There are always smarter ways to make things, and these days there are usually also ways to make things smarter. EU-funded researchers have looked at aircraft structures from this perspective. In addition to innovative materials, they are proposing technology that would give airliners self-sensing capabilities and enable them to change the shape of their wings.
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The Saristu project set out to make aircraft structures cleverer and more cleverly, as a way to reduce weight, cut costs and enhance aerodynamic performance — thereby also saving energy. It delivered concepts for innovative carbon fibre panels and automatic damage detection, and advanced the development of morphing wings.
“We considered three levels of intelligence,” says project coordinator Piet-Christof Wölcken of Airbus Operations in Bremen, Germany. The basic level, he explains, is passive: intelligence applied in the making of an object that may, as such, not be particularly brilliant.
One level up, he notes, some degree of self-awareness is required. “The aircraft structure must become savvy to its own status,” Wölcken remarks. “Our aim was to develop a self-sensing system.”
And, as a next step, the team argued that the structure could be equipped to react to information from its sensors. “So, as a third building block, we looked into structures that can change their shape,” Wölcken reports.
An electric idea
Saristu’s quest for new bright ways of making things focused on carbon-fibre-reinforced polymer (CFRP), a composite material used in the structure of various planes. These advanced composite materials offer a number of benefits compared to metals.
However, they don’t conduct electricity well, which is a major drawback as various key functions rely on this property, Wölcken explains. The structure of the plane is used to earth the electrical systems on board, for example. Current solutions to this problem usually involve adding materials that increase the weight, partly cancelling out a key advantage of using lightweight composites, he notes. They also raise the installation costs.
Saristu, he reports, has found a way to endow the material itself with the required conductivity and demonstrated this property in prototypes of various complex parts. This advance, which is based on a sophisticated use of nanoparticles, could take CFRP a step closer to realising its full potential in aviation.
How are we today?
With its self-sensing system, Saristu aims towards reducing the need for unscheduled inspections. Sometimes, says Wölcken, experts have to be called in unexpectedly to check for possible damage to a plane — for example, if there is an incident during ground handling, such as a catering truck bumping into a plane. An inspection would be required to ensure that the structure is still sound, a specialist might have to be flown in to perform it, and the process itself takes time.
Such delays can have significant implications for airlines, both financially and in terms of customer satisfaction, but the system proposed by Saristu could help to pre-empt many such situations. Sensors embedded in the structure would enable the plane to check its status instantly, Wölcken explains, and actual inspections would only be needed if the system detects cause for concern.
The shape of wings to come
Self-sensing also feeds into Saristu’s work on shape-shifting structures. It would be very useful if aircraft wings could adjust their contours to optimise aerodynamic performance, and a lot of brainpower has been invested worldwide to develop such technology. “But the requirements are so tough that to date we don’t have any morphing structures flying in commercial aircraft,” Wölcken explains.
The project refined and tested approaches formulated by earlier research, and combined these in a demonstrator of a morphing wing. It also developed a “skin” material able to deform with the structure without creating folds or gaps, says Wölcken.
Saristu ended in August 2015, having taken exciting concepts closer to possible deployment. Many of its consortium members have joined forces in a bid to launch a follow-on project that would build on its outcomes.
Pilot lines for the production of Saristu’s conductive composite panels are already being designed in another EU-funded project, named Platform. Among the innovations advanced by Wölcken and his crew, this one might therefore be the first to fly.