Changing the shape of wing design using "digital materials"

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In the team’s new approach, the whole shape of the wing can be changed, and twisted uniformly along its length(Credit: Kenneth Cheung/NASA)

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A team from MIT and NASA led by Neil Gershenfeld is developing a new type of "morphing" wing that rather than using conventional flaps, changes its shape. This new wing is made up of overlapping strips that could be assembled by small robots, resulting in aircraft that are simpler to build, use less fuel, and boast improved agility.

Though we're used to airplane wings with moving flaps that control the craft's movements, the first flying machine built by the Wright brothers in 1908 used a different technique called wing warping. Instead of tilting airfoils attached to the trailing edges of wings, warping uses wires and pulleys to alter the shape of wood and canvas wings to perform the function that ailerons and flaps do in modern airplanes.

According to the NASA/MIT team, there have been numerous attempts to revive this technology, but these have relied on mechanisms inside the wing to bend it. The problem has been that this machinery usually turns out to be too heavy and complicated, which offsets any increases in aerodynamic efficiency.

The NASA/MIT approach is to not just do away with the internal mechanism, but to fundamentally redesign the structure of the wing so it is capable of bending by itself. Thedesign achieves this by dividing the wing into lightweight, overlapping scale- or feather-like sub-segments. These are supported by tunable and actively deformable modular building blocks, dubbed "digital materials," that are made of carbon fiber-reinforced polymers that can be quickly engineered and snapped together and allow the wing to deform while maintaining a smooth, aerodynamic surface.

This modular approach would allow the individual support pieces to be mass produced and combined in an almost endless variety of shapes, which could be constructed by simple minature robots that crawl along the exterior or even the interior of the structure as it is constructed. Though the researchers have already developed prototype robots, they built the initial test structure by hand and used skin panels instead of scales that would be used the ultimate version.

The units used were morphed manually using two small motors to twist the wingtips and bend the wing uniformly along its entire length. The purpose of this test piece was to get the wing to twist in the same manner as if it was made of separate scales instead of panels by fine-tuning the structure so it twists on command into the desired aerodynamic shape.

So far, wind tunnel tests have shown the test wing has aerodynamic properties of a conventional wing weighing 10 times more. The team then built a drone aircraft flown from the ground by a certified test pilot, who found it responsive enough to do aerobatics.

Gershenfeld sees this technology as not only leading to super-efficient long-range drones, but as having applications beyond aerospace engineering, inlcuding in wind turbines, skyscrapers, bridges, and space structures. It could also be used to create soft robots that can bend wherever desired without joints, are lighter than equivalent robots, yet can maintain the desired level of stiffness for the job. Repairs of machines built with the units would be cheaper and easier as damaged units could be replaced by maintenance robots with new ones.

The team's results were published in Soft Robotics.

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