Electrically-powered passenger aircraft? Intelligent paint? Planet-exploring micro robots? BILL READ looks into the science of nanotechnology and the remarkable changes that such research could offer to change the future of aerospace. This is a full article published in Aerospace International: October 2011

 
[caption id="attachment_5593" align="alignnone" width="290" caption="Nanotechnology could have important applications in aerospace."][/caption] 'What mighty oaks from little acorns grow?' Popular proverb Think of an object one metre long. Now divide it lengthways into one billion pieces, each measuring 0.000000001 of a metre. That is a nanometre (nm), a unit of length equivalent to the diameter of a helium atom. Or — to give a relative dimension — the size of a nanometre compared to a metre is the same as that of a marble relative to the Earth. Over the past 30 years, the introduction of new technology such as the atomic force microscope (AFM) has enabled scientists to both study and manipulate matter at the atomic level, a innovation that has led to the development of nanotechnology, the science of manipulating structures of between 1nm-100nm in at least one dimension. At first glance, such quantum-size science might appear to have little relevance to aircraft. However, nanotechology applications are starting to be used in an ever increasing number of scientific and commercial applications, including medicine, electronics, biomaterials, energy — and  aerospace. For example, nanotechnology can enhance the mechanical properties of metal, composite and metal-composite blends used in aerospace construction. Such tailored materials can exhibit lighter and stronger properties than their conventionally manufactured counterparts -an obvious advantage to aircraft and aircraft component manufacturers trying to produce aircraft which are more efficient and economical to operate.  

Moving atoms

The microstructure of a typical aerospace aluminum alloy viewed through an electron microscope reveals that the arrangement of atoms is far from perfect. These imperfections, such as dislocations, grain boundaries, and voids, can all contribute to weak mechanical properties. It has been demonstrated analytically that the theoretical strength of such an alloy could be up to 100 times greater than the actual value measured in a mechanical testing lab. However, using an AFM, it is possible to remove and reposition individual atoms to remove such defects. Nanomaterials can be produced in two different ways — ‘bottom-up’ in which structures are created using nano components and ‘top-down’ in which existing materials are transformed so that they have new properties. Bottom-up methods, which include inert gas condensation, consolidation of nanopowders, electro dispositions or crystallization from an amophous state, can currently only produce very small items with dimensions of only a few millimetres. The top-down approach uses a process known as severe plastic deformation (SPD) which can transform metals or alloys with conventional grain size into bulk materials with a submicron or nanoscale structure. Nanostructured materials can also be manufactured with smaller grains which have enhanced strength, hardness and corrosion resistance. There are a variety of nanoscale materials but the one that has received the most attention have been carbon nanotubes (CNTs) which have a shape equivalent to a two-dimensional sheet rolled up into a tubular structure. Such nano structures can been assembled into a concentric set of cylinders, known as a multiwalled carbon nanotube (MWCNT). CNTs have attracted the interest of engineers because they exhibit extraordinary mechanical properties. Not only do these have very high tensile strengths (one estimate claims they have a stiffness ten times that of diamonds) but they also exhibit high thermal and electrical conductivity. To take advantage of these qualities, nanotechnology researchers are experimenting with hybrid materials created by embedding nanoparticles into the matrix of a polymer. By using CNTs as reinforcing agents, materials can produced which are not only lighter and stronger but also have enhanced abilities to resist vibration and fire. Polymers can also be created which have antistatic properties and electrical conductivity.  

Work in progress

[caption id="attachment_5602" align="alignnone" width="330" caption="Much work still needs to be done."][/caption] However, there are still a number of problems to be overcome. Such hybrid materials will only be as strong as the strength of bonds holding the particles together. Up to the present, it has proved very difficult to find a way to disperse the nanotubes homogeneously across the host matrix. There is still much to be done in this area and research is being carried out, together with the development of enhanced modelling techniques. to try and better understand the interface between nano, micro and macroscale regions and its effect on structural and mechanical properties Currently, such nanomaterials are still very expensive to create and can only be produced in small quantities. CNTs are relatively expensive to produce and manipulate and are short in length which makes then unsuitable for replacing larger aerospace components. There are also risks associated with smaller grain nanomaterials in that the grain size should not be made too small or the material may begin to suffer from brittleness.  

