Across airframes and engines, and even interiors, the performance of civil airliners is being made safer and more efficient through the use of exotic new materials. Whether it’s the development of graphene-infused composites for fuselages, or the ‘growing’ of more heat-resistant single-crystal turbine blades, engineering magic at molecular level is promising an exciting future for flight.
Impressively, it is British-based organisations that are leading the way. Notable materials advances are being made at the top of the supply chain by aerospace giant Rolls-Royce, while small firms are working with academia to deliver collaborative research success.
“Mechanical and chemical engineers are working together to create some really clever composite and polymer materials,” says Helen Meese, head of engineering in society at the Institution of Mechanical Engineers. “Britain has a reputation for aerospace excellence, and it all bodes well for the future.”
Perhaps the most intriguing example of these material advances is the development of electrically conductive graphene-enhanced composites for aircraft bodies. Carbon-fibre composites are already used extensively in applications such as fuselages, leading edges and wing surfaces. However, because the carbon-fibre-reinforced epoxy composite materials are poor conductors of electricity they are prone to damage from lightning strikes. This has led to aircraft builders incorporating copper or aluminium meshes in the composite materials which add significant weight, and cost, through use of more fuel.
The electrical conductivity of graphene-enhanced composites has already been established. And the aim of the new project, involving Carmarthenshire-based Haydale Composite Solutions, along with Airbus UK and BAE Systems, is to develop highly electrically conductive epoxy resins through the addition of functionalised graphene. When combined with carbon fibre, these could result in a highly conductive carbon-fibre-reinforced epoxy composite material capable of withstanding lightning strikes. The development of such a material would result in safer aircraft, and lower weight and cost savings from the elimination of the expensive metallic meshes.
Haydale’s managing director Gerry Boyce says that the ability to add graphene to change one of the fundamental characteristics of the base resin – in this case electrical conductivity – is a hugely important development for engineers and could lead to a whole new generation of graphene-enhanced composite materials.
“There are major advantages in incorporating graphene in aircraft,” he says. “The principal way of using graphene will be to incorporate it into the resins used in the construction of the carbon-fibre-reinforced structures. Making the epoxy resin electrically and thermally conductive has potential positive implications on lightning strike protection and thereby can replace the need for a parasitic copper mesh which will save weight and cost.”
Taking on less water
“Also, by incorporating electrically conductive graphene, it is believed that composite materials could be used to de-ice aircraft. And it is believed that adding graphene will increase the materials’ hydrophobicity – reducing the amount of water absorbed by the composite which can save a lot of weight – as much as 2-3%. There are numerous other advantages including electromagnetic shielding and fatigue improvement.”
Boyce says that, while the potential of such materials is huge, there are still engineering hurdles that need to be overcome before they can enter service. “There are technology challenges around the identification of the right form of graphene materials, optimised functionalisation and concentration within the epoxy resins,” he says.
“There are also validation and certification costs and timescales to be considered, along with the development of technologies which don’t require moulding companies to change their production capabilities and processing equipment.”
Graphene-infused composites aren’t the only materials advances being studied by British researchers. A team of academics from the University of Bristol is looking at aircraft wings that can detect and repair small-scale damage to their structures. The research was started three years ago by Duncan Wass, professor of catalysis in the university’s school of chemistry, as an “on the back of an envelope” project. It has led to a usable technology that Wass thinks could be commercialised within a decade.
The self-fixing wing technology involves adding tiny, hollow ‘microspheres’ to carbon composite material – so small that they look like a powder to the human eye. If the wing is damaged, these microcapsules rupture and come into contact with a catalyst. A chemical reaction takes place which causes polymerisation to ‘glue’ together any cracks. Wass says his studies show that this can give up to 100% recovery of mechanical strength. The technique could only self-heal very small cracks which, if ignored, could eventually lead to catastrophic failure. In operation, the technique could be used to extend maintenance schedules or allow planemakers to use less composite material without compromising safety.
Inside aircraft cabins, meanwhile, materials advances promise potential weight and fuel-saving benefits to airlines. The advances stem from an eight-year campaign by Manchester-based Magnesium Elektron to make modern lightweight magnesium alloys available to aircraft seat designers and manufacturers. For many decades, magnesium has been banned from use in aircraft seats owing to concerns over flammability. But Magnesium Elektron has been working closely with the US Federal Aviation Administration (FAA) to prove that the latest alloys present no greater risk than widely used aluminium alloys.
