniques including failure mode and effects analysis (FMEA) and integrity assessment. Because of the high percentile requirements placed on integrity (as the parameter most directly related safety), it is unfeasible to measure system performance by demonstration (field trial). Realistic simulation informed by some field experience is usually employed. However, the current simulation-based approaches for receiver autonomous integrity monitoring (RAIM) performance assessment have a number of weaknesses including the use of coarse (large) spatial and temporal sampling intervals, loose definitions of error and geometric correlations, a lack of sampling of all geometries and the inability to account for critical points due to uncorrelated factors. This paper proposes a dynamic sampling method that takes account of these weaknesses, identifying dynamically only the required points for integrity performance assessment. Comprehensive simulations carried out to test the proposed approach for a single point, an area, and a non-precise approach (NPA) flight path to Gatwick airport in the United Kingdom show that the method can be effective in capturing all the points enabling a robust and reliable assessment of system integrity.

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Volume 110, Number 1105   March 2006

The development of a target-lock-on optical remote sensing system for unmanned aerial vehicles

Authors
F-B Hsiao, T-L Liu, Y-H Chien, M-T Lee and R. Hirst

Abstract
The use of unmanned aerial vehicles (UAVs) in various military and civil applications is the subject of much current attention. With recent developments in personal computer technology, and the availability at affordable cost of peripherals, and electronic and optical sensors, UAVs for long endurance missions, with flight autonomy beyond the visual range, have become an attractive challenge for study in universities and research institutes. This paper describes the development of a target-lock-on optical remote sensing system to be used as a payload in a university-class UAV. To accomplish autonomous way-point navigation for the conduct of optical sensing surveillance, a gimbaled-platform with servo control and an Attitude and Heading Reference System (AHRS) navigation system for UAV position and attitude measurements have been developed. The UAV also utilises a Global Position System (GPS) receiver, a pressure altimeter, gyroscopes and an electric compass. A novel mathematical model is proposed to calculate the optimal parameters for orientating the CCD camera line of sight with a ground target, designated in real time from a ground control station. Both ground and flight test results have demonstrated the feasibility of the navigation control scheme and the UAV’s ability to conduct ground target acquisition and image transmission.

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Volume 110, Number 1105   March 2006

A dynamic sampling scheme for GPS

Authors
S. Feng, W. Ochieng, D. Walsh and R. Ioannides

Abstract
The Global Positioning System (GPS) is already being used for certain aviation applications and some safety critical air traffic services will be based on GPS. These air traffic services must achieve allowable levels of safety before they can be accepted. For this to occur, GPS based navigation systems must achieve a defined level of performance specified in terms of accuracy, integrity, continuity and availability. This must be determined by various analysis techniques including failure mode and effects analysis (FMEA) and integrity assessment. Because of the high percentile requirements placed on integrity (as the parameter most directly related safety), it is unfeasible to measure system performance by demonstration (field trial). Realistic simulation informed by some field experience is usually employed. However, the current simulation-based approaches for receiver autonomous integrity monitoring (RAIM) performance assessment have a number of weaknesses including the use of coarse (large) spatial and temporal sampling intervals, loose definitions of error and geometric correlations, a lack of sampling of all geometries and the inability to account for critical points due to uncorrelated factors. This paper proposes a dynamic sampling method that takes account of these weaknesses, identifying dynamically only the required points for integrity performance assessment. Comprehensive simulations carried out to test the proposed approach for a single point, an area, and a non-precise approach (NPA) flight path to Gatwick airport in the United Kingdom show that the method can be effective in capturing all the points enabling a robust and reliable assessment of system integrity.

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Volume 110, Number 1105   March 2006

Benefits and design challenges of adaptive structures for morphing aircraft

Authors
D. Moorhouse, B. Sanders, M. von Spakovsky and J. Butt

Abstract
The purpose of this paper is to discuss the future of adaptive structures leading towards the concept of a fully morphing aircraft configuration. First, examples are shown to illustrate the potential system-level mission benefits of morphing wing geometry. The challenges of design integration are discussed along with the question of how to address the optimisation of such a system. This leads to a suggestion that non-traditional methods need to be developed. It is suggested that an integrated approach to defining the work to be done and the energy to be used is the solution. This approach is introduced and then some challenges are examined in more detail. First, concepts of mechanisation are discussed as ways to achieve optimum geometries. Then there are discussions of non-linearities that could be important. Finally, the flight control design challenge is considered in terms of the rate of change of the morphing geometry. The paper concludes with recommendations for future work.

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Volume 110, Number 1106   April 2006

Numerical calculation of separated flow past square and rectangular cylinders using panel technique

Authors
A Roy and G. Bandyopadhyay

Abstract
In the present investigation, a potential flow model based on panel method has been developed for calculation of two dimensional separated flows past square and rectangular cylinders. Free vortex lines are assumed to emanate from the points of separation that converge downstream of the body. The converged wake shape is iteratively obtained by integrating the velocity vectors at the collocation points. For solving separated flow past square and rectangular cylinders, four different versions of the solver have been developed for a wide range of incidence, namely, for zero, low, moderate and high angles of incidence. For validation of computed results, experimental investigations have been carried out in a low speed wind tunnel to obtain the surface pressure distribution on square cylinder and rectangular cylinder over a range of angles of incidence. Comparison is reasonably good.

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Volume 110, Number 1106   April 2006

Impact of privatisation on the financial and economic performance of European airports

Authors
Dr H.-A. Vogel

Abstract
This paper assesses the financial performance of 35 European airports for the decade 1990 to 2000, comparing those subject to partial or full privatisation with those still in public ownership. In contrast to earlier research, the outcomes of partial factor productivity (PFP), financial ratio (FRA) and data envelopment analysis (DEA) are evaluated, in order to investigate differences attributable to the degree of privatisation. Changes in performance after a change in ownership structure are reviewed. The analysis of sample data reveals economically meaningful and statistically significant differences between publicly owned and privatised airports. The major differences lie in operating efficiency, capital productivity and capital structure. Although partially and fully privatised airports operate more efficiently, this does not translate into significantly higher returns on shareholders’ funds. Due to their at least indirectly government-backed credit standing, publicly owned airport companies can assume more debt relative to their respective equity. This results in considerably higher gearing and financial leverage, which compensates for the comparatively low return rate on assets.

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Volume 110, Number 1106   April 2006

An analysis of exit availability, exit usage and passenger exit selection behaviour exhibited during actual aviation accidents

Authors
E. R. Galea, K. M. Finney, A. J. P. Dixon, A. Siddiqui and D. P. Cooney

Abstract
The exits which passengers select in evacuation situations and the exits which are available post-crash is of great interest to aviation safety regulators who make rulings defining exit separation and aircraft evacuation certification, aircraft designers who develop the interior layout of aircraft cabins and position exits within the fuselage, cabin safety specialists who develop procedures for managing aircraft evacuation and cabin crew who must control aircraft evacuations. In this paper we examine issues associated with passenger exit selection behaviour and exit configurations frequently experienced during survivable crashes. This work makes use of the latest version of the Aircraft Accident Statistics and Knowledge database AASK V4.0, which contains information from 105 survivable crashes and over 2,000 survivors.

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Volume 110, Number 1106   April 2006

Corporate memory contribution to integrated design and analysis systems

Authors
M. R. Mendenhall

Abstract
The recent decline in the USA aerospace industry has resulted in fewer programs, fewer engineers, and a potential loss of capability for future technology development. As engineers retire or leave the industry, their corporate memory or retained knowledge must be preserved for future use. A process to capture their expert knowledge is described, and a framework which provides a means to retrieve and use this valuable technical information is shown. Four examples of integrated design and analysis systems for four diverse technologies and applications are discussed.

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Volume 110, Number 1107   May 2006

CFD fire simulation of the Swissair Flight 111 in-flight fire – Part II: Fire spread analysis

Authors
F. Jia, M. K. Patel, E. R. Galea, A. Grandison and J. Ewer

Abstract
In 1998, Swissair Flight 111 (SR111) developed an in-flight fire shortly after take-off which resulted in the loss of the aircraft, a McDonnell Douglas MD-11, and all passengers and crew. The Transportation Safety Board (TSB) of Canada, Fire and Explosion Group launched a four year investigation into the incident in an attempt to understand the cause and subsequent mechanisms which lead to the rapid spread of the in-flight fire. As part of this investigation, the SMARTFIRE Computational Fluid Dynamics (CFD) software was used to predict the ‘possible’ development of the fire and associated smoke movement. In this paper the CFD fire simulations are presented and model predictions compared with key findings from the investigation. The model predictions are shown to be consistent with a number of the investigation findings associated with the early stages of the fire development. The analysis makes use of simulated pre-fire airflow conditions within the MD-11 cockpit and above ceiling region presented in an earlier publication (Part I) which was published in The Aeronautical Journal in January 2006(4).

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Volume 110, Number 1107   May 2006

Aeroelastic analysis through linear and non-linear methods: a summary of flutterprediction in the PUMA DARP

Authors
N. V. Taylor, C. B. Allen, A. L. Gaitonde, D. P. Jones, G. A . Vio, J. E. Cooper, A. M. Rampurawala, K. J. Badcock, M. A. Woodgate, M. J. de C. Henshaw

Abstract
This paper presents a comparison of linear and non-linear methods for the analysis of aeroelastic behaviour and flutter boundary prediction. The methods in question include NASTRAN and ZAERO, based on linear aerodynamics, and the non-linear coupled CFD-CSD methods RANSMB and PMB, developed at the Universities of Bristol and Glasgow respectively. The test cases used for this comparison are the MDO and AGARD 445.6 weakened wing. In general, it was found that the non-linear methods demonstrate excellent agreement with respect to pressure distributions, deflections, dynamic behaviour, and flutter boundary locations for both cases. This is in contrast to previous studies involving similar methods, where notable differences across the MDO span were found, and is taken to imply good performance of the CFD-CSD interpolation schemes employed here. While the linear methods produce similar flutter boundaries to the coupled codes for the aerodynamically simple AGARD 445.6 wing, results for the transonic ‘rooftop’ MDO wing design did not agree as well.

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Volume 110, Number 1107   May 2006

Key aerodynamic technologies for aircraft engine nacelles

Authors
S. Raghunathan, E. Benard, J. K. Watterson, R. K. Cooper, R. Curran, M. Price, H. Yao, R. Devine and B. Crawford, D. Riordan, A. Linton, J. Richardson and J. Tweedie

Abstract
Customer requirements and vision in aerospace dictate that the next generation of civil transport aircraft should have a strong emphasis on increased safety, reduced environmental impact and reduced cost without sacrificing performance. In this context, the School of Mechanical and Aerospace Engineering at the Queen’s University of Belfast and Bombardier have, in recent years, been conducting research into some of the key aerodynamic technologies for the next generation of aircraft engine nacelles. Investigations have been performed into anti-icing technology, efficient thrust reversal, engine fire zone safety, life cycle cost and integration of the foregoing with other considerations in engine and aircraft design. A unique correlation for heat transfer in an anti-icing system has been developed. The effect of normal vibration on heat transfer in such systems has been found to be negligible. It has been shown that carefully designed natural blockage thrust reversers without a cascade can reduce aircraft weight with only a small sacrifice in the reversed thrust. A good understanding of the pressure relief doors and techniques to improve the performance of such doors have been developed. Trade off studies between aerodynamics, manufacturing and assembly of engine nacelles have shown the potential for a significant reduction in life cycle cost.

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Volume 110, Number 1107   May 2006

EPISTLE: High lift system design for

Authors
U. Herrmann

Abstract
A new approach for low-drag high-lift system design based on the application of viscous flow solvers was developed in the EC research project EPISTLE. Two high-lift systems for a supersonic commercial transport aircraft (SCT) wing were designed, manufactured and wind-tunnel tested. The predicted large drag reductions were fully confirmed by tests at high Reynolds numbers. These drag reductions significantly reduce the low-speed noise of future SCT configurations. This was estimated by preliminary aircraft design tools. Low-speed noise reduction by aerodynamic means is obtained, as effective high-lift systems enable these aircraft to climb faster.

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Volume 110, Number 1107   May 2006

Rigid body separation dynamics for space launch vehicles

Authors
B. N. Rao, D. Jeyakumar, K. K. Biswas, S. Swaminathan and E. Janardhana

Abstract
This paper presents a systematic formulation for the simulation of rigid body dynamics, including the short period dynamics, inherent to stage separation and jettisoning parts of a satellite launcher. This also gives a review of various types of separations involved in a launch vehicle. The problem is sufficiently large and complex; the methodology involves iterations at successively lower levels of abstraction. The best choice to tackle such problems is to use state-of-the-art programming technique known as object oriented programming. The necessary classes have been identified to represent various entities in the launch vehicle separation process (e.g., gravity, aerodynamics, propulsion and separation mechanisms etc.). Simple linkages are modelled with suitable objects. This approach helps the designer to simulate a launch vehicle separation dynamics and also to analyse separation system performance. To examine the influence of the design variables on the separating bodies, statistical analyses have been performed on the upper stage separation process and pull out of ongoing stage nozzle from the spent stage of a multistage rocket carrier using retro rockets.

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Volume 110, Number 1108   June 2006

Development of an aircraft systems dispatch reliability design methodology

Authors
M. Bineid and J. P. Fielding

Abstract
This paper describes the development of a generic aircraft systems dispatch reliability design methodology (ASDRDM) that has been developed for use during early phases of the aircraft systems design process. The methodology incorporates prediction of both reliability and maintainability through the aircraft design hierarchy, down to component level. It can be applied at the early design stage, but can also be used for advanced design phases and can use generic or actual failure rate and mean time to repair data. It allows designers to modify system architectures and component reliability and maintainability characteristics. The paper shows the validation that has been performed, and its use is demonstrated by a case-study.

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Volume 110, Number 1108   June 2006

Experimental Investigations on the Application of Lift Enhancement Devices to Forward-Swept Aircraft

Authors
Zhang W , Wang J, J and Wu Z

Abstract
The force measurements were conducted in low speed wind tunnel to investigate the effects of the scale, shape and the installation type of Gurney flap on a forward-swept aircraft model. The results indicated that both rectangular and triangular Gurney flaps can enhance the lift coefficient of the model tested, but with a little decrease of stall angle from 38° to 36°. The lift and drag coefficients increased with the Gurney flap scales. Meanwhile, the triangular Gurney flap can improve the aerodynamic performance more effectively when its high side is located near the wing root than the reverse installation with the low side near the wing root and the high side near the wing tip. Additionally, for the same Gurney flap, the model with smaller forward-swept angle can generate higher lift-enhancement in comparison with the larger forward-swept angle model.

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Volume 110, Number 1108   June 2006

Minimum forebody drag in hypersonic continuum and rarefied flows

Authors
J Pike

Abstract
Minimum drag shapes of given length and base area are investigated for hypersonic flow using both Newtonian impact theory and free molecular flow theory. The drag of Newton’s minimum drag body, which has previously been evaluated by numerical means, is derived as an analytic expression. The analytical results are applicable to a range of local pressure laws allowing minimum drag shapes obtained using impact theory to be directly compared with low density flow equivalents using free molecular flow. The low density shapes are found to have larger blunt regions at the nose and significantly larger drag coefficients. For free molecular flow the drag varies with the surface reflection characteristics. As the fraction of diffuse reflection at the surface increases, the drag increases and the sensitivity of the drag to changes in the minimum drag shape is reduced.