Aerospace applications

[caption id="attachment_5599" align="alignnone" width="403" caption="In February this year, UK low-cost carrier EasyJet announced that it was the first airline to trial a new nanotechnology ultra-thin coating on its aircraft which it predicted would reduce its fuel consumption by 1-2%. EasyJet is testing the coating on eight aircraft over a 12 month period. (easyJet)"][/caption] Despite these initial setbacks, the long term benefits for aerospace are worth striving for. By using nanomaterials, researchers have predicted that aircraft of the future could weigh only half as much as their current counterparts — offering huge potential savings in both fuel costs for airlines and reduced carbon emissions. As well as being lighter, nanomaterial aircraft would also have the additional benefits of being stronger and more flexible and thus more resistant to impact. While there is still a long way to go before nanomaterials are used in large scale applications on aircraft, research is currently under way into a number of areas where nanomaterials could be applied to aerospace. In recent years, commercial aircraft manufacturers have been making increasing use of composite materials in aircraft construction. Composites have the advantage of being lighter and stronger than many aluminium alloys but also may contain inbuilt defects created in the manufacturing process. While more resistant to impacts, damage is more difficult to detect and repair than metal components. Composites also have poor electrical conductivity and are thus are thus more at risk from lightning strikes. The properties of composites over time is also not yet fully understood, such as degradation due to exposure from ultraviolet rays and delamination caused by impacts, moisture or excessive strains. Stronger nano-reinforced composites could, potentially, avoid many of these problems. Some work has already been done in this direction. New aircraft component materials, such as GLARE (glass laminate aluminium reinforced epoxy) — a new laminate material made of aluminium and glass fibres which is used on parts of the Airbus A380, could be made even stronger by enhanced the bonding between the metallic and fibre sheets with nanoparticles. Nanostructured metals are ideal for certain aircraft components where additional strength is required, such as the front or tail of an aircraft which might be at risk from bird strikes, areas around windows and doors, sections of the fuselage which is under stress and the undercarriage. One project is looking at fatigue crack growth retarders for aircraft construction using undirectional carbon fibre reinforced epoxy straps while another has focused on new fire-resistant panel materials for use in aircraft bulkhead and structural flooring. Another area where nanomaterials could make a difference is in aircraft maintenance. Aircraft are subject to stresses and strains during flight which can cause cracks to develop. Accordingly, structures need to be inspected and repaired on a regular basis — a process that costs airlines both time and money. The development of nanomaterials with enhanced mechanical and fracture resistant properties could greatly reduced this cost.  

The electric effect

[caption id="attachment_5601" align="alignnone" width="250" caption="Nanotechnology could radically reduce the size and weight of aircraft sensors. (Honeywell))"][/caption] Other nano applications include the development of components with enhanced electrical and thermal conductivity which could be used in aero engines, low-wear resistance aircraft brakes, ‘smart’ electro chromic glass aircraft windows that can lighten or darken, LEDS for aircraft lighting, and the replacement of copper wiring with lighter polymer wiring made of electrically conductive carbon nanofibres. Nanotechnology is also being applied to develop improved electronics with low power consumption, new sensors and multi-functional materials with embedded sensors. Researchers see potential in the application of such equipment to aircraft to create small low-power consumption sensors that can perform at high temperatures together with other physical and chemical sensors that can perform safety inspections quickly, more efficiently and more cost effectively than present procedures. Applications could include micro gyroscopes, paint that could act as an aircraft structural health monitoring system and nanosensors that could detect the presence of fires, biological or toxic chemicals in aircraft holds. Another nano research area which could have an radical effect on the aerospace industry is the development of low-cost, low-mass electrical storage devices. Nanotechnology is already being used as part of in-flight entertainment systems on aircraft but is also reducing the size and weight of supercapacitors that provide power for motors for electrically-powered aircraft. Recently, the introduction ofgreatly  improved electric batteries and engines has enabled the development of small electrically-powered aircraft. While the use of electric power is currently only practical for  powered gliders and light aircraft, analysts predict that advances in nanotechnology could eventually result in the development of superconductive materials that could be used to power passenger-carrying airliners. Another nano application of relevance to aerospace is the development of new fuel additivies. Both liquid and solid fuels can be improved by the addition of nano-sized energetic particles which will allow high combustion temperatures, faster energy release rates, shorter ignition delay, more complete combustion and rapid energy release. Additional nano applications include the developement of wear-resistant tires together with active noise control techniques, improved avionics, communication and radar technologies.  