After a long-running full-size fire test programme using magnesium seats fitted inside a fuselage, in August the FAA finally announced a new design standard recording the removal of the regulatory ban on the use of magnesium alloys in commercial aircraft seats.
“Our years of hard work have finally paid off,” says Bruce Gwynne, Magnesium Elektron vice-president of strategic development. “This new standard is a major landmark for the aircraft seating industry. Given the ongoing need to improve airliner fuel economy and reduce CO2 emissions, seat designers are now able to capitalise on the lightweight characteristics of our advanced Elektron magnesium alloys, which offer weight savings of between 15% and 20% over aluminium in an equivalent component that will meet all the strength and safety requirements for aerospace.”
Graham Wardlow, managing director of UK operations at Magnesium Elektron, sees other advantages of using magnesium inside the aircraft cabin. “We as engineers immediately think about weight and fuel savings when introducing new materials,”
he says. “But airline operators have their eyes on other benefits centred around passenger experience.
“For example, the seat tables that pull from arm-rests – they can be quite unwieldy. You could see how this might be made easier if the component was made from lightweight magnesium. Also, the cold, metallic feel of magnesium is superior to other alloys, and that excites airline interior designers who are trying to reflect luxury.
“Meanwhile, if magnesium has delivered as much as 15-20% weight saving over aluminium per component it has replaced, then interior designers could be allowed to put more comfort inside the cabin, or to improve the quality or nature of the in-flight infotainment system. And you can see how magnesium might provide weight advantages on equipment such as galley carts.”
Morphing materials
The efforts of Magnesium Elektron are likely to lead to magnesium entering service as part of aircraft seats in the relatively short-term future. But at other companies the thinking of engineers isn’t constrained by the mundanities of commercial reality. At Airbus, for instance, a blue-skies research team is given freedom to look at how new materials might impact aviation as far forward as 50 years’ time. The results are startling, with bionic and morphing materials coming to the fore.
A research paper issued by Airbus suggests that aircraft could be built using a bionic ‘airframe’ that mimics the bone structure of birds. Bone is light and strong because its porous interior carries tension only where necessary, leaving space elsewhere. By using bionic structures, says Airbus, the fuselage would have the strength it needs, leaving designers to make the most of extra space where required. This would not only reduce the aircraft’s weight and fuel burn, but also make it possible to add features such as oversized doors for easier boarding and panoramic windows.
Morphing materials that change shape and return to their initial form, growing like the leaves of a plant, are also a very real possibility, says Airbus. Such morphing materials might be metals or polymers that have a ‘memory’; or are covered with a ‘skin’ that will instigate a shape change. A memory is created using sensor and activator systems that give materials a level of artificial intelligence, allowing them to adapt to the passengers’ needs.
Another innovation would be to coat the cabin’s bionic structure with a biopolymer membrane, which would control the amount of natural light, humidity and temperature, providing opacity or transparency on command and eliminating the need for windows. This smarter structure would make the aircraft lighter and more fuel-efficient. It would also offer passengers unobstructed 360° views of the skies through the transparent walls of the cabin.
In focus: Graphene flies by drone
A collaboration between two North West universities has resulted in the first test flight of an unmanned aerial vehicle (UAV) partly built with graphene.
The test flight, carried out by the Engineering Innovation Centre at the University of Central Lancashire (UCLan), and the University of Manchester’s National Graphene Institute, took place in Preston. The flight sought to trial graphene on the wing of a UAV to test its robustness, aerodynamic properties and how it might be integrated into the manufacturing process of new aircraft.
Billy Beggs, UCLan’s innovation manager, says: “The demonstration was a world first, and our initial flight tests have been very encouraging. Graphene has huge potential for aerospace; it is incredibly strong, yet lightweight and flexible. Through our partnership with the National Graphene Institute, and Lancashire small firms, we aim to draw up a route map that enables graphene to play a key role in the development of the aviation industry.”
James Baker, business director at the National Graphene Institute, says: “This is the first demonstration of a UAV containing graphene components, in this case a graphene-coated wing. The aim is to investigate the potential effects of graphene in drag reduction, thermal management and ultimately the ability to achieve lightning strike protection.”