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Volume 110, Number 1108   June 2006

The performance of round synthetic jets in quiescent flow

Authors
M. Jabbal, J. Wu and S. Zhong

Abstract
PIV measurements in the near-field region of a jet flow emanating from a round synthetic jet actuator into quiescent air were conducted over a range of operating conditions. The primary purpose of this work was to investigate the nature of synthetic jets at different operating conditions and to examine the jet flow parameters that dictate the behaviour of synthetic jet actuators. The effects of varying diaphragm displacement and oscillatory frequency for fixed actuator geometry were studied. It was observed that the characteristics of synthetic jets are largely determined by the Reynolds number and stroke length. An increase in the former is observed to increase the strength of consecutive vortex rings that compose a synthetic jet, whereas an increase in the latter results in an increase in relative vortex ring spacing and for further increases in stroke length, shedding of secondary vortices. Correlations were also made between the operating parameters and the performance parameters most effective for flow control and which therefore determine the impact of a synthetic jet on an external flow. Relations of time-averaged dimensionless mass flux, momentum flux and circulation with the jet flow conditions were established and found to widely support an analytical performance prediction model described in this paper. It is anticipated that the experimental data obtained in this study will also contribute towards providing a PIV database for macro-scale synthetic jet actuators.

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Volume 110, Number 1108   June 2006

Cumulative global metamodels with uncertainty – a tool for aerospace integration

Authors
P. H. Reisenthel, J. F. Love, D. J. Lesieutre and R. E. Childs

Abstract
The integration of multidisciplinary data is key to supporting decisions during the development of aerospace products. Multidimensional metamodels can be automatically constructed using limited experimental or numerical data, including data from heterogeneous sources. Recent progress in multidimensional response surface technology, for example, provides the ability to interpolate between sparse data points in a multidimensional parameter space. These analytical representations act as surrogates that are based on and complement higher fidelity models and/or experiments, and can include technical data from multiple fidelity levels and multiple disciplines. Most importantly, these representations can be constructed on-the-fly and are cumulatively enriched as more data become available. The purpose of the present paper is to highlight applications of these cumulative global metamodels (CGM), their ease of construction, and the role they can play in aerospace integration. A simple metamodel implementation based on a radial basis function network is presented. This model generalises multidimensional data while simultaneously furnishing an estimate of the uncertainty on the prediction. Four examples are discussed. The first two illustrate the efficiency of surrogate-based design/optimisation. The third applies CGM concepts to a data fusion application. The last example is used to visualise extrapolation uncertainty, based on computational fluid dynamics data.

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Volume 110, Number 1108   June 2006

Comparison of Experimental and Numerical Investigation on a jet in a Supersonic Cross-Flow

Authors
A. Kovar and E. Schülein

Abstract
Flow interaction of three different jet configurations ejecting air from a flat plate into a supersonic cross flow were investigated experimentally and numerically. The test conditions encompassed a jet pressure ratio of P0j, P¥ = 100 at a Mach number of M¥ = 5 and Reynolds number of about Re¥ = 25 × 106 based on the length of the flat plate. The investigated test cases are: a) single jet; b) four jets positioned in-line in main flow direction; c) four jets positioned side-by-side in spanwise direction. The prediction of the overall flow phenomena as occurring within the interaction area was in fair agreement with the experiments, although quantitatively differences occur that will be discussed in the paper. The results of the comparison are presented and the experimental data are used to validate the applied code.

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Volume 110, Number 1109   July 2006

Ordinal logistic regression analysis of flight task ratings

Authors
R. Bradley and W. M. Maclaren

Abstract
The relationship between a pilot workload rating for a simulated flight task in the proximity of an offshore platform helideck and three experimental factors – wind speed, wind direction and pilot is investigated. The statistical method employed is ordinal logistic regression, which allows the specifying and fitting of regression relationships between ordered categorical response variables and explanatory variables. The response variable in this context is a pilot’s rating of the workload induced by certain flight tasks, measured on an ordered categorical scale 1 to 10. Estimates of the effects of the explanatory variables are given and their practical significance discussed.

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Volume 110, Number 1109   July 2006

Boundary condition effects on the evolution of a train of vortex pairs in still air

Authors
T. Yehoshua and A. Seifert

Abstract
Effects of boundary conditions on the performance of compact oscillatory momentum and vorticity generators, commonly known as ‘synthetic jet’, ejecting a train of vortex-pairs into still air, were studied experimentally. The different boundary conditions altered the near-device entrainment process of the zero-net-mass-flux actuator. The measurements included hot-wire and Particle Image Velocimetry, cavity pressures and temperatures. When the actuator operates in still air, a quasi-2D vortex pair is generated due to the extreme shear at the edges of the fluid slug ejected during the blowing stage of each excitation cycle. The vorticity flux exiting the slot determines the resulting vortex-pair circulation. The threshold slot exit velocity, for the current configuration and operating conditions, determines if the vortices will be sucked into the actuator’s cavity or be released. Once released, the vortex convection speed approximately scales with the peak velocity at the slot exit. However, the normalised convection velocity increases with the slot Reynolds number. When even a very short extension is attached to one ‘lip’ of the actuator exit, the jet is deflected in the direction opposite the extended lip, due to the restriction on the entrainment process. When long, one ‘lip’ extension is attached, such that the vortex pair is ejected parallel to a plate, the coherence of the vortices improve, their phase speed and magnitude decrease. The effects of high-frequency excitation, ejected perpendicular to a wall into still air, were also investigated. It was found that the presence of the plate does not have a measurable effect on the wall normal excitation, indicating that the majority of the entrainment is taking place from the forward 180° of the actuator exit plane. When the slot is inclined to the surface at a shallow angle of 30 degrees, an unsteady wall jet is formed, transferring momentum along the wall. This is a direct result of the symmetry break, altering the relative magnitudes of the vortex pair.

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Volume 110, Number 1109   July 2006

One CFD calculation to end point flight testing

Authors
A. Cenko

Abstract
Any time a new aircraft is introduced into service, or an old aircraft undergoes substantial modifications or needs to be certified to carry and employ new stores, the store separation engineer is faced with a decision about how much effort will be required to provide an airworthiness certification for the aircraft and stores. Generally, there are three approaches that have been used: wind-tunnel testing, computational fluid dynamics (CFD) analyses and flight testing. During the past twenty years there have been considerable advances in all three areas. In particular, there has been a considerable improvement in the speed and validity of CFD results for store separation. The Holy Grail of CFD has long been the reduction/replacement of wind-tunnel testing. This would mean in store separation the ability to go from a CFD calculation to flight testing at the end point. The paper will describe how this was achieved for the F/A-18C/Litening pod program.

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Volume 110, Number 1109   July 2006

System of systems force structure optimisation

Authors
M. S. McCoy

Abstract
A system of systems study plan was developed and a prototype was executed to optimise a recommended military force structure. This methodology defined the optimal force structure, using constrained optimisation to reflect budget limitations and desired mission performance. The force structure included surface and air assets, a command, control, communications, computers, intelligence, surveillance and reconnaissance (C4ISR) architecture, and a recommended logistics infrastructure. A second aspect of the study plan defined the total acquisition strategy, which accounted for: retiring legacy assets, extending the service life of existing assets until new replacements became available, and acquiring new assets for deployment, within the budget allocation. This methodology combined various modeling and simulation techniques to meet three study objectives. First, a non-linear mixed integer programming model maximised performance, subject to cost constraints, cost as an independent variable (CAIV). Second, a dynamic programming model scheduled the transition from the legacy force structure to the future force, defined by the previous modeling technique. Third, a process simulation model simulated performance, over a one-year time period, for 25 areas of responsibility and five missions. This model verified performance estimates generated by the previous models.

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Volume 110, Number 1109   July 2006

Integrating CFD and piloted simulation to quantify ship-helicopter operating limits

Authors
D. M. Roper, I. Owen, G. D. Padfield and S. J. Hodge

Abstract
This paper describes a study which has been concerned with numerical predictions of the airwakes resulting from two simplified ship geometries: the internationally agreed Simple Frigate Shape, SFS1, and its successor, SFS2. Extensive steady-state simulations have been carried out for a wide range of wind conditions using Fluent, a commercially available Computational Fluid Dynamics (CFD) code. The CFD predictions have been partially validated against wind tunnel data produced by the National Research Council of Canada (NRC) and have shown good agreement. The resulting airwake velocity components have been exported from Fluent, interpolated onto suitable grids and attached to the FLIGHTLAB flight-simulation environment as look-up tables; piloted flight trials were then carried out using the Liverpool full-motion simulator. The pilot workload and helicopter control margins resulting from a range of wind-over-deck conditions have been used to develop the Ship-Helicopter Operating Limits (SHOL) for a Lynx-like helicopter and the SFS2. The workload was compared to the pilot’s experiences on a similar aircraft and a Type 23 Frigate and the simulated SHOL compared with SHOLs derived from sea trials. The results are very encouraging and open up further the long awaited prospect of such simulations being used in the future to reduce at-sea trials, and to provide a safe environment for pilot training.

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Volume 110, Number 1110   August 2006

Efficiency parameters for modern commercial aircraft

Authors
R. K. Nangia

Abstract
Currently, there is great emphasis, worldwide, on environmental issues. This will have an impact on civil aircraft design, manufacture and operation. Since the advent of the jet engine and swept wing aircraft, the trends have naturally tended towards greater productivity through increasing speed and payload. The cruise speed of conventional civil aircraft is unlikely to increase beyond current levels. Further increases in productivity are achieved by increasing payloads. This has led towards larger aircraft with the capability for increased ranges. It is shown that designing aircraft for longer ranges increases fuel burn significantly. A series of aircraft operational parameters have been analysed. Selected data and established trends for current and future aircraft are presented. The data has been interpreted into efficiency terms, relating payload, range, fuel consumed and a measure of unit costs. It is shown that ‘value’ (cost) and noise effective efficiencies decrease dramatically with increasing range. Environmental and economic considerations, in the future, may well demand greater efficiency in preference to productivity. One solution for long-range services is to use short-range hops. Another is via air-to-air refuelling. This will be addressed, in more detail, in a future paper.

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Volume 110, Number 1110   August 2006

Civil aircraft design priorities: air quality? climate change? noise?

Authors
P Brooker

Abstract
A variety of related questions is posed. Are the right priorities for future aircraft design being set now? New civil aircraft types could be ‘silent’, i.e. make much less noise than current types. They could be ‘green’, i.e. safeguard the environment. Is silent as important as green? The crucial answer is that future aircraft design should focus on substantial reductions on climate change impact. The air quality targets proposed by the ‘Sustainable Aviation’ initiative appear very ambitious: they should be pursued only to the extent that they do not affect improved fuel efficiency and reduced climate-changing emissions. Good progress has already been made on the aircraft noise targets proposed by the ‘Sustainable Aviation’ initiative, but again they should be pursued only to the extent that they do not affect improved fuel efficiency and reduced climate-changing emissions. The financial case for designing to reduce aircraft noise in order to deliver novel financial benefits, e.g. increase airport flights at night and/or relocate airports, is weak.

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Volume 110, Number 1110   August 2006

Potential of reducing the environmental impact of aviation by using hydrogen Part I: Background, prospects and challenges

Authors
F. Haglind (formerly Svensson), A. Hasselrot and R. Singh

Abstract
The main objective of the paper is to evaluate the potential of reducing the environmental impact of civil subsonic aviation by using hydrogen fuel. The paper is divided into three parts of which this is Part I, where the background, prospects and challenges of introducing an alternative fuel in aviation are outlined. In Part II the aero engine design when using hydrogen is covered, and in Part III the subjects of optimum cruising altitude and airport implications of introducing liquid hydrogen-fuelled aircraft are raised. Looking at the prospect of alternative fuels, synthetic kerosene produced from biomass turns out to be feasible and offers environmental benefits in the short run, whereas hydrogen seems to be the more attractive alternative in the long run. Powering aero engines and aircraft with hydrogen has been done successfully on a number of occasions in the past. Realising this technology change for a fleet of aircraft poses formidable challenges regarding technical development, energy requirement for producing hydrogen, handling, aircraft design and making liquid hydrogen economically compatible with kerosene.

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Volume 110, Number 1110   August 2006

Towards a silent aircraft

Authors
A.P. Dowling and T. Hynes

Abstract
We set a target for a ‘Silent’ aircraft to be imperceptible outside the airfield perimeter in an urban environment, and then address conceptual designs to meet this requirement. Avoiding some traditional aircraft noise sources requires a radical rethink about the configuration. An all-lifting design has many benefits, enabling a closer integration of airframe and engine than the traditional ‘tube and wing’. Low-noise design includes taking advantage of shielding of engine noise by the airframe; low-noise engines with large, low speed jets; an order of magnitude increase in absorption by liners; and operations for low-noise informing the design. Progress to date on the Silent Aircraft Initiative is presented, along with some conceptual aircraft and engine designs. The further work needed to develop these into viable future aircraft is discussed.

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Volume 110, Number 1110   August 2006

Civil aviation and the environment – the next frontier for the aerodynamicist

Authors
J. J. Green

Abstract
In the coming century, the impact of air travel on the environment will become an increasingly powerful influence on aircraft design. Unless the impact per passenger kilometre can be reduced substantially relative to today’s levels, environmental factors will increasingly limit the expansion of air travel and the social benefits that it brings. The three main impacts are noise, air pollution around airports and changes to atmospheric composition and climate as a result of aircraft emissions at altitude. The lecture will review the work done within the Air Travel – Greener by Design programme to assess the technological, design and operational possibilities for reducing these impacts. The main aeronautical disciplines all have something to contribute but it is in aerodynamics that the greatest opportunities appear to lie. If these opportunities are pursued, the aircraft in production in 2050 could be very different from those of 2005. It is for the aerodynamicists, supported by the structures and systems engineers and the materials scientists, to make the case for a radical leap.

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Volume 110, Number 1110   August 2006

Küchemann’s weight model as applied in the first Greener by Design Technology Sub Group Report: a correction, adaptation and commentary

Authors
J E Green

Abstract
In the first report of the Greener by Design Technology Sub Group, the author made an error in deriving modern values for the empirical constants in the weight model, taken from Küchemann, that was used in the study of fuel efficiency of a range of aircraft designs. In this note the error is corrected and the weight model is also extended to take account of the observed variation with range of the ratio of design payload to maximum payload. This leads to the conclusion that the effect of design range on fuel efficiency is substantially greater than suggested in the Greener by Design report. The conclusion, which is in agreement with a correlation by Nangia of existing aircraft data, indicates that a modern aircraft with a design range of 15,000km burns approximately twice as much fuel per passenger-km as one with a design range of 4,000km. This powerfully reinforces the call made in the Greener by Design reports for in-depth studies to be made of the use of medium-range aircraft for long-distance travel.

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Volume 110, Number 1110   August 2006

Greener manufacturing, maintenance and disposal – towards the ACARE targets

Authors
J.J. Lee

Abstract
This paper looks at how the aerospace industry can achieve the ACARE goal of greener manufacturing, maintenance and disposal. It looks further than merely reducing waste and eliminating hazardous materials and processes and suggests that the organisational structure of the industry will play an important role in facilitating a move towards such a goal. Greater co-operation or integration within the industry at all stages of the product life cycle chain is a fundamental requirement as individual companies run a risk of increasing the total environmental burdens if they concentrate solely on reducing their own impacts without considering the effect a change they make may have on other companies. The use of comprehensive environmental supply chain management systems and end of life plans can smooth the implementation of extended product responsibility and accelerate the benefits of greener manufacturing, maintenance and disposal.

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Volume 110, Number 1111   September 2006

Aerofoil profile and sweep optimisaton for a blended wing-body aircraft using a discrete adjoint method

Authors
A. Le Moigne and N. Qin

Abstract
Aerodynamic optimisations of a Blended Wing-Body (BWB) aircraft are presented. A discrete adjoint solver is used to calculate efficiently the gradients, which makes it possible to optimise for a large number of design variables. The optimisations employ either a variable-fidelity method that combines low- and high-fidelity models or a direct Sequential Quadratic Programming (SQP) method. Four Euler optimisations of a BWB aircraft are then presented. The optimisation is allowed to change a series of master sections defining the aircraft geometry as well as the sweep angle on the outer wing for two of the optimisations. Substantial improvements are obtained, not only in the Euler mode but also when the optimised geometries are evaluated using Reynolds-averaged Navier-Stokes solutions. Some interesting features of the optimised wing profiles are discussed.

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Volume 110, Number 1111   September 2006

Circular flight kite tests: converting to standard results

Authors
J. C. Stevenson and K. V. Alexander

Abstract
Kite testing by flying in a horizontal circle, was developed in order to address the inevitable accuracy problems inherent in pre-existing kite measurement techniques. However the raw results from this circular flight method are not directly comparable with traditional kite performance measurements. To enable direct comparisons to be made, modifying equations have been developed to convert the raw circular flight results into the traditional measurements of lift to drag ratio, and lift coefficient. This paper derives the modifying equations, and presents experimental results comparing traditional measurements with both the raw and modified circular flight results. The modifying equations are applied to an example set of results to assess the sensitivity of the test environment parameters. It is concluded that for many cases, the discrepancy between the raw circular flight test results and traditional measurement techniques is small enough to ignore. Alternatively, the modifying equations given in the paper may readily be encoded so that traditional results may be quickly obtained from this novel test method.

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Volume 110, Number 1111   September 2006

Dynamics and control of single-line kites

Authors
G. Sanchez

Abstract
This paper presents a dynamic analysis of a single-line kite with two degrees of freedom. A Lagrangian formulation is used to write convenient equations of motion. The equilibrium states of the system and their stability are studied; eigenvalues and eigenmodes are calculated by using linear theory. The stability in the parametric plane delta - W0 is discussed, where delta defines the bridle geometry and W0 is wind velocity. The system goes through a Hopf bifurcation and periodic branches of solutions appear. The orbits and their stability have been calculated numerically using Floquet theory and wind velocity seems to play an important role in their existence. Finally the kite response against gusts is considered and an open loop control system developed to keep the flight altitude invariant under changing atmospheric conditions. Modifying the bridle's geometry seems to be a convenient way to control a kite's performance.

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Volume 110, Number 1111   September 2006

Impact of solar storms on high altitude long endurance umanned aircraft and airship design and operations

Authors
L. R. Newcome

Abstract
This paper applies existing information on solar storms to unmanned aviation; no new research data is presented. The purpose of this paper is to alert the unmanned aviation community to the potential hazards posed by solar storms, to familiarize it with the effects of solar storms and how to mitigate them, and to encourage research on solar storm effects on high altitude long endurance (HALE) aircraft and airship design and operations. As unmanned aircraft and airships move increasingly into high altitude (50,000+ ft), endurance (24+ hr) roles, they will become vulnerable to the effects of space weather, specifically that of solar storms. Although solar storms are commonly associated with their impact on satellites, they affect the routing and timing of airline flights flying for 6 to 8 hr at 30,000 to 40,000 ft. Operating twice as high and with flight times twice as long (or longer) than those of airliners, HALE aircraft and airships occupy a middle zone of vulnerability, being more so than airliners but less so than satellites. A key difference however is that satellites are designed for space weather, whereas some current HALE vehicles are not. The paper concludes that unmanned HALE aircraft and airships can be one to three orders of magnitude more vulnerable to solar storms than a trans-Pacific airliner.

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Volume 110, Number 1111   September 2006

Longitudinal flight control design with handling quality requirements

Authors
D. Saussie, L. Saydy and O. Akhrif

Abstract
This work presents a method for selecting the gain parameters of a control law for an aircraft’s longitudinal motion. The design incorporates various handling quality requirements involving modal, time- and frequency-domain criteria that were fixed by the aircraft manufacturer. After necessary model order-reductions, the design proceeds in essentially two-steps: Stability Augmentation System (SAS) loop design and Control Augmentation System (CAS) loop design. The approach partly relies on the use of guardian maps to characterize, in each case, the set of gain parameters for which desired handling quality requirements are satisfied. The approach is applied throughout the full flight envelope of a business jet aircraft and yields satisfactory results.

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Volume 110, Number 1111   September 2006

Aerodynamic effectiveness of the flow of exhaust gases in a generic formula one car configuration

Authors
F. L. Parra and K. Kontis

Abstract
The effects of the flow of exhaust gases intentionally orientated on the rear wing element of a generic Formula One car body have been studied. A qualitative analysis of the effectiveness of a cold nitrogen jet on a NACA 0012 type of aerofoil has been conducted. The Reynolds number of the jet was 13,000, based on the jet velocity and diameter, and of the bodywork was 54,000, based on the free stream velocity and bodywork length. The lift coefficient was measured via a three-component strain-gauge force balance at four different ground-to-aerofoil heights (32, 45, 60 and 90mm) and incidence range -20 to +20 degrees. The surface flow patterns were visualized using the oil flow technique and were compared with numerical simulations. Pressure measurements were conducted using pressure tappings. The CFD solver was FLUENT. The RNG k-e model was selected to solve the turbulent flow transport equations. The numerical study also comprised the investigation of the aspiration generated by exhaust gases when these are ejected inside a duct of greater diameter. A parametric investigation relating the relative diameter of exhaust pipe and outer duct and the relative overlap between the sides of the duct and the exhaust pipe was performed.

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Volume 110, Number 1112   October 2006

A method for predicting the rate and effect of approach to the stall of a microlight aeroplace

Authors
G. B. Gratton

Abstract
The stall and immediately post-stall behaviour of a microlight aeroplane are shown to be a function of the deceleration rate prior to the stall; therefore, it is necessary to use a representative deceleration rate when determining the acceptability of stall and post-stall handling qualities. This research has found means by which the range of deceleration rates likely to be seen in a particular type can be estimated, so that flight test programmes can ensure these rates are included, and thus aircraft are confirmed to have acceptable stalling characteristics. Recommendations are made towards the use of this research for all aircraft type, and of further work which might usefully be carried out.

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Volume 110, Number 1112   October 2006

A comparative study of two UCAV type wing planforms - performance and stability considerations

Authors
R. K. Nangia and M. E. Palmer

Abstract
Currently there is a revival of interest in flying wings for military (and civil) use. The military context has arisen from the future ‘stealthy’ high altitude long endurance (HALE) and unmanned combat air vehicles (UCAV) aircraft. Questions on aerodynamics, control and structural efficiency arise. Compared with conventional wing/tail arrangements, flying wings have a special set of very different constraints. These are mentioned. Without a trim surface, the constraints on the wing pitching moment dictate the design camber and twist. Control power requirements can be high because of effectively short moment arms. The camber and twist are strongly dependent on trim stability margins. This aspect needs to be understood in detail when comparing different types of planforms. This paper covers three inter-related aspects – a wing design method, the suitability of solvers used with the method and a comparative study of two, typical UCAV planforms. This is inspired by the need to understand a variety of wings (in the public domain) that are, at first sight, aimed at similar missions. The main emphasis has been on developing and understanding cruise design camber and twist with Cm constraints of stable, neutral and unstable static margins. Spanwise lift and drag loadings have also been presented. Camber design has been via attained thrust methods and a modal approach. It is shown that starting from basic information such as the planform, we are able to predict the anticipated performance with sufficient confidence for comparative assessments of published project data. Further work is proposed in several areas.

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Volume 110, Number 1112   October 2006

Single and multi-objective UAV aerofoil optimisation via hierarchical asynchronous parallel evolutionary algorithm

Authors
L. F. Gonzalez, D. S. Lee, K. Srinivas and K. C. Wong

Abstract
Unmanned aerial vehicle (UAV) design tends to focus on sensors, payload and navigation systems, as these are the most expensive components. One area that is often overlooked in UAV design is airframe and aerodynamic shape optimisation. As for manned aircraft, optimisation is important in order to extend the operational envelope and efficiency of these vehicles. A traditional approach to optimisation is to use gradient-based techniques. These techniques are effective when applied to specific problems and within a specified range. These methods are efficient for finding optimal global solutions if the objective functions and constraints are differentiable. If a broader application of the optimiser is desired, or when the complexity of the problem arises because it is multi-modal, involves approximation, is non-differentiable, or involves multiple objectives and physics, as it is often the case in aerodynamic optimisation, more robust and alternative numerical tools are required. Emerging techniques such as evolutionary algorithms (EAs) have been shown to be robust as they require no derivatives or gradients of the objective function, have the capability of finding globally optimum solutions among many local optima, are easily executed in parallel, and can be adapted to arbitrary solver codes without major modifications. In this paper, the formulation and application of a evolutionary technique for aerofoil shape optimisation is described.

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Volume 110, Number 1112   October 2006

Wing tip vortex control using synthetic jets

Authors
P. Margaris and I. Gursal

Abstract
An experimental investigation was conducted to study the effect of synthetic jet (oscillatory, zero net mass flow jet) blowing near the wing tip, as a means of diffusing the trailing vortex. Velocity measurements were taken, using a Particle Image Velocimetry system, around the tip and in the near wake of a rectangular wing, which was equipped with several blowing slots. The effect of the synthetic jet was compared to that of a continuous jet blowing from the same configurations. The results show that the use of synthetic jet blowing is generally beneficial in diffusing the trailing vortex and comparable to the use of continuous jet. The effect was more pronounced for the highest blowing coefficient used. The driving frequency of the jet did not generally prove to be a significant parameter. Finally, the instantaneous and the phase-locked velocity measurements helped explain the different mechanisms employed by the continuous and synthetic jets in diffusing the trailing vortex.

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Volume 110, Number 1112   October 2006

Technical Note: Thermal buckling of a thin uniform circular disk: a comparison of predictions

Authors
K. A. Seffen

Abstract
The conditions for thermally-induced buckling of an unloaded thin, circular disk are compared from two well-known but unconnected studies: an approximate solution by Freund for a constant thickness disk, which must neglect the free edge condition, and an exact solution by Mansfield but only for a disk whose thickness tapers to zero in a particular manner. It is shown that buckling occurs at slightly higher values compared to a finite element analysis of a constant thickness disk but that the case of variable thickness seems to offer a closer result, which suggests that it better models the boundary layer behaviour near the free edge.

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Volume 110, Number 1112   October 2006

Considerations for UAV design and operation in South African airspace

Authors
L. A. Ingham, T. Jones and A. Maneschijn

Abstract
At present, the lack of UAV regulations and standards precludes UAVs from being certified to operate commercially in un-segregated civilian airspace. Because of strategic, economical and security requirements, it is necessary to devise a method to operate UAVs in South African airspace within existing regulatory arrangements. This paper suggests specific UAV missions, viz.; maritime patrol/boarder control, search & rescue, and cargo transport, together with design considerations and possible concepts of UAV; operations, maintenance and training, that will enable UAVs to satisfy the immediate South African strategic requirements whilst further UAV standards and regulations are being developed.

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Volume 110, Number 1113   November 2006

Operations and aircraft design towards greener civil aviation using air-to-air refuelling

Authors
R. K. Nangia

Abstract
As civil aviation expands, environmental aspects and fuel savings are becoming increasingly important. Amongst technologies proposed for more efficient flight, air-to-air refuelling (AAR), ‘hopping’ and flying in close formation (drag reduction), all have significant possibilities. It will be interesting to know also how these technologies may co-exist e.g. AAR and formation flying. In military use, AAR is virtually indispensable. Its benefits are real and largely proven in hostile and demanding scenarios. We present a case for applying AAR in a civil context to show that substantial reductions in fuel burn for long-range missions are achievable. Overall savings, including the fuel used during the tanker missions, would be of the order of 30-40% fuel and 35-40% financial. These are very significant in terms of the impact on aviation’s contribution to reducing atmospheric pollution. AAR allows smaller, efficient (greener) aircraft optimised for about 3,000nm range to fulfil long-range route requirements. This implies greater usage of smaller airports, relieving congestion and ATC demands on Hub airports. Problems due to shed vortices and wakes at airports are reduced. Smaller engines will be needed. Integrated (accepted) AAR could lead to further benefits. Aircraft could take-off ‘light’, with minimum fuel and reserves and a planned AAR a few minutes into the flight. The ‘light’ aircraft would not require over-rating of the engines during take-off and would therefore be less noisy during take-off and climb-out, permitting more acceptable night operations.

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Volume 110, Number 1113   November 2006

Research initiatives for improving the safety of offshore helicopter operations

Authors
D. A. Howson

Abstract
Since the late 1980’s, the UK Civil Aviation Authority (CAA) has been leading a programme of research aimed at improving the safety of offshore helicopter operations. The motivation for this initiative came from a major joint CAA/Industry review of helicopter airworthiness, commissioned in 1982. This study led to a number of research projects and other reviews which, in turn, led to further research projects. A total of over 20 projects have been undertaken covering airworthiness and operational issues, and covering helicopters and helidecks. This programme of work has been jointly funded and monitored by the UK CAA-run Helicopter Safety Research Management Committee (HSRMC). This paper provides a top-level summary of current activities on the seven main ‘live’ research projects

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Volume 110, Number 1113   November 2006

Further analysis of self-induced roll oscillations of a non-slender delta wing

Authors
M. E. Beyers and L. E. Ericsson

Abstract
In low-speed wind tunnel tests at alphaƒn= 25 and 30 deg of a 45 deg delta wing with semicircular leading edges limit cycle oscillations occurred around the 50 deg roll trim angle. In some cases the oscillations were highly regular, in other cases, highly irregular. An analysis of the observed roll-oscillation dynamics has shown that several viscous flow phenomena are involved, which depend strongly on the leading-edge geometry, and whose relative importance can vary dramatically with the existing Reynolds number in critical flow regions. The possible role of surface roughness in modifying the viscous flow/motion coupling to cause these dramatically different test results is examined.

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Volume 110, Number 1113   November 2006

Integration of friction stir welding into a multidisciplinary aerospace design framework

Authors
A. H. van der Laan, R. Curran, M. J. L. van Tooren and C. Ritchie

Abstract
Multidisciplinary design and innovative highly automated manufacturing methods are increasingly important to today’s aircraft industry: multidisciplinary design because it reduces lead-time and results in a better design, and automated manufacturing methods because they are more capable and reduce manufacturing cost. In this paper a cost estimation model is presented that integrates the manufacturing cost of friction stir welded connections within a multidisciplinary design decision tool. Due to the fact that friction stir welding is a new manufacturing method, the cost estimation model is based on the actual process physics, meaning what the process looks like in terms of processing speeds and characteristics. As an integral part of a multidisciplinary design framework, the developed cost estimation model contributes to a design support tool that assesses not only manufacturing but also structural and aerodynamic issues. It is shown that the cost model developed can be integrated into this more holistic design process support architecture. The predicted costs are accurate to the historical data and allow tradeoff of manufacturing and economic considerations within the context of the multidisciplinary design tool. The tradeoff capability is highlighted through a presented case study that compares the friction stir welding process as an alternative solution to more tradition riveting. Most importantly, this results in a quantitative tradeoff between two processes that shows the manufacturing cycle time of friction stir welding to be reduced by 60% and the recurring assembly cost by 20%.

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Volume 110, Number 1113   November 2006

Pressure sensitive paint measurements on a delta-wing in supersonic flow

Authors
L. C. Raju, L. Venkatakrishnan and P. R. Viswanath

Abstract
Experiments have been performed documenting the pressure field on the lee-side of a delta-wing at three incidence angles (5°, 10°, and 15°) and at Mach 1•8 using a PSP (Pressure Sensitive Paint) technique. The delta-wing model having a leading edge sweep of 60° was instrumented with 31 spanwise pressure ports at 68% of mean chord location. The Optrod-B1 binary paint was utilised and the PSP images were processed employing a resection based methodology. The comparisons of PSP results with those measured employing pressure taps show good agreement at different incidence angles.

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Volume 110, Number 1113   November 2006

A turbulence criterion for safe helicopter operations to offshore installations

Authors
S. J. Rowe, D. Howson and G. Turner

Abstract
This paper describes the development of a wind turbulence criterion for the safe operation of helicopters to offshore installations. The development of the criterion was recommended following a review of the environmental effects around offshore platform helidecks. Currently, criteria exist for ambient temperature and for vertical wind component in the vicinity of helidecks, but a questionnaire-based survey of helicopter pilots revealed that the principal safety hazard and source of highest workload is turbulence around offshore installations. The new turbulence criterion will plug a long-standing gap in the guidance on offshore helideck design. The paper describes how the criterion has been developed using piloted flight simulation in a research flight simulator together with data from wind tunnel tests on offshore platforms. Initial validation has been successfully performed, and extended to include correlation with the large database of helicopter operational flight data records being collected through the UK North Sea Helicopter Operations Monitoring Programme (HOMP). The turbulence criterion will be used, together with existing criteria on vertical wind component and temperature, in the assessment of new offshore installation designs, or proposed modifications to existing designs, to determine wind conditions where turbulence is likely to be excessive for safe helicopter operations. These will be used to estimate helideck operability and thereby inform the installation topsides design process, and will provide input to the setting and maintenance of helicopter operational limitations for individual installations.

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Volume 110, Number 1114   December 2006

3D numerical simulation of the supersonic combustion of H2

Authors
Prashant Dinde, A. Rajasekaren and V. Babu

Abstract
Results from numerical simulations of supersonic combustion of H2 are presented. The combustor has a single stage fuel injection parallel to the main flow from the base of a wedge. The simulations have been performed using FLUENT. Realisable k-e model has been used for modelling turbulence and single step finite rate chemistry has been used for modelling the H2-Air kinetics. All the numerical solutions have been obtained on grids with average value for wall y+ less than 40. Numerically predicted profiles of static pressure, axial velocity, turbulent kinetic energy and static temperature for both non-reacting as well as reacting flows are compared with the experimental data. The RANS calculations are able to predict the mean and fluctuating quantities reasonably well in most regions of the flow field. However, the single step kinetics predicts heat release much more rapid than what was seen in the experiments. Nonetheless, the overall pressure rise in the combustor due to combustion is predicted well. Also, the k-e model is not able to predict the fluctuating quantities in the base region of the wedge where there is strong anisotropy in the presence of combustion.

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Volume 110, Number 1114   December 2006

Using system engineering on an aircraft improvement project

Authors
J. C. Hsu

Abstract
A complete system engineering process is applied to a pilot project that will determine the initial deployment of the system engineering process for future projects. It was a challenge to complete the entire systems engineering process to include project team utilization of system engineering tools in such a short time span. Therefore, systems engineering products had to be useful and productive to the project. The system requirements definition, Quality Function Deployment (QFD) evaluation, trade study, risk identification and risk mitigation processes were completed in a timely manner and assisted in the System Requirements, System Design and Preliminary Design Reviews successfully.

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Volume 110, Number 1114   December 2006

Decoupled controller for mixed exhausts turbofan engine

Authors
T. R. Nada

Abstract
This paper points out the capabilities of fully decoupled fuzzy controller which introduces simple design approach to deal with the coupling effects in controlling two spools, mixed exhausts turbofan engines. The decoupling is performed through proper selection of input parameters to the controller. Digital nonlinear engine/control system simulation is used to construct the fuzzy rules depending on simple logic. The performance of this controller is compared with that of an optimal controller representing efficient classical and conventional techniques. The decoupled fuzzy control system produces favorable transient strategies that other conventional controllers can not attempt due to its inherent proportionality characteristics. It displays improvements in surge margin for both fan and compressor, and temperature margin with almost similar response time during acceleration. Also, the proposed controller has the capabilities to increase the response speed during deceleration independently from acceleration transient.

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Volume 110, Number 1114   December 2006

Aeroelastic response of helicopter rotors using a 3D unsteady aerodynamic solver

Authors
M. Gennaretti and G. Bernardini

Abstract
The prediction of blade deflections and vibratory hub loads concerning helicopter main rotors in forward flight is the objective of this work. They are determined by using an aeroelastic model derived through the coupling between a nonlinear blade structural model and a boundary integral equation solver for three-dimensional, unsteady, potential aerodynamics. The Galerkin method is used for the spatial integration, whereas the periodic blade response is determined by a harmonic balance approach. This aeroelastic model yields a unified approach for aeroelastic response and blade pressure prediction that may be used for aeroacoustic purposes, with the possibility of including effects from both blade-vortex interaction and multiple-body aerodynamic interaction. Quasi-steady aerodynamic models with wake-inflow from the three-dimensional aerodynamic solver are also applied, in order to perform a comparative study. Numerical results show the capability of the aeroelastic tool to evaluate blade response and vibratory hub loads for a helicopter main rotor in level flight conditions, and examine the sensitivity of the predictions on the aerodynamics model used.

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Volume 110, Number 1114   December 2006

Considerations for flight testing of UAVs in South African airspace

Authors
L. A. Ingham, T. Jones and A. Maneschijn

Abstract
South Africa has strategic requirements for tasks such as maritime patrol and border control. Research on UAVs should be done in order to design, certify and operate UAVs in civil airspace to satisfy these requirements. If principles such as equivalence, initially proposed by Eurocontrol are to be adopted in South Africa, it then follows that similar standards used by manned aircraft should be used by UAVs. Similarly, because the process of creating UAV regulations has not kept up with the pace of UAV development, and because dedicated UAV regulations do not yet exist in South Africa, UAVs must be tested and evaluated in order to prove compliance with comparable manned aircraft regulations in the foreseeable future until regulations are created or modified to accommodate UAVs. Given the airspace restrictions, and lack of applicable standards and regulations, proper flight testing of UAVs can become a very specialized task. Most test techniques applied to testing of manned aircraft are fortunately equally applicable to UAVs. This is a research-based paper that provides guidance to flight testers, UAV developers and research organizations wishing to execute tests in South Africa by suggesting a number of considerations for testing of UAVs.

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Volume 110, Number 1114   December 2006

Waypoint navigation for a micro air vehicle using vision-based attitude estimation

Authors
J. J. Kehoe, R. S. Causey, M. Abdulrahim and R. Lind

Abstract
Missions envisioned for micro air vehicles may require a high degree of autonomy to operate in unknown environments. As such, vision is a critical technology for mission capability. This paper discusses an autopilot that uses vision coupled with GPS and altitude sensors for waypoint navigation. The vision processing analyses a horizon to estimate roll and pitch information. The GPS and altitude sensors then command values to roll and pitch for navigation between waypoints. A flight test of a MAV using this autopilot demonstrates the resulting closed-loop system is able to autonomously reach several waypoints. The vehicle actually uses a telemetry link to a ground station on which all vision processing and related guidance and control is performed. Several issues, such as estimating heading to account for slow updates, are investigated to increase performance.

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Volume 111, Number 1115   January 2007

Optical imaging techniques for hypersonic impulse facilities

Authors
T. J. McIntyre, H. Kleine and A. F. P. Houwing

Abstract
The application of optical imaging techniques to hypersonic facilities is discussed and examples of experimental measurements are provided. Traditional schlieren and shadowgraph techniques still remain as inexpensive and easy to use flow visualisation techniques. With the advent of faster cameras, these methods are becoming increasingly important for time-resolved high-speed imaging. Interferometry’s quantitative nature is regularly used to obtain density information about hypersonic flows. Recent developments have seen an extension of the types of flows that can be imaged and the measurement of other flow parameters such as ionisation level. Planar laser induced fluorescence has been used to visualise complex flows and to measure such quantities as temperature and velocity. Future directions for optical imaging are discussed.

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Volume 111, Number 1115   January 2007

Computation and experimental investigations for low-Reynolds number flows past and aerofoil

Authors
W. Yuan, M. Khalid, J. Windte, U. Scholz and R. Radespiel

Abstract
This paper presents investigations of low-Reynolds-number flows past an SD7003 airfoil at Re = 60k, where transition takes place across a laminar separation bubble (LSB). Results of experimental measurements and numerical calculations are analyzed and discussed. In particular, reasonably good results were obtained using two different numerical approaches: Large-eddy simulation (LES) that demonstrated vortical structures at different transition stages, and where the transition occurred naturally; unsteady Reynolds-averaged Navier-Stokes (URANS) simulations for several turbulence models based on the w-length-scale equation, coupled to a linear stability solver to predict the transition position.

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Volume 111, Number 1115   January 2007

Effect of stagnation temperature on supersonic flow parameters applicatio for air in nozzles

Authors
T. Zebbiche and Z. Youbi

Abstract
When the stagnation temperature of a perfect gas increases, the specific heats and their ratio do not remain constant and start to vary with the temperature. The gas remains perfect; its state equations remain valid, so it can be named as calorifically imperfect gas. The aim of this research is to develop the necessary thermodynamic and geometrical equations and to study the supersonic flow at high temperature, lower than the dissociation threshold. The results are found by the resolution of nonlinear algebraic equations and integration of complex analytical functions where the exact calculation is impossible. The dichotomy method is used to solve the nonlinear equations and Simpson’s algorithm for the numerical integration applied. A condensation of the nodes is used. The functions to be integrated have a high gradient at the extremity of the interval of integration. The comparison is made with the calorifically perfect gas to determine the error. The application is made for air in a supersonic nozzle.

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Volume 111, Number 1115   January 2007

Aircraft flight characteristics in conditions of windshear and icing

Authors
Yihua Cao and Kungang Yuan

Abstract
Complex weather conditions, especially windshear and icing encounter, have severe effects on aircraft flight safety. The effect of low-altitude windshear and ice accretion on aircraft performance and control has been studied in this paper. With the employment of a windshear model and nonlinear inverse dynamics (NID) method, a low-altitude windshear penetration flight control law is designed. The effect of ice accretion was modeled on the stability and control of an aircraft. Several icing parameters are imported to the small disturbance flight dynamics model to calculate the change of performance, stability and control derivatives between clean and iced aircraft. These derivatives were used to calculate the elevator, the aileron and the rudder step responses to investigate the icing effect. The simulation results indicate that the NID control logic works effectively in the trajectory control of the aircraft during the penetration of windshear. The method used to study the effect of ice accretion on aircraft is valid and it can provide data for real-time calculation for icing encounter.

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Volume 111, Number 1115   January 2007

Numerical exploration of starting process in supersonic nozzle

Authors
S. Saha and D. Chakraborty

Abstract
The starting process in a supersonic nozzle is numerically simulated. The Navier Stokes equations, in axisymmetric form, are solved using a higher order spatial and temporal accurate scheme. Good comparisons between experimental and numerical values of various flow parameters form the basis of further analysis. The insight of the starting process in the nozzle, namely, the movement of primary and secondary shocks and contact discontinuity, has been obtained through analysis of various flow parameters. It has been observed that the inviscid phenomenon is more predominant in the flow development process. Parametric studies have been carried out to determine the effect of nozzle divergence angle on the starting process.

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Volume 111, Number 1116   February 2007

New commercial opportunities in space

Authors
D. M. Ashford

Abstract
This paper assesses new commercial opportunities in space. The main conclusion is that spaceplanes can reduce the cost of human transport to orbit sufficiently for large new commercial markets to develop. Combining the reusability of spaceplanes with the high traffic levels of space tourism offers the prospect of a thousandfold reduction in the cost per seat to orbit. The result will be airline operations to orbit involving dozens of spaceplanes, each capable of one or two flights per day. These low costs will make possible a rapid expansion of space science and exploration. The prototype of a small orbital spaceplane, needed to trigger this line of development, could be developed in about six years at a cost comparable to one or two flights of the Space Shuttle. It might be possible to progress from this prototype to airline operations within ten years, given a massive development effort.

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Volume 111, Number 1116   February 2007

Rotorcraft simulation modelling and validation for control law design

Authors
B. J. Manimala, D. J. Walker, G. D. Padfield, M. Voskuijl and A. W. Gubbels

Abstract
This paper describes the development and validation of a high fidelity simulation model of the Bell 412 helicopter for handling qualities and flight control investigations. The base-line model features a rigid, articulated blade-element formulation of the main rotor, with flap and lag degrees of freedom. The Bell 412 HP engine/governor dynamics are represented by a second-order system. Other key features of the base–line model include a finite-state dynamic inflow model and lag damper dynamics. The base-line model gives excellent agreement with flight-test data over the speed range 15-120kt for on-axis responses. Prediction of off-axis responses is less accurate. Several model enhancement options were introduced to obtain an improved off-axis response. It is shown that the pitch/roll off-axis responses in transient manoeuvres can be improved significantly by including wake geometry distortion effects in the Peters-He finite-state dynamic inflow model.

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Volume 111, Number 1116   February 2007

Performance of non-rigid airships operating in the neutral buoyancy condition

Authors
G. E. Dorrington

Abstract
The feasibility of using neutrally-buoyant (or fully-buoyant) airships for passenger and cargo transportation is investigated. The drag coefficients of rigid and non-rigid airships are deduced from flight data. Comparisons are made with empirical drag formulas and previous wind tunnel data. Some general trends for airship drag are derived. The mass breakdown of non-rigid airships with hull volumes up to 35,000m3 is analysed using parametric equations. The maximum feasible airspeed and useful load carrying capacity of projected airships are calculated. ‘Specific productivity’ is found to be lower than values achievable with fixed-wing aircraft, but ‘fuelspecific productivity’ is found to be competitive, confirming results of a previous NASA study. The use of gaseous hydrogen and fuel cells is briefly discussed.

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Volume 111, Number 1116   February 2007

Lean engineering: a framework for doing the right thing right

Authors
H. L. McManus, A. Haggerty and E. Murman

Abstract
Lean techniques are having a major impact on aerospace manufacturing. However, the cost and value of aerospace (and many other) products is determined primarily in product development. Migrating lean to engineering processes is ongoing in the industry, and a subject of study at the MIT Lean Aerospace Initiative. This paper summarises findings to date, with references to both research literature and successful implementation examples. To implement lean engineering, a three-part approach is needed: Creating the right products, with effective lifecycle and enterprise integration, using efficient engineering processes.

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Volume 111, Number 1116   February 2007

Design and performance of thin, circular arc, wind-tunnel turning vanes

Authors
G. Johl, M. Passmore and P. Render

Abstract
Although test rig data exists for ¼ circle turning vanes, the actual performance of these vanes once installed in a wind tunnel, and the extent to which test rig results are replicated, is rarely known. This paper compares pressure loss coefficient and velocity profile data from a vane test module with measurements taken in the low speed wind tunnel described in Ref. 1. The pressure loss coefficient, KL is defined as the ratio between the static pressure loss in a corner and the inlet dynamic pressure. Previous investigations in test rigs have shown that thin ¼ circle turning vanes with a space to chord ratio (s/c) of between 0×20-0×25, produced 0×12 < KL < 0×20(2)(3)(4)(5). However, these sources focused on determining KL rather than quantifying the flow quality downstream of the vanes. Although KL, is important in terms of achieving a high tunnel energy ratio, it is perhaps secondary to downstream flow quality since the stream exiting the corners of a typical wind tunnel enter into components whose performance may be affected by flow quality.

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Volume 111, Number 1117   March 2007

High performance computing and computational aerodynamics in the UK

Authors
D. R. Emerson, A. J. Sunderland, M. Ashworth and K. J. Badcock

Abstract
The establishment of the UK Applied Aerodynamics Consortium in 2004 brought together many of the UK’s leading research groups to tackle challenging aerodynamic problems on the national computing facility, HPCx. This paper provides a brief history of some early pioneers of numerical simulation and highlights some key contributions to development in parallel processing that laid the foundations for today’s researchers. The transition from vector to massively parallel processing is discussed from a UK viewpoint along with technological barriers that could have a significant impact on future systems. Solutions to these barriers are already being sought and the paper discussed some of the novel technologies that may be deployed in the future. In its short history, the consortium has made substantial progress and this is briefly discussed with several highlights that illustrate the scientific output. Although a number of challenges are identified, particularly with respect to developing a comprehensive visualisation capability, the consortium is well placed to build upon its initial success.

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Volume 111, Number 1117   March 2007

Numerical study of transonic covity flows usinf large-eddy and detached-eddy simulation

Authors
P. Nayyer, G. N. Barakos and K. J. Badcock

Abstract
Numerical analysis of the flow in weapon bays modelled as open rectangular cavities of length-to-depth (L/D) ratio of 5 and width-to-depth (W/D) ratio of 1 with doors-on and doors-off is presented. Flow conditions correspond to Mach and Reynolds numbers (based on cavity length) of 0×85 and 6×783m respectively. Results from unsteady Reynolds-averaged Navier-Stokes (URANS), large-eddy simulation (LES) and detached-eddy simulation (DES) are compared with the simulation methods demonstrating the best prediction of this complex flow. It was found that URANS was not able to predict the change of flow characteristics between the doors-on and doors-off configurations. In addition, the energy content of the cavity flow modes was much better resolved with DES and LES. Further, the DES was found to be quite capable for this problem giving accurate results (within 3dB of) experiments and appears to be a promising alternative to LES for modelling massively separated flows.

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Volume 111, Number 1117   March 2007

Parallel adjoint-based optimisation of a blended wing body aircraft with shock control bumps

Authors
W. S. Wong, A. Le moigne and N. Qin

Abstract
An Euler optimisation for a BWB configuration with winglets incorporating an array of three-dimensional shock control bumps is carried out by employing an efficient adjoint-based optimisation methodology. A high fidelity multi-block grid with over two million grid points is generated to resolve the shape of the 3D shock control bumps, the winglet as well as the overall BWB shape, which are parameterised by over 650 design variables. In order to perform such a large aerodynamic optimisation problem feasibly, the optimisation tools such as the flow solver and the adjoint solver have to be parallelised with a good parallel efficiency. This paper reports the parallel implementation efforts on the adjoint solver; especially on the calculation of the sensitivity derivatives, which has to be looped over the total number of design variables. Results from the optimisation of the wing master sections, winglet aerofoil sections and the three dimensional bumps indicate a significant improvement regarding the aerodynamic performance against the baseline geometry for the given planform layout of the aircraft.

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Volume 111, Number 1117   March 2007

Prediction of aerodynamic forces on a helicopter fuselage

Authors
A. Filippone

Abstract
This paper presents a critical analysis of the aerodynamic loads created by the airframe of a conventional helicopter. The airframe is modelled and computed with an implicit, multi-block, multi-grid parallel Navier-Stokes solver. The flow solver has been optimised and run on up to 200 parallel processors. The cases reported include the effects of angle-of-attack (positive and negative), the effects of yaw (starboard and port) and side flow. Finally, the effects of the support strut in the wind tunnel experiments have been evaluated. Data are shown for the lift, drag and side force coefficients at flight Reynolds numbers (Re = 30m). A case of 30 degrees yaw at a flight Reynolds number is shown. We conclude that with the use of top-end computer resources it is possible to calculate the aerodynamic coefficients with a good degree of accuracy if the flow is mostly attached.

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Volume 111, Number 1117   March 2007

Achieving high parallel performance for an unstructured unsteady turbomachinery CFD code

Authors
N. Hills

Abstract
This paper describes the work done to achieve high parallel performance for an unstructured, unsteady turbomachinery computational fluid dynamics (CFD) code. The aim of the work described here is to be able to scale problems to the thousands of processors that current and future machine architectures will provide. The CFD code is in design use in industry and is also used as a research tool at a number of universities. High parallel scalability has been achieved for a range of turbomachinery test cases, from steady-state hexahedral mesh cases to fully unsteady unstructured mesh cases. This has been achieved by a combination of code modification and consideration of the parallel partitioning strategy and resulting load balancing. A sliding plane option is necessary to run fully unsteady multistage turbomachinery test cases and this has been implemented within the CFD code. Sample CFD calculations of a full turbine including parts of the internal air system are presented.

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Volume 111, Number 1117   March 2007

Large-eddy simulation of twin impinging jets in cross-flow

Authors
Q. Li, G. J. Page and J. J. McGuirk

Abstract
The flow-field beneath a jet-borne vertical landing aircraft is highly complex and unsteady. large-eddy simulation is a suitable tool to predict both the mean flow and unsteady fluctuations. This work aims to evaluate the suitability of LES by applying it to two multiple jet impingement problems: the first is a simple twin impinging jet in cross-flow, while the second includes a circular intake. The numerical method uses a compressible solver on a mixed element unstructured mesh. The smoothing terms in the spatial flux are kept small by the use of a monitor function sensitive to vorticity and divergence. The WALE subgrid scale model is utilised. The simpler jet impingement case shows good agreement with experiment for mean velocity and normal stresses. Analysis of time histories in the jet shear layer and near impingement gives a dominant frequency at a Strouhal number of 0×1, somewhat lower than normally observed in free jets. The jet impingement case with an intake also gives good agreement with experimental velocity measurements, although the expansion of the grid ahead of the jets does reduce the accuracy in this region. Turbulent eddies are observed entering the intake with significant swirl. This is in qualitative agreement with experimental visualisation. The results show that LES could be a suitable tool when applied to multiple jet impingement with realistic aircraft geometry.

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Volume 111, Number 1117   March 2007

Application of a parallel rotor CFD code on HPCx

Authors
C. B. Allen, A. G. Sunderland and R. Johnstone

Abstract
Aspects of parallel simulation of rotor flows are considered. These flows can be extremely expensive for a compressible finite-volume CFD code, and parallelisation can be essential. The award of HPCx time through the UK Applied Aerodynamics Consortium has allowed large rotor simulations to be performed and wake grid dependence to be investigated. However, there are several issues that need to be investigated when considering very large simulations, including the grid generation process, the parallel flow-solver, including an effective mesh motion approach, and visualisation options. Details of these are presented here, with particular emphasis on the flow-solver parallel performance. A detailed performance analysis of the unsteady flow-solver has been undertaken and the code optimised to improve parallel performance, and details of the parallel scaling performance are presented. The parallel scaling of the code is very good on all the HPC architectures tested here, and this has been recognised by an HPCx Gold Star Capability Incentive award. Results of simulation of a four-bladed lifting rotor in forward flight are also presented, for two mesh densities. It is shown that the solution computed on the serial limit on mesh size, around four million cells, exhibits excessive diffusion, and is of limited use in terms of detailed flow features. The results on a very fine mesh, 32 million cells, have shown a much better solution resolution, and it is also demonstrated that the l2 vortex core visualisation option is extremely useful.

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Volume 111, Number 1117   March 2007

An unsteady, moving mesh CFD simulation for Harrier hot-gas ingestion control analysis

Authors
G. A. Richardson, W. N. Dawes and A. M. Savill

Abstract
Hot gas ingestion (HGI) can be a problematic feature of short take-off vertical landing (STOVL) aircraft during the descent phase of landing, or while on the ground. The hot exhaust gases from the downwards pointing nozzles can be re-ingested into the engine intakes, causing power degradation or reduced engine surge margin. The flow-fields that characterise this phenomenon are complex, with supersonic impinging jets and cross-flows creating large ground vortices and fountain up-wash flows. A flow solver has been developed to include a suitable linear mesh deformation technique for the descending aircraft configuration. The code has been applied to predict the occurrence of HGI, by simulating experimental results from a 1/15th scale model of a descending Harrier. This has enabled an understanding of the aerodynamic mechanisms that govern HGI, in terms of the near-field and far-field effects and their impact on the magnitude of temperatures at the engine intake. This paper presents three sets of CFD results. First a validation exercise shows predicted results from the twin-jet with intake in cross-flow test-case. This is an unsteady Reynolds averaged Navier Stokes (URANS) solution for a static geometry (there is no moving mesh). This allows comparison with experiment. Secondly, a full descent phase URANS Spalart-Allmaras (SA) turbulence model calculation is done on an 8×5m cell mesh for half the flow domain of the Harrier model and test-rig without dams/strakes. This shows how the HGI flow mechanisms affect the engine intake temperature profiles, for the case where there are no flow control methods on the underside of the aircraft. Thirdly, the full descent phase URANS SA turbulence model calculation is done on a 22×4m cell mesh for the full flow domain of the Harrier model and test-rig, with the dam/strake geometry included in the structured mesh region.

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Volume 111, Number 1118   April 2007

Analysis of composite plates with variable stiffness using Galerkin method

Authors
E Sencocak and H Tanriover

Abstract
A solution methodology is developed to solve plane stress problem of composite plates with variable stiffness by using Galerkin technique and polynomials as trial functions. In the solution process, analytical computation has been done wherever it is possible, and analytical-numerical type approach has been made for all problems. The methodology is applied to two known case problems, composite plate with variable fibre content and laminated plate with spatially varying fibre orientations. The formulation of these problems results into coupled partial differential equations (with variable coefficients). The solutions of these equations are obtained using the polynomials as trial functions in the Galerkin method. The results are compared to that of Ritz and collocation technique published elsewhere. The method is found to determine closely both the displacements and the stresses with a few number of terms and in good agreement with other approximating methods. Computations on some examples show that, the method with the help of a symbolic math package is simple and efficient for solving these types of problems in engineering applications.

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Volume 111, Number 1118   April 2007

The Mil-Std-1553B data bus: What does the Future hold?

Authors
D R Bracknell

Abstract
Numerous military platforms (land, sea and air) feature serial data bus technology based on the US MIL-STD-1553B data bus standard for integration of their digital systems. Many of these platforms have 15-20 years of operational life remaining, but the installed 1553B data buses (data networks) having only a 1Mbit/sec transfer rate are unable to meet many of the future data networking requirements. Research into new, higher performance data networks has concentrated on modern alternatives with throughput increases of two to three orders of magnitude (100Mbit/sec to 1Gbit/sec). These are generally based on modern commercial-off-the-shelf (COTS) standards, good examples being Ethernet and Fibre Channel. Some are already being employed in military platforms having been ruggedised for the harsh physical and electro-magnetic environment. However these COTS systems while being a natural choice for new platforms may not be cost effective for upgrading older platforms. This paper plots the history of MIL-STD-1553, possibly the most successful military platform standard of all time, and discusses some of the options for increasing its performance and economically extending its life into the future.

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Volume 111, Number 1118   April 2007

Development of a parametric-based indirect aircraft structural usage monitoring system using artificial neural networks

Authors
S C Reed

Abstract
The development of a parametric-based indirect aircraft structural usage monitoring system using artificial neural networks is described. Flight parametric data, captured during Operational Loads Measurement have been used to predict strains or stresses at key structural locations for several military aircraft types, using mapping relationships determined by artificial neural networks. A framework for the development of a neural network-based structural usage monitor is discussed and the basic architecture of the multilayer perceptron artificial neural network is described. Additionally, results from case studies are presented. It is concluded that this technology could provide the basis for accurate, cost-effective structural usage monitoring systems across the range of military aircraft types and roles.

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Volume 111, Number 1118   April 2007

Development of extended ultra high lift low pressure turbine blades using selective roughness and wake unsteadiness

Authors
R Howell and K M Roman

Abstract
This paper describes how it is possible to reduce the profile losses on ultra high lift low pressure (LP) turbine blade profiles with the application of selected surface roughness and wake unsteadiness. Over the past several years, an understanding of wake interactions with the suction surface boundary layer on LP turbines has allowed the design of blades with ever increasing levels of lift. Under steady flow conditions, ultra high lift profiles would have large (and possibly open) separation bubbles present on the suction side which result from the very high diffusion levels. The separation bubble losses produced by it are reduced when unsteady wake flows are present. However, LP turbine blades have now reached a level of loading and diffusion where profile losses can no longer be controlled by wake unsteadiness alone. The ultra high lift profiles investigated here were created by attaching a flap to the trailing edge of another blade in a linear cascade — the so called flap-test technique. The experimental set-up used in this investigation allows for the simulation of upstream wakes by using a moving bar system. Hotwire and hotfilm measurements were used to obtain information about the boundary-layer state on the suction surface of the blade as it evolved in time. Measurements were taken at a Reynolds numbers ranging between 100,000 and 210,000. Two types of ultra high lift profile were investigated; ultra high lift and extended ultra high lift, where the latter has 25% greater back surface diffusion as well as a 12% increase in lift compared to the former. Results revealed that distributed roughness reduced the size of the separation bubble with steady flow. When wakes were present, the distributed roughness amplified disturbances in the boundary layer allowing for more rapid wake induced transition to take place, which tended to eliminate the separation bubble under the wake. The extended ultra high lift profile generated only slightly higher losses than the original ultra high lift profile, but more importantly it generated 12% greater lift.

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Volume 111, Number 1118   April 2007

A systems approach to training aeronautical decision making: from identifying training needs to verifying training solutions

Authors
W.-C. Li and D. Harris

Abstract
The human factors analysis and classification system (HFACS) was developed as an analytical framework for the investigation of the role of human error in aviation accidents. A total of 523 accidents in the Republic of China (ROC) Air Force between 1978 and 2002 were analysed using this framework. The results showed that in a great many cases, poor pilot decision making was implicated. Following a survey of flight instructors’ opinions, two of most promising mnemonic-based methods currently available to guide the decision making of pilots were identified (SHOR and DESIDE). These methods were developed into a short (four hour) aeronautical decision making training course. A total of 41 pilots from the Republic of China Tactical Training Wing then participated in a study to evaluate the effectiveness of this training course. Half of the participants received the short ADM training programme and half did not. Their decision making skill was evaluated in a series of emergency situations presented in a full-flight simulator. Furthermore, their decision making processes were examined in a series of pencil-and-paper based tests. The results clearly showed significant improvements in the quality of pilots’ situation assessment and risk management (underpinning processes in pilot decision making) although this was usually at the expense of speed of response. Pilots used the quicker to apply SHOR mnemonic in situations that which required a fast decision and the more comprehensive but slower to perform DESIDE method when there were fewer time pressures. The results do strongly suggest that ADM is trainable and the short programme devised was effective.

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Volume 111, Number 1118   April 2007

Relationships between flying qualities and flight tests parameters for the F/A-18 aircraft

Authors
R. M. Botez and M. Rotaru

Abstract
In this Technical Note, is shown that relationships exist between flying qualities levels 1, 2 and 3 and flight conditions expressed in terms of Mach numbers, altitudes and angles-of-attack for the F/A-18 SRA (System Research Aircraft). These relationships are helpful in detecting if derivatives are well calculated for flight tests intermediate conditions. The stability and control derivatives were calculated at NASA Dryden Flight Research Center DFRC laboratories for a number of 52 flight test conditions for the longitudinal and lateral aircraft motion. Flight tests were considered at Mach numbers between 0×3 and 1×3, at altitudes between 1,000ft and 40,000ft and at angles-of- attack vary between 1º and 10º. Following two methods were used to calculate the characteristic system eigenvalues: the approximate method and the exact method. From these eigenvalues, by use of the classic vibration equation, the natural frequencies and damping were determined for the longitudinal and for the lateral aircraft motion(1). In case of the longitudinal aircraft motion, the flying qualities were evaluated for the long and short period of motion, while for the lateral aircraft motion, the flying qualities were evaluated for the roll, Dutch roll and spiral motions. In the following paragraphs, results are presented.

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Volume 111, Number 1119   May 2007

Modelling and vibration of a non-classical tilt-rotor wing system

Authors
O. Song, H. D. Kwon and L. Librescu

Abstract
Problems related with the mathematical modelling and eigenvibration of a tiltrotor aircraft-wing system built up of anisotropic composite materials are investigated. The wing-mounted rotor that can tilt from the vertical position to a horizontal one is modelled and analysed from the vibrational point of view. In this sense, its behaviour is analysed as a function of the mass size, mass moment of inertia, tilt angle and spin speed of the spinning rotor and of its location along the wing span. While the rotor is considered to be rigid, the aircraft wing is modelled as a thin-walled beam that features a doubly-symmetric cross-section contour and incorporates the elastic coupling between flap-lag-transverse shear, on one hand, and between extension-twist, on the other hand. Numerical simulations are provided and pertinent conclusions are outlined.

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Volume 111, Number 1119   May 2007

A change in the calculated impact of supersonic aircraft NOx emissions on the atmosphere

Authors
O. Dessens, H. L. Rogers and J. A. Pyle

Abstract
New model calculations suggest that the potential impact on the atmosphere of a future fleet of supersonic aircraft, for the year 2015, is highly dependent upon the amount of nitrogen oxides (NOx) emitted from the fleet. This result contrasts with the IPCC assessment(1) which suggested that the impact of supersonic aircraft on the atmosphere was primarily through the role of water vapour emissions both on atmospheric ozone and climate change. These new findings are extremely important for atmospheric scientists, the aviation industry and policy makers, highlighting the importance of further development of low NOx combustors for supersonic aircraft, an aspect which has been largely ignored following the IPCC Special Report.

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Volume 111, Number 1119   May 2007

On different parameterisation methods to analyse spacecraft attitude manoeuvres in the presence of attitude constraints

Authors
G. Radice and M. Casasco

Abstract
This paper analyses and compares two different attitude representations, using quaternions and modified Rodrigues parameters, in the context of the potential function method applied to autonomously control constrained attitude slew manoeuvres. This method hinges on the definition of novel Lyapunov potential functions in terms of the attitude parameters representing the current attitude, the goal attitude and any pointing constraints, which may be present. It proves to be successful in forcing the satellite to achieve the desired attitude while at the same time avoiding the pointing constraints. A linearised version of the modified Rodrigues parameterisation is also introduced and analysed. Finally advantages and drawbacks of all attitude representations are discussed.

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Volume 111, Number 1119   May 2007

Modelling and vibration of a non-classical tilt-rotor wing system

Authors
O. Song and H. D. Kwon and L. Librescu

Abstract
Problems related with the mathematical modelling and eigenvibration of a tiltrotor aircraft-wing system built up of anisotropic composite materials are investigated. The wing-mounted rotor that can tilt from the vertical position to a horizontal one is modelled and analysed from the vibrational point of view. In this sense, its behaviour is analysed as a function of the mass size, mass moment of inertia, tilt angle and spin speed of the spinning rotor and of its location along the wing span. While the rotor is considered to be rigid, the aircraft wing is modelled as a thin-walled beam that features a doubly-symmetric cross-section contour and incorporates the elastic coupling between flap-lag-transverse shear, on one hand, and between extension-twist, on the other hand. Numerical simulations are provided and pertinent conclusions are outlined.

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Volume 111, Number 1119   May 2007

Methods for the design of energy efficient high speed aerospace vehicles

Authors
D. Riggins, T. Taylor, L. Terhune and D. Moorhouse†

Abstract
This paper continues development of the fundamental analytical science, methodology and tools required for the analysis, design, and optimisation of high speed aerospace vehicles in terms of the efficient use of on-board energy. Specifically, it presents the complete second-law characterisation and related system-level energy management effectiveness for high-speed vehicles (coupling both aerodynamic and propulsive subsystems). Modelling of the fluid dynamics utilises high-level (multi-dimensional) flow-fields representative of generic configurations of interest. Capability has been recently developed which allows detailed second-law performance audits in terms of the ‘common currency’ of entropy generation for high-speed vehicles (involving complete synthesis of both internal and external flow-fields, i.e. both aerodynamic and propulsive sub-systems). This capability is now extended to encompass and utilise multi-dimensional flow-fields generated by computational fluid dynamics solvers, including Navier-Stokes solvers. Furthermore, the methodology is shown in this paper to provide insight and fundamental direction for management of on-board energy (‘price paid’) for maximum performance missions.

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Volume 111, Number 1119   May 2007

Design of fixed wing micro air vehicles

Authors
P. Cosyn and J. Vierendeels

Abstract
The paper describes the methodology and computational design strategies used to develop a series of fixed wing micro air vehicles (MAVs) at the Ghent University. The emphasis of the research is to find an optimal MAV-platform that is bound to geometrical constraints but superior in its performance. This requires a multidisciplinary design optimisation but the challenges are mainly of aerodynamic nature. Key areas are endurance, stability, controllability, manoeuvrability and component integration. The highly three-dimensional low Reynolds number flow, the lack of experimental databases and analytical or empirical models of MAV-aerodynamics required fundamental research of the phenomena. This includes the use of a vortex lattice method, three-dimensional CFD-computations and a numerical propeller optimisation method to derive the forces and their derivatives of the MAV and propeller for performance and stability-related optimisation studies. The design method leads to a simple, stable and robust flying wing MAV-platform that has the agility of a fighter airplane. A prototype, the UGMAV25, was constructed and flight tests were performed. The capabilities of the MAV were tested in a series of successful flight manoeuvres. The UGMAV15, a MAV with a span of 15cm, is also developed to test flight-qualities and endurance at this small scale. With the current battery technology, a flight-time of at least one hour is expected.

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Volume 111, Number 1119   May 2007

Strategic destruction of the Western commercial aircraft sector: Implications of systems integration and international risk-sharing business models

Authors
D. Pritchard and A. MacPherson

Abstract
This paper offers a critical perspective on the changing organisational structure of the Western commercial aircraft industry. The role of systems integration based on risk-sharing partnerships for new aircraft programmes is explored. We find that build-to-print subcontracting relationships are being replaced by internationally devolved design and engineering tasks for airframe development, signaling a profound change in the geography of commercial aircraft production. While sensible from a financial standpoint, the international outsourcing of design-intensive production entails substantial amounts of technology transfer – including the delivery of proprietary knowledge to risk-sharing partners. For several of the advanced market economies, including Canada, France, Germany, the UK, and the US, the long-range strategic downside is that foreign risk-sharing partners could eventually become competitors. Systems integration on a risk-sharing basis also implies home-country job-losses among skilled workers with expertise in design, engineering, and R&D.

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Volume 111, Number 1119   May 2007

Methods for the design of energy efficient high-speed aerospace vehicles

Authors
D. Riggins, T Taylor, D. Moorhouse and L Tiehune

Abstract

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Volume 111, Number 1119   May 2007

A Changing Impact of Supersonic Aircraft NOx Emissions on the Atmosphere

Authors
O Dessens, H.L. Rogers and J.A. Pyle

Abstract

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Volume 111, Number 1120   June 2007

Addressing pose estimation issues for machine vision based UAV autonomous serial refuelling

Authors
G. Campa, M. R. Napolitano, M. Perhinschi, M. L. Fravolini, L. Pollini and M. Mammarella

Abstract
This paper describes the results of an effort on the analysis of the performance of specific ‘pose estimation’ algorithms within a Machine Vision-based approach for the problem of aerial refuelling for unmanned aerial vehicles. The approach assumes the availability of a camera on the unmanned aircraft for acquiring images of the refuelling tanker; also, it assumes that a number of active or passive light sources – the ‘markers’ – are installed at specific known locations on the tanker. A sequence of machine vision algorithms on the on-board computer of the unmanned aircraft is tasked with the processing of the images of the tanker. Specifically, detection and labeling algorithms are used to detect and identify the markers and a ‘pose estimation’ algorithm is used to estimate the relative position and orientation between the two aircraft. Detailed closed-loop simulation studies have been performed to compare the performance of two ‘pose estimation’ algorithms within a simulation environment that was specifically developed for the study of aerial refuelling problems. Special emphasis is placed on the analysis of the required computational effort as well as on the accuracy and the error propagation characteristics of the two methods. The general trade offs involved in the selection of the pose estimation algorithm are discussed. Finally, simulation results are presented and analysed.

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Volume 111, Number 1120   June 2007

Three-dimensional indicial response of finite aspect ratio yawed wings

Authors
C. E. Manglano-Villamarin and S. T. Shaw

Abstract
The influence of finite aspect ratio and yaw on the computed indicial response of a pitching wing has been studied using numerical solutions of the unsteady Euler equations. The indicial response was obtained directly from computations of the unsteady flow around two- and three-dimensional wings subjected to a step change in incidence at Mach numbers between 0×2 and 0×7. The data reveal several important characteristics in the behaviour of the unsteady response of three-dimensional wings. The initial response is shown to be independent of both aspect ratio and yaw confirming the results of linearized theory. During the subsequent development of the unsteady response significant differences are observed between the two- and three-dimensional behaviours as a consequence of changes to both wing aspect ratio and yaw angle. The formation and spanwise propagation of acoustic waves due to finite aspect ratio is shown to have a significant influence on the development of the unsteady forces, while for yawed wings the results indicate that the manner in which the windward and leeward tip vortices form is important. Based upon these observations it is suggested that the current practice within the rotorcraft community in which two-dimensional indicial response functions are employed may be unreliable for the advancing blade.

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Volume 111, Number 1120   June 2007

Investigation on the aerodynamic performance of an ejection seat

Authors
1,2D. H. Chen, 1,2W. H. Wu, 1J. J. Wang and 2Y. Huang

Abstract
A unique experimental method is used, in combination with numerical calculation and engineering estimation, to study the aerodynamic performance of an ejection seat at M = 0×60, 0×90 and 1×20, angles-of-attack a = 0°~360°, and sideslip angles b = 0°~–90°. Several basic characteristics of the aerodynamic performance are explored. The normal force of the ejection seat varies in a sinusoidal way and the axial force in a cosinoidal way, with the angle-of-attack. The model is statically unstable longitudinally at most attitude angles and the longitudinal stability could be improved by a stabiliser. These characteristics result from a large low pressure area caused by the leeward separation and the windward high pressure area in the ejection seat flow field, at all a, due to the blunt configuration. A set of engineering calculation formulae is deduced, based on the aerodynamic characteristics of the ejection seat.

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Volume 111, Number 1120   June 2007

A proposed reference framework for unmanned aerial vehicle and system airworthiness requirements

Authors
A. Maneschijn, T. Jones, T. W. von Backström and L. A. Ingham

Abstract
Various programmes are underway internationally to establish legislative instruments for regulating civil and military unmanned aerial vehicles and systems. An analysis of a selection of these programmes revealed that the approaches used for airworthiness regulation are not harmonised and are usually limited to specific unmanned aerial vehicle types, indicating the need for a generic framework for airworthiness requirements. A functional Reference Framework for unmanned aerial vehicle and system airworthiness requirements was developed using Annex 8 of the Chicago Convention as a reference basis, supplemented with airworthiness procedures and functional requirements derived from manned aircraft regulations, unmanned aerial vehicle and system airworthiness material, and flightworthiness guidelines for reusable launch vehicles. Various airworthiness elements were identified for which further research is required to develop appropriate airworthiness requirements. This paper summarises the development of the framework and proposes the Reference Framework as a functional basis for generating comprehensive South African civil and military airworthiness requirements for unmanned aerial vehicles and systems.

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Volume 111, Number 1120   June 2007

Use of Global Positioning System velocity outputs for determining airspeed measurement error

Authors
G. B. Gratton

Abstract
Several methods have been derived since the advent of GPS (Global Positioning System) receivers in aircraft cockpits by which these receivers may be used to calibrate these aircraft’s other instrumentation; in particular the pitot-static system. This paper presents the four most suitable methods, two of which have been developed by the author. These methods are shown with a common symbology, and their strengths, weaknesses, analysis and operational use are compared.

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Volume 111, Number 1121   July 2007

Performance characterisation of MPD thrusters

Authors
T. R. Nada

Abstract
This paper introduces a characterisation of the performance indices and operating limits of the self field magnetoplasmadynamic thruster. The thrust, specific impulse, and efficiency are considered as the main performance indices, while the operating limits are the cathode lifetime, onset phenomenon, and the overfed state of the thruster. The effects of thruster parameters (current, mass flow rate, geometry, and propellant type) on the performance indices and operating limits are examined using one-dimensional model of cylindrical self-field thrusters. Design charts are presented to help the designers to choose the optimum and safe set of the thruster parameters that realise certain mission requirements.

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Volume 111, Number 1121   July 2007

Towards a full two dimensional gas turbine performance simulator

Authors
V. Pachidis, P. Pilidis, L. Marinai, I. and Templalexis

Abstract
In commercially available gas turbine performance simulation tools, individual engine components are typically represented with non-dimensional maps of experimental or default data. In those cases where actual component characteristics are not available and default characteristics are used instead, conventional tools can deviate substantially at off-design and transient conditions. Similarly, when real component characteristics are available, conventional engine cycle simulation tools can not predict the performance of the engine at other than nominal conditions satisfactorily, or account for the impact of changes in component geometry. This study looked into the full integration of two-dimensional streamline curvature component models with a low fidelity cycle program. Firstly, the obtained engine performance was compared against the one calculated based on default component characteristics. As a second case study, a range of flight Mach numbers and angles of attack were examined together with the effect of three different intake lip geometries on the performance of a notional, two-spool, low-bypass ratio, military engine. Two-dimensional models were used in the engine cycle analysis to provide a more accurate, physics- and geometry-based estimate of intake and fan performances. The analysis carried out by this study demonstrated relative changes in the predicted engine performance larger than 1%. For briefness, representative results are presented and discussed in this paper for one flight Mach number and angle of attack setting. More importantly, this research effort established the necessary methodology and technology required towards a full, two-dimensional engine cycle analysis at an affordable computational resource in the very short term.

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Volume 111, Number 1121   July 2007

Aircraft cost modelling using the genetic causal technique within a systems engineering approach

Authors
R. Curran, S. Castagne, J. Early, M. Price, S. Raghunathan, J. Butterfield and A. Gibson

Abstract
The paper is primarily concerned with the modelling of aircraft manufacturing cost. The aim is to establish an integrated life cycle balanced design process through a systems engineering approach to interdisciplinary analysis and control. The cost modelling is achieved using the genetic causal approach that enforces product family categorisation and the subsequent generation of causal relationships between deterministic cost components and their design source. This utilises causal parametric cost drivers and the definition of the physical architecture from the Work Breakdown Structure (WBS) to identify product families. The paper presents applications to the overall aircraft design with a particular focus on the fuselage as a subsystem of the aircraft, including fuselage panels and localised detail, as well as engine nacelles. The higher level application to aircraft requirements and functional analysis is investigated and verified relative to life cycle design issues for the relationship between acquisition cost and Direct Operational Cost (DOC), for a range of both metal and composite subsystems. Maintenance is considered in some detail as an important contributor to DOC and life cycle cost. The lower level application to aircraft physical architecture is investigated and verified for the WBS of an engine nacelle, including a sequential build stage investigation of the materials, fabrication and assembly costs. The studies are then extended by investigating the acquisition cost of aircraft fuselages, including the recurring unit cost and the non-recurring design cost of the airframe sub-system. The systems costing methodology is facilitated by the genetic causal cost modeling technique as the latter is highly generic, interdisciplinary, flexible, multilevel and recursive in nature, and can be applied at the various analysis levels required of systems engineering. Therefore, the main contribution of paper is a methodology for applying systems engineering costing, supported by the genetic causal cost modeling approach, whether at a requirements, functional or physical level.

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Volume 111, Number 1121   July 2007

The representation of GT component maps using Mach numbers

Authors
V. E. Kyritsis, P. Pilidis and K. Ramsden

Abstract
Component maps are produced under certain environmental conditions using air as the working fluid during static ground operation. Any changes of the component characteristics when operating under different temperature conditions and/or with different working fluid are partially taken into account, because of the existence of the gas constant and the ratio of the specific heats in the non-dimensional mass flow and rotational speed. This provides a second order correction for the component characteristics, which may be adequate for the initial modeling of engines. However, for rigorous performance calculations correction factors are applied to the non-dimensional mass flow, rotational speed and pressure ratio distributions of a map, when deviations from the reference conditions under which it was extracted, are experienced. In the current study, a different approach is considered in order to eliminate the inaccuracies caused by the varying temperature and chemical composition. It makes direct use of inlet and circumferential Mach numbers based upon stagnation temperature in conjunction with dimensionless enthalpy variation. A sensitivity analysis against gas property variations is conducted to quantify the benefits gained in precision. Generally, the well-known relationships correlating the Mach number with total and static properties are based on the assumption of perfect gas and constant gas properties. Introducing dependency on temperature and/or chemical composition for the caloric properties of the semi-perfect gas, proper mean values are defined and some theoretical corrections are provided for the well-known equations. The mass flow compatibility equation is then based on the ‘corrected’ expression correlating dimensionless mass flow and Mach number and takes full account of gas property variations.

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Volume 111, Number 1121   July 2007

Dynamic gain scheduled control of a Hawk scale model

Authors
T. Richardson, M. Lowenberg, C. Jones and A. Dubs

Abstract
When designing flight control laws using linearisations of an aircraft model about different flight conditions, some form of scheduling of the resultant gains will often be required to implement the controller over wide operating regions. In practice, the controller gains are often scheduled against relatively slowly-varying system states such as altitude or velocity. However, it may also be desirable to schedule gains against rapidly-varying states such as angle-of-attack, thereby generating a cyclic dependence through hidden coupling terms. Previous published work at Bristol has developed a numerical method of accounting for this dependence when scheduling state feedback gains against coupled states. The resulting `dynamic gain schedule’ is shown to significantly improve the transient response of the aircraft model during rapid manoeuvring and to reduce the chances of control surface actuator position limit saturation. In this paper, the novel design process, using eigenstructure assignment, is applied to a mathematical second-order longitudinal aircraft model which represents an approximate BAe Hawk wind-tunnel model. The dynamic gain scheduled controller is shown to work extremely well in practice when applied to the closed-loop experimental rig. Despite the highly nonlinear characteristics of the model aerodynamics and tailplane actuation system, as well as unmodelled high turbulence levels, dynamic gain scheduling demonstrates stable closed loop control even in regions where the nonlinearities are such that conventional gain scheduling fails to produce a stable response.

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Volume 111, Number 1121   July 2007

A static compressible flow model of synthetic jet actuators

Authors
H. Tang and S. Zhong

Abstract
In this paper, a simple static compressible flow model for circular synthetic jet actuators is described. It is used to undertake a systematic computational investigation of the effect of changing actuator geometrical and operating parameters on the magnitude of peak jet velocity at the orifice exit of an actuator whose diaphragm displacement and frequency are allowed to vary independently. It is found that, depending on the flow conditions inside the orifice duct, the actuator may operate in two distinct regimes, i.e. the Helmholtz resonance regime and the viscous flow regime. In the Helmholtz resonance regime, the resultant synthetic jet is generated by the mass physically displaced by the oscillating diaphragm coupled with the Helmholtz resonance in the actuator. In the viscous flow regime, the Helmholtz resonance is completely damped by viscous effect such that the jet is produced by the diaphragm oscillation alone. The relationship between actuator geometrical and operating parameters at the optimum condition which yields the maximum peak jet velocity at a given diaphragm displacement is also established for these two regimes. Finally, a preliminary procedure for designing synthetic jet actuators for flow separation control on an aircraft wing is proposed.

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Volume 111, Number 1122   August 2007

The Victoria University of Manchester’s contributions to the development of aeronautics

Authors
J. A. D. Ackroyd

Abstract
This issue of the Aeronautical Journal celebrates the 50th anniversary of the foundation of the Honours Degree Course in Aeronautical Engineering at the Victoria University of Manchester. The following article therefore describes the aeronautical research and teaching activities of that university up to its recent amalgamation with the University of Manchester Institute of Science and Technology (UMIST) to form the present-day University of Manchester. This juncture provides a further justification for recording the Victoria University’s achievements. Both the Victoria University and UMIST had their roots in the nineteenth century although, apart from the relatively brief period of the First World War, neither of them was particularly involved in aeronautics until after the Second World War. However, as Sections 6.0-10.0 seek to demonstrate, thereafter the Victoria University’s involvement became considerable. The preceding Sections describe the origins of the Victoria University and UMIST and, in the case of the former institution, the subsequent activities of its staff and graduates in engineering and mathematics which, although not always specifically aeronautical in content, nonetheless had a profound influence on the development of the aeronautical sciences.

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Volume 111, Number 1122   August 2007

A review of some current research on pressure sensitive paint and thermographic phosphor techniques

Authors
K. Kontis

Abstract
The paper discusses the development and application activities within the Aero-Physics and Measurement Technology Laboratory at the University of Manchester on pressure sensitive paint and thermographic phosphor optical imaging systems for gas dynamic applications. It provides a brief review of the basic principles, fundamental theory, properties, chemical characteristics and bonding technologies associated with the two systems. A number of case studies are presented, which exhibit the range of applicability, limitations and potential for further development of the technologies.

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Volume 111, Number 1122   August 2007

On the benefits of lower Mach number aircraft cruise

Authors
A. Filippone

Abstract
The paper reviews the issue of cruise Mach number and addresses the benefits of operating subsonic commercial aircraft at speeds below the long-range cruise speed. The case considered is the flight of transport aircraft for flight segments up to 1,000nm. It is shown that the fuel burned is decreased by as much as 1×8% on a nominal 1,000nm stage length for operation around the long-range cruise Mach number, or below. This is achieved at a cost of a marginal delay on each flight segment (less than three minutes). The longer flight time is likely not to affect the daily operation of the aircraft. The fuel saving is compounded, because the gross take-off weight (GTOW) is recalculated to take into account the reduced fuel consumption at each flight segment. The analysis into the environmental benefits includes the reduction in,andemissions, and the heat released in the high atmosphere. Sensitivity analyses are carried out on the take-off weight, on the aerodynamic coefficients, on the transonic drag rise and the weight uncertainty. It is predicted that the optimal operation of the example aircraft over a nominal 1,000nm route can reduce the fuel consumption by as much as 150,000kg per year in comparison with an operation at the long-range Mach number. The aircraft model has a maximum take-off weight of 170,000kg and is powered by two GE CF6-80C2 engines.

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Volume 111, Number 1122   August 2007

Three-dimensional tensile stress concentration in countersunk rivet holes

Authors
Anil Bhargava and Kunigal N. Shivakumar†

Abstract
A detailed and accurate three-dimensional finite element stress analysis was conducted on countersunk rivet holes in a plate subjected to tension loading. The analysis included a wide range of countersunk depths, plate thicknesses, countersunk angles and plate widths. The study confirmed some of the previous results, addressed their differences, provided many new results, and investigated countersunk angle and width effects. Using the detailed FE results and the limiting conditions, a design equation for stress concentration was developed and verified.

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Volume 111, Number 1122   August 2007

Application of synthetic jet actuators for the modification of the characteristics of separated shear layers on slender wings

Authors
M. Watson, A. J. Jaworski and N. J. Wood

Abstract
This paper presents an experimental investigation related to controlling the unsteady characteristics of the separated shear layers occurring over highly swept wings, and in particular focuses on application of synthetic jet actuators for modification of unsteady dynamic loading on the wing surface due to the phenomenon referred to as vortex breakdown (vortex burst). In the post burst flow region the surface pressure measurements reveal the presence of certain characteristic spectral peaks that are thought to represent the presence of a spiralling filament of vorticity inside the expanded vortex that is known to be present in the burst flow over swept wings. This paper details an investigation into how the use of an array of 18 discrete synthetic jet actuators, distributed along the leading edge of a delta wing with a 60° sweep angle, can be used to alter the spectral content of this unsteadiness and reduce the level of unsteady pressure found in the post-burst region toward the wing trailing edge by up to 40%. Measurements of the surface pressure spectral distributions over the wing are presented together with PIV measurements of the vortex cross-section, conducted in the successive planes parallel to the wing trailing edge. Additional surface flow visualisation indicates that the effect of the actuators on the leading edge boundary layer is to induce local separation delays close to each actuator orifice, which introduce ‘ripples’ into the shear layer as it separates. The results obtained are used to formulate an interpretative hypothesis attempting to explain the mechanisms responsible for modification of the spectral content and the level of excitation measured on the wing surface.

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Volume 111, Number 1123   September 2007

Developments in RF simulator technology

Authors
M. Pywell

Abstract
Technology developments in radar frequency simulators of the type used to verify the performance of complex electronic warfare systems are described. The successful verification of this performance prior to combat use is a necessary pre-requisite of military platform survivability and mission success. These simulators and associated modelling and analysis tools have enabled a major shift during the last 15 years from expensive and limited flight trials to repeatable laboratory and anechoic chamber tests, although they will never totally supplant those trials. Most limitations of the early days of many-channel simulators, 25 years ago, have been resolved or adequately and – as importantly – affordably mitigated, largely enabled by computing power increases. Limitations remain that will, within affordability constraints driven by Defence Ministries world-wide, prevent perfect simulation (‘emulation’) and the attendant, tantalising but utopian goal of laboratory and chamber test results that precisely match those from flight test and combat.

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Volume 111, Number 1123   September 2007

‘Greener’ civil aviation using air-to-air refuelling – relating aircraft design efficiency and tanker offload efficiency

Authors
R. K. Nangia

Abstract
The aircraft industry, as a whole, is striving to limit its impact on the environment. Improved engine design and operation may offer a reduction in emissions of a few percent. More efficient air traffic control (ATC) may offer a limited reduction in overall fuel burn. Improvements in aerodynamic design and materials available (e.g. on A350XWB, B787) might achieve a few percent increases in efficiencies. The use of alternative fuels is some way off. The ACARE objectives present a stiff challenge. Our recent studies have shown that air-to-air-refuelling (AAR), well established in military circles, introduced to civil aircraft operations would provide fuel savings of the order of 30% – 40%. AAR will allow smaller (3,000nm range), more efficient (greener) aircraft, operating from shorter runways, to fulfil long-range route requirements. In addition, the ‘safety-net’ afforded by the availability of AAR will enable a host of hitherto borderline technologies to be accepted and utilised in future aircraft designs. Laminar flow will provide fuel savings and increased efficiency in its own right provided it is enabled within a civil AAR environment. Similarly, supersonic transport becomes an acceptable economic option. As a result of our previous publication in the RAeS The Aeronautical Journal, November 2006(1), a few more interesting aspects have emerged with regard to tanker design and operation and the magnitude of the fuel off-loads available and relating them to overall fuel savings and gains in payload range efficiency (PRE).

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Volume 111, Number 1123   September 2007

Some analytical and numerical solutions for the safe turn manoeuvres of agricultural aircraft – an overview

Authors
B. Rasuo

Abstract
In this paper, a theoretical study of the turn manoeuvre of an agricultural aircraft is presented. The manoeuvre with changeable altitude is analyzed, together with the, effect of the load factors on the turn manoeuvre characteristics during the field-treating flights. The mathematical model used describes the procedure for the correct climb and descent turn manoeuvre. For a typical agricultural aircraft, the numerical results and limitations of the climb, horizontal and descending turn manoeuvre are given. The problem of turning flight with changeable altitude is described by the system of differential equations which describe the influence of the normal and tangential load factors on velocity, the path angle in the vertical plane and the rate of turn, as a function of the bank angle during turning flight. The system of differential equations of motion was solved on a personal computer with the Runge-Kutta-Merson numerical method. Some analytical and numerical results of this calculation are presented in this paper.

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Volume 111, Number 1124   October 2007

Modelling the interaction of helicopter main rotor and tail rotor wakes

Authors
T. M. Fletcher and R. E. Brown

Abstract
The mutual interaction between the main rotor and tail rotor wakes is central to some of the most problematic dynamic phenomena experienced by helicopters. Yet achieving the ability to model the growth and propagation of helicopter rotor wakes with sufficient realism to capture the details of this interaction has been a significant challenge to rotorcraft aerodynamicists for many decades. A novel computational fluid dynamics code tailored specifically for rotorcraft applications, the vorticity transport model, has been used to simulate the interaction of the rotors of a helicopter with a single main rotor and tail rotor in both hover and low-speed quartering flight, and with the tail rotor rotating both top-forward and top-aft. The simulations indicate a significant level of unsteadiness in the performance of both main and tail rotors, especially in quartering flight, and a sensitivity to the direction of rotation of the tail rotor. Although the model thus captures behaviour that is similar to that observed in practice, the challenge still remains to integrate the information from high fidelity simulations such as these into routine calculations of the flight dynamics of helicopters.

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Volume 111, Number 1124   October 2007

An optimal-fuzzy two-phase CLOS guidance law design using ant colony optimisation

Authors
H. Nobahari and S. H. Pourtakdoust

Abstract
The well-known ant colony optimisation (ACO) meta-heuristic is applied to optimise the parameters of a new fuzzy command to line-of-sight (CLOS) guidance law. The new guidance scheme includes two phases, a midcourse and a terminal phase. In the first phase, a lead strategy is utilised which reduces the acceleration demands. A proportional derivative (PD) fuzzy sliding mode controller is used as the main tracking controller of the first phase. Moreover, a supervisory controller is coupled with the main tracking controller to guarantee the missile flight within the beam. In the terminal phase, a pure CLOS guidance law without lead angle is utilised. For this phase, a new hybrid fuzzy proportional-integral-derivative (PID) fuzzy sliding mode controller is proposed as a high precision tracking controller. The parameters of the proposed controllers for the first and the second phases are optimised using ACO. In this regard, the recently developed continuous ant colony system (CACS) algorithm is extended to multi-objective optimisation problems and utilised to optimise the parameters of the pre-constructed fuzzy controllers. The performance of the resulting guidance law is evaluated at different engagement scenarios and compared with the well-known feedback linearisation method. The comparison is also made in the presence of measurement noise.

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Volume 111, Number 1124   October 2007

Estimation of lateral-directional parameters using neural networks based modified delta method

Authors
S. Singh and A. K. Ghosh

Abstract
The aim of the study described herein was to develop and verify an efficient neural network based method for extracting aircraft stability and control derivatives from real flight data using feed-forward neural networks. The proposed method (Modified Delta method) draws its inspiration from feed forward neural network based the Delta method for estimating stability and control derivatives. The neural network is trained using differential variation of aircraft motion/control variables and coefficients as the network inputs and outputs respectively. For the purpose of parameter estimation, the trained neural network is presented with a suitably modified input file and the corresponding predicted output file of aerodynamic coefficients is obtained. An appropriate interpretation and manipulation of such input-output files yields the estimates of the parameter. The method is validated first on the simulated flight data using various combinations and types of real-flight control inputs and then on real flight data. A new technique is also proposed for validating the estimated parameters using feed-forward neural networks.

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Volume 111, Number 1124   October 2007

Survivability of helicopter with individual blade primary control failure

Authors
R. Ganguli, B. Jehnert, J. Wolfram and P. Voersmann

Abstract
The effect of actuator damage on a helicopter rotor with an IBC based primary control system is studied. Such a system eliminates the swashplate and can be accomplished by trailing-edge flaps, active twist or full authority IBC, especially with smart material actuators. Damage to the collective, longitudinal and lateral cyclic are simulated for one blade, both individually and in combinations ranging from partial damage to complete failure. Numerical results are obtained using a dissimilar blade aeroelastic analysis based on finite elements in space and time for hover and forward speed conditions. It is found that the helicopter can be trimmed for all cases with all three controls having failed on the blade with actuator damage thereby showing that the IBC actuated rotor can survive an actuator failure and can be reconfigured by the pilot using the controls on the other blades. However, in case the collective fails and the longitudinal cyclic is present, there are problems in achieving trim at high damage levels at high forward speeds. Physical explanations of this phenomenon are given. The response (especially flap) for the damaged rotor blades can become high and 1/rev and 2/rev are transmitted by the reconfigured rotor to the hub. Results show that IBC based primary controls provide redundancy which can improve the survivability of a helicopter in case of actuator failure in one blade.

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Volume 111, Number 1124   October 2007

Scramjets

Authors
M Smith

Abstract
The supersonic combustion ramjet, or scramjet, is the engine cycle most suitable for sustained hypersonic flight in the atmosphere. This article describes some of the challenges facing scramjet designers, and the methods currently used for the calculation of scramjet performance. It then reviews the HyShot 2 and Hyper-X flight programs as examples of how sub-scale flights are now being used as important steps towards the development of operational systems. Finally, it describes some recent advances in three-dimensional scramjets with application to hypersonic cruise and multi-stage access-to-space vehicles.

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Volume 111, Number 1125   November 2007

Effect of plunging amplitude on the performance of a wind turbine blade section

Authors
M. R. Soltani and F. Rasi Marzabadi

Abstract
Extensive low speed wind-tunnel tests were conducted to study the unsteady aerodynamic behaviour of an airfoil sinusoidally oscillating in plunge. The experiments involved measuring the surface pressure distribution over a range of amplitudes, H = ±5 to ±15cm. In addition, steady state data were acquired and were used to furnish a baseline for further analysis and comparison. The model was oscillated with a constant reduced frequency, k = 0·058, at three mean angles of attack of 0º, 10º and 18º.The unsteady aerodynamic loads were calculated from the surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. The plunging displacements were transformed into the equivalent angle-of-attack. Variations of the pressure coefficients and aerodynamic loads with the equivalent angle-of-attack showed strong sensitivity to the plunging amplitude and also to the mean angles-of-attack.

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Volume 111, Number 1125   November 2007

Remarks on the nonlinear dynamics of a typical aerofoil section in dynamic stall

Authors
U. Galvanetto, J. Peirò and C. Chantharasenawong

Abstract
We use standard tools of the theory of dynamical systems such as phase plots, bifurcation diagrams and basins of attraction to analyse and understand the dynamic behaviour of a typical aerofoil section under dynamic stall conditions. The structural model is linear and the aerodynamic loading is represented by the Leishman-Beddoes semi-empirical dynamic stall model. The loads given by this model are non-linear and non-smooth, therefore we have integrated the equation of motion using a Runge-Kutta-Fehlberg (RKF45) algorithm equipped with event detection. We perform simulations of the motion for a range of Mach numbers and show that the model is very sensitive to small variations. This is evidenced by the presence in the bifurcation diagram of co-existing attractors or, in other words, by the existence of more than one steady-state motion for a given Mach number. The mechanisms for the appearance and disappearance of the co-existing attractors are elucidated by analysing the evolution of their basins of attraction as the Mach number changes.

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Volume 111, Number 1125   November 2007

Experimental and computational study of unsteady hypersonic cavity flows

Authors
S. Creighton and R. Hillier

Abstract
This paper presents a combined experimental and computational study of annular cavities on a semi-angle cone in a Mach 8·9 flow. A range of cavity length-to-depth ratios has been considered, and a parameter has been determined that distinguishes between ‘weak oscillations’ and ‘strong oscillations’ of the cavity flow. Essentially the work identifies the transition from the case where the flow can be regarded as ‘pure cavity flow’ to that where the flow behaviour is tending towards that of a ‘spiked blunt body’. The CFD simulations also suggest that, for a certain range of cavity scale, the limiting cavity flow state depends upon the flow initialisation process; it may be weak or strongly oscillating.

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Volume 111, Number 1125   November 2007

Prediction of drag and lift of wings from velocity and vorticity fields

Authors
G. Zhu, P. W. Bearman and J. M. R. Graham

Abstract
The present paper continues the work of Zhu et al(9). The closed-form expressions for the evaluation of forces on a body in compressible, viscous and rotational flow derived in the previous paper have been extended to different forms. The expressions require only a knowledge of the velocity field (and its derivatives) in a finite and arbitrarily chosen region enclosing the body. The equations are implemented on three-dimensional inviscid flows over wings and wing/body combinations. Further implementation on three-dimensional viscous flows over wings has also been investigated.

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Volume 111, Number 1125   November 2007

Experimental and computational study of unsteady hypersonic cavity flows

Authors
S. Creighton and R. Hillier

Abstract
This paper presents a combined experimental and computational study of annular cavities on a semi-angle cone in a Mach 8·9 flow. A range of cavity length-to-depth ratios has been considered, and a parameter has been determined that distinguishes between ‘weak oscillations’ and ‘strong oscillations’ of the cavity flow. Essentially the work identifies the transition from the case where the flow can be regarded as ‘pure cavity flow’ to that where the flow behaviour is tending towards that of a ‘spiked blunt body’. The CFD simulations also suggest that, for a certain range of cavity scale, the limiting cavity flow state depends upon the flow initialisation process; it may be weak or strongly oscillating.

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Volume 111, Number 1125   November 2007

Reducing environmental impacts of aviation with innovative air traffic management technologies

Authors
V. Williams, R. B. Noland, A. Majumdar, R. Toumi†, W. Ochieng and J. Molloy

Abstract
Commercially-driven air traffic management (ATM) innovations typically aim to increase air space capacity and/or reduce delays. Here, their potential application for environmental mitigation is discussed. Both carbon dioxide (CO2) and non-CO2 climate impacts are considered, as are noise and air quality issues. We outline the technological, scientific and political barriers to an integrated approach to applying ATM technologies to environmental mitigation. These issues highlight the need to improve comparison and prioritisation of the emissions and effects of aviation.

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Volume 111, Number 1125   November 2007

Large-eddy simulation of separated flow over a swept wing with approximate near-wall modelling

Authors
N. Li and M. A. Leschziner

Abstract
The paper investigates, by means of a simulation methodology, the flow separating from a 40 degrees backward-swept wing at 9 degrees incidence and Reynolds number of 210,000, based on the wing-root chord length. The Simulation corresponds to LDA, PIV and suction-side-topology measurements for the same geometry, conducted by other investigators specifically to provide validation data. The finest block-structured mesh contains 23·6 million nodes and is organised in 256 blocks to maximise mesh quality and facilitate parallel solution on multi-processor machines. The near-wall layer is resolved, to a thickness of about y+ = 20, by means of parabolised URANS equations that include an algebraic eddy-viscosity model and from which the wall-shear stress is extracted to provide an unsteady boundary condition for the simulation. The numerical solution is in good agreement with the experimental behaviour over the 50-70% inboard portion of the span, but the simulation fails to resolve some complex features close to the wing tip, due to a premature leading-edge vortex breakdown and loss in vortex coherence. The comparisons and their discussion provide useful insight into various physical characteristics of this complex separated wing flow.

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Volume 111, Number 1125   November 2007

Flow control with active dimples

Authors
S. Dearing, S. Lambert and J. Morrison

Abstract
The long-term goal is to design and manufacture optimal ‘on-demand’ vortex generators, ‘dimples’ that can produce vortices of prescribed strength and duration for the real-time control of aerodynamic flows that are either undergoing transition or are fully turbulent, attached or separating. Electro-active polymers (EAP) are ideal for a dimple control surface, offering high strain rate, fast response, and high electromechanical efficiency. EAP can also be used as the basis of a resistanc – or capacitance – change pressure sensor, development of which has just begun. In terms of manufacture, inkjet printing of EAP also offers a paradigm shift such that a monolithic control surface is a very real possibility. Important features for integration into a control system are robustness and a predictable, repeatable motion. With these objectives in mind, the suitability of EAP-based actuators is assessed both mechanically and aerodynamically. The ultimate goal is to integrate these devices, along with shear-stress and pressure sensors and distributed control, also under development, into a flexible ‘smart skin’ which could be incorporated into an airframe structure. The response of a laminar boundary layer to forcing is investiagted using mechanical dimples.

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Volume 111, Number 1126   December 2007

A review of supersonic business jet design Issues

Authors
H. Smith

Abstract
Key issues relating to the Supersonic Business Jet (SBJ) concept are reviewed with the intent to assess the readiness of enabling technologies and hence the concept itself. The multidisciplinary nature of aircraft design precludes an in-depth analysis of each specific aspect, which could individually be the subject of a separate discipline review, hence an overview is presented. The review looks at the market, environmental issues, with particular reference to the sonic boom phenomenon & solutions, technological issues, including prediction methods, flight testing, systems, certification and interested aerospace companies and design organisations. It is apparent that the need to reduce the sonic boom signature is vital if the vehicle is to be permitted to operate over land and hence be economically viable. It is clear that sonic boom acceptability requirements must be set if resources are to be effectively focused and designs are to converge. Despite this challenge, considerable investment is aimed at de-risking many of the enabling technologies and raising readiness levels. Many technologies are moving beyond theoretical and numerical analysis into the experimental and flight test domains. Collaboration between the civil and military sectors is increasing. Clearly, supersonic air travel is not an efficient means of personal conveyance; however, concerns for the environment are difficult to balance against the ‘value of time’ benefits offered by the SBJ concept. Air travel, of which this is a specialised form, is important to the global economy. Continued effort in the areas of human factors, customer demand and certification & requirements would be beneficial.

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Volume 111, Number 1126   December 2007

Flight data reduction methodology for performance evaluation and comparison of model-following adaptive control laws

Authors
M. G. Perhinschi and M. R. Napolitano

Abstract
Even small differences in atmospheric and/or flight conditions can potentially impact significantly the evaluation of the performance of the control laws and prevent a correct comparison, especially in the case of reduced size aircraft (autonomous or remotely piloted). Consistent deterministic control inputs can only be guaranteed through some form of computer-based on-board excitation system. In this paper, a methodology is proposed for flight data reduction with the purpose of accounting for non-homogeneous atmospheric conditions and inconsistent pilot inputs. The method is developed for the specific purpose of comparing model-following adaptive control laws. Performance evaluation parameters based on angular rate tracking errors are defined and used for the comparison. As a result of this approach, an additive correction is applied to the angular rate measurements to compensate for non-homogeneous turbulence effects. A multiplicative correction factor is applied to the angular rate tracking error to take into account non-identical pilot inputs. The procedure is validated with simulation and flight data obtained in the process of designing a set of fault tolerant control laws based on non-linear dynamic inversion with neural network augmentation for the reduced size WVU YF-22 aircraft model.

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Volume 111, Number 1126   December 2007

Three-dimensional tensile stress concentration in countersunk rivet holes

Authors
A. Bhargava and K. N. Shivakumar†

Abstract
A detailed and accurate three-dimensional finite element stress analysis was conducted on countersunk rivet holes in a plate subjected to tension loading. The analysis included a wide range of countersunk depths, plate thicknesses, countersunk angles and plate widths. The study confirmed some of the previous results, addressed their differences, provided many new results, and investigated countersunk angle and width effects. Using the detailed FE results and the limiting conditions, a design equation for stress concentration was developed and verified.

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Volume 111, Number 1126   December 2007