Protective coatings

One nanotechnology area that is already reaping benefits for the aerospace industry has been in the development of coatings which can be applied to protect other materials. Unlike aircraft components, coatings do not need to be produced in large scale sizes. Already, research on material properties on the nanoscale has enabled the development of new high durability and performance thermal barrier coatings for gas turbine engines which can insulate superalloy turbine blades and vanes from hot gases. Such coatings are both erosion-resistant and have low thermal conductivity. It has been estimated that the application of high temperature nanoscale materials could lead to an increase of the thrust-to-weight ratio of up to 50% with fuel savings on conventional engines of 25%. Very hard coatings resistant to corrosion have also been developed can be used to protect assembles such as landing gear. In fact, the potential for nano-enhanced coatings for aerospace is proving to quite extensive with research being carried out into a wide variety of applications. These include corrosion-resistant coatings, aircraft paints that are more durable, heat-resistant, smoother and scratch resistant, self-cleaning and self-healing coatings, anti-bacterial coatings for aircraft interiors, hard compound ceramic films for propeller blades and even electrically conductive coatings which could be heated to aid aircraft de-icing.  

Out of this world

[caption id="attachment_5598" align="alignnone" width="250" caption="NASA's nanotechnology 12-TET Rover is designed to cope with any terrain. (NASA)"][/caption] Nanotechnology applications are not just limited to aircraft. Because of the high cost of launches, the space industry is particularly interested in the development of new lighter materials. CNT-based components could also be used to replace silicon-based devices which are vunerable to proton radiation. The Materials and Coatings Laboratory at the French CNES (Centre National d’Etudes Spatiales) space agency has looked at how polysiloxane coatings can protect satellites from thermal variations in orbit, as well as preventing electrostatic discharges. US researchers at the University of Dayton and the Air Force Research Laboratory are investigating the potential of ‘shape-memory’ polymers that can be be folded and spring back into shape when heated — which could be used to create structures that are stored in a small space during launch and then unfurled in space. Research into space nanotech applications is also looking at the development of materials that are radiation resistant, together with more efficient ways to generate and store energy, such as solar and fuel cells, batteries, accumulators and capacitors. Nanotechnology could also lead to more high performance computing power for faster processing of satellite data. Other space nano research areas include the development of gossasser thin materials for space sails and the development of filaments light and strong enough to be used for space elevators which could be used to haul people and goods from Earth up into orbit. Thinking even further away from Earth, scientists predict that nanomaterials could be used to build autonomous reconfigurable ‘thinking’ spacecraft. A new generation of miniature space craft could be created, including micro spacecraft for monitoring and measurements, networks of ultra small probes to explore planetary surfaces and even micro-rovers that could drive, hop, fly or burrow. One example of this is the NASA 12-TET?Rover being devleoped by NASA?Goddard Space Center as part of its Autonomous NanoTechnology Swarm (ANTS) project. Comprised of 12 tetrahedrons made of 26 struts the autonomous 12-TET?Rover is designed to be able roam all the different terrains of Mars.  

