Nanotube-based skins make morphing wing technology soar

- Ottawa, Ontario

Shapeshifting aircraft wings take inspiration from birds and bats

Looking out the window of a passenger plane at its wings, you will see flaps on the front and rear edges that extend and retract during takeoff and landing. As the front edge flaps move, they reshape the wings to increase lift during takeoff and open gaps for air flow. As it flows through the gaps, the air produces noise that can be heard around the airport and in nearby neighbourhoods. It is also turbulent, so it increases drag on the wings and requires more fuel to help power a plane forward.

Commercial airlines worldwide consume an estimated 370 billion litres of fuel a year, and air travel accounts for about 2% of global CO2 emissions annually. As passenger demand continues to rise and air-freight traffic surges, noise and greenhouse gas emissions (GHGs) will only increase.

Fortunately, a solution is in the works that eliminates the gaps in flaps, reduces noise during plane operations, improves aerodynamic performance, and guarantees less fuel consumption. Called a morphing wing, this innovation can bend, flex and stretch in response to real-time conditions, much like the wings of bats and birds. Morphing wings are covered by skins that, like overlapping scales and feathers, expand and contract during an aircraft's operation. This means that the skin needs to be both elastic and load bearing.

"The aerospace community is extremely interested in aircraft morphing technologies and related structures," says Wajid Chishty, Program Leader at the NRC's Aerospace Research Centre. "However, one of today's major challenges is the lack of suitable materials for making stretchable skins essential to the development of morphing wings."

But a collaboration between the Aerospace Research Centre and the NRC's Security and Disruptive Technologies Research Centre is expected to change the game.

More than skin deep

Michael Jakubinek, a research officer with the Security and Disruptive Technologies Research Centre, has co-invented a nanocomposite that can be adapted to the morphing wing skin.

Over the past few years, Jakubinek and his research centre colleagues along with those from aerospace had developed fabric-like sheets of carbon with a stretchable polyurethane. "The properties of this nanocomposite can be tailored so it is stiffer than an elastic, yet can still be stretched reversibly," he says. "This is the kind of combination needed for a morphing wing skin." He emphasizes that without the aerospace collaboration, he would not have thought to apply the material to a morphing wing. "Together, we identified the opportunity to connect the development of this novel material to an important challenge in the aerospace sector."

To be applied as a stretchable skin, the nanotube-based sheets are laminated around a layer of polyurethane and combined with an extendable substructure to support the skin. The teams from both these NRC research centres also used finite element modelling and 3D printing to design and fabricate various support structures. The skin, 3D-printed substructure and custom movement mechanism were combined to produce a 25-centimetre-wide, 2-metre long model wing where the front edge stretches by up to 20% as it morphs from a take-off to a cruise configuration.

"With a team covering everything from aerodynamics and design to materials and manufacturing, we built a technology demonstrator that addresses the most difficult aspects of this challenge," adds Chishty. "We believe that by tackling the toughest obstacles, we can ensure that our findings have a lasting impact on the industry."

Soaring into the future

The demonstrator marks a milestone in a lengthy research and development process that will continue with industry and government partnerships. One new direction, for example, is applying the technology to the wing tip. "This is an add-on retrofit so you don't have to change the whole wing," says Jakubinek. Another option is to test it on unmanned vehicles or in non-aerospace applications.

If wing-morphing technologies are adopted widely, the benefits can be substantial. In addition to eliminating most of the noise generated by wing operation, they could reduce airplane fuel consumption by more than 10%. This translates into a reduction in GHGs of nearly 90 million tonnes annually for the commercial aviation sector alone. The technology's multi-functionality, light weight, and adaptability to various conditions on the fly also make it a candidate for future aircraft configurations.

The bottom line: morphing wing technology is taking flight.

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