Shapeshifting metals could greatly improve aircraft efficiency
Constructing aeroplane wings from metal that changes its shape could significantly improve the efficiency of flights. Airline industry engineers are examining the potential for replacing the heavy hydraulics and mechanical parts needed to move wing flaps with what is known as shape memory alloys. These would be up to 90% smaller and lighter than existing parts, helping to save on weight and fuel costs. The metals can be made to change their shape by subjecting them to changes in temperature, but technical problems of controlling the effect remain, given the extreme changes in temperature that take place in flight.

Humanity may be divided on a great many issues, but most would agree that it would be very cool to have airplane wings made of shapeshifting metal. The geometry of those fabulous foils affects virtually every aspect of flight, and making them from metal that can change its shape in midair could make your journey smoother, safer, and more efficient.

Shapeshifting wings aren't new. The Wright brothers flew over the North Carolina sand dunes using a hip brace and wires to warp the Flyer’s cloