BAE Systems's Taranis UCAV flying in full-up stealth mode at an 'undisclosed location'. (BAE Systems)
Engineers working on the BAE Systems’ Taranis stealth UCAV demonstrator faced a number of unique aerodynamic challenges which are described in a recent Aeronautical Journal paper. BILL READ explains.
“You have turned the ‘theoretically possible’ into the ‘practically achievable’. Very few people have made such a contribution to the world of aviation over the decades. I hope that we will be allowed to tell the world about it at some stage.” These were the words of Nigel Whitehead, Group Managing Director – Programmes and Support, BAE Systems, in a message to members of BAE’s flight controls and air data team following the 2013 flight trials of the Taranis stealth UCAV demonstrator aircraft
The August issue of The Aeronautical Journal, the technical and research journal published by the RAeS includes a paper from Chris Lee of BAE Systems on the development of Taranis by BAE Systems Military Air & Information (MAI) at Warton. In the paper, Lee reviews the pioneering aerodynamic research to develop the Taranis low-observable design, not just from a technical viewpoint but also in the wider context of the UK’s evolving combat aircraft aerodynamic capability.
Maintaining the legacy of British combat aviation
Much as EAP led to the Eurofighter Typhoon, so the Taranis is paving the way for a future combat aircraft. (BAE Systems).
In the paper, Lee examines the aerodynamic evolution of Taranis through the development of the Canberra, Lightning, TSR2, Harrier, Jaguar, Tornado and Eurofighter. Placing Taranis in a historical context, Lee quotes from a book written in 1916 by aerodynamic engineer and RAeS fellow FW Lanchester entitled Aircraft in Warfare, the Dawn of the Fourth Arm in which he writes: “The supremacy of British aircraft can only be maintained by the adoption of a thoroughly progressive constructional policy, guided constantly by the most recent scientific discovery and research, and by utilising to the full information and experience gained in the Services.” Lee argues that the recent flight trials of Taranis provide evidence of that continued capability.
When working on Taranis, BAE Systems MAI had to find a trade-off between a number of conflicting requirements. To fulfil it its mission function, the demonstrator had to have a shape and size for powerplant and operating systems but, at the same time, to have a low observability (LO), or ‘stealth’, signature to avoid detection. Severely constrained stabilisation and control surfaces meant that the aerodynamic shape of the aircraft was inherently unstable but yet still had to be capable of controlled flight.
To analyse the aerodynamics of the airframe, Lee describes how the Taranis design team compiled a detailed description of the aircraft’s stability and control characteristics based on wind-tunnel data, CFD analysis and empirically-derived datasheets. The LO requirements for Taranis precluded the use of conventional air data measurement techniques and a novel air data system was developed which was tested in initial flight trials together with an air data noseboom. Once the team were confident in the behaviour of the novel system, the flight trials were completed with the noseboom removed.
Lee also describes the challenges the designers encountered in designing an engine air induction system which met the requirements for low observability (LO) while ‘transgressing all the established principles of good intake aerodynamic design’. The engine exhaust solution developed for Taranis set further challenges for propulsion integration aerodynamics. While the relatively high aspect ratio rectangular exit was easier to integrate into the ‘flying wing’ Taranis configuration, the interactions between the exhaust jet and the airframe required careful assessment and evaluation. A dedicated afterbody wind-tunnel model was tested to quantify the effects of the jet on the aircraft’s overall stability and control characteristics and to provide throttle-dependent stability and control data.
Keeping high-tech affordable
The full paper is in the August edition of The Aeronautical Journal.
However, the biggest challenge faced by Taranis was to make the project affordable. Decisions were made early on in the programme with the specific intention of minimising programme cost. Those included a careful selection of the flight envelope with the aim of achieving primary demonstration objectives while avoiding regions of high risk and high complexity, using experience gained from previous demonstrators, minimising the wind-tunnel test programme and making maximum use of modelling and simulation. The maximum number of people working in the aerodynamics team was also limited to 12, including those devoted to flight control laws and air data.
Lee concludes by looking at how the experience of working on the Taranis demonstrator could be used not only for developing future aircraft designs but also how the streamlined process could reduce costs and the timescales of developing projects from concept to operational systems.
Existing subscribers to The Aeronautical Journal can access the full paper here. Non-subscribers can purchase a PDF of the paper by contacting the National Aerospace Library (E: firstname.lastname@example.org, T: 44 (0)1252 701038 or 701060).
Abstracts of all Journal papers published since 2003 are available online. Click here to browse by date or by subject.