Encouraging research

Inspired by the potential benefits that nanotechnology might bring, a number of projects have been set up by governments and organisaitons to encourage nano research. In Europe, the European Commission (EC) has included nanotechology in its funded research programmes. One project in the Fifth EU?Framework Programme (FP5) was the setting up of Nanoforum — an EC-funded international network of organisations conducting nanotechnology research which organises conferences and meetings, as well as producing annual reports and specialist publications. As part of its portfolio of 6th EU Framework (FP6) Projects, the European Union published a report on potential industrial nanotechnology applications called NanoRoadSME which set up a roadmap up to 2015 of potential nanomaterial industrial applications that could be adopted by small and medium enterprises (SMEs). An EU report on the state of nanotechology published in 2011 reported that much work still needed to be done to tackle the problem of how to produce bigger, good quality nanocomposite and nanostructured metals parts for the transport industry on an industrial scale. However, the use of nanocoatings in engines was already realising cost benefits. The EC has just published a call for new nanotechnology projects to be considered for inclusion FP7 in 2012, convering a wide variety of disciplines, including transport. In addition to the EC, the US, Japan and China have also been conducting much research into nanomaterials. NASA has published a number of reports, including a Nanotechnology Roadmap in 2010 showing its potential applications on future space missions. In 2007 Airbus published the result of VIVACE, a €70m project conducted with 50 other partners at the Mitre Corporation’s Centre for Advanced Aviation System Development (CAASD). The aim of the VIVACE (Virtual Aeronautical Collaborative Enterprise) consortium was to integrate supplies chains and reduce development times and operating costs. The research encompassed a number of nanotechnology projects, including nano-reinforcement of composite materials, self-healing metal polymer matrix components and nanocomposite materials for A380 air conditioning system sliding bearing valves. Work has also been conducted into self-healing intermetallic alloys and composites. Nanotechnology research is also being assisted by groups such as CANEUS — an international non-profit organisation which encourages the development of micro nano technologies) MNT to cater to the needs of the aerospace community. CANEUS offers help with funding ‘pre-seed’ projects to creation of ‘blueprints’ for MNT aerospace pilot projects which can then be developed from concept to prototypes. CANEUS holds a series of conferences on nano-related subjects.  

Still at the acorn stage

[caption id="attachment_5600" align="alignnone" width="403" caption="Artist’s concept of EADS’ Voltair large all-electric aircraft design presented at the 2011 Paris Show Show — a design that nanotechnology could make possible. (EADS)."][/caption] So when are all the marvellous nano-structured creations going to start appearing? Some, such as the protective coatings mentioned earlier, are already being introduced, as is technology used in other applications as well as aerospace, such as electronics or micro processing. Radically different future designs, such as a super-strong, lightweight, electrically-powered passenger aircraft may take a little longer to develop. Before such products can be realised, much research still needs to be done into creating nanostructures that are strong and reliable to use over time. Nanomaterials are still a long way from industrial scale processing and new methods need to be developed to produce nano-enhanced structures in larger sizes and more cheaply. The adoption of new nanomaterials into aerospace applications is also being limited by the time required for certification by competent authorities to ensure that parts are safe for use in aircraft. The progress of nanotechnology in space applications is also being slowed because of the difficultly of testing the actual effects of being in space. In situations where components cannot be tested in practice, more efficient modelling tools are being developed to at least test them in theory. To conclude, nanotechnology is still very much at the beginning of its development cycle and it is not yet possible to accurately predict where it will end. Certainly, nano research will impact a wide range of different industries and disciplines, possibly in quite radical ways. There are still many aspects of nanotechnology still under scrutiny, including how such tiny particles might impact human health, but the results could be truly game-changing.  

Aerospace International Contents - October 2011

News Roundup - p4 Aerospace: the Gloabl Challenges - p12 Overview of current aerospace issues Russia resurgent?- p 16 Show report from MAKS 2011 The 787 awakes - p18 How airlines are getting ready for the 787 The new European space age p 22 Analysis of Europe's growing space sector Think big, think small - p 26 What benefits could nanotechnology bring to aerospace? Drones of peace - p 30 The UK's ASTRAEA civil UAS initiative The last word - p34 Keith Hayward looks at the globalisation and consolidation of airlines
  This is a full article published in Aerospace International: October 2011. As a member, you recieve two new Royal Aeronautical Society publications each month - find out more about membership.

Bill Read
14 October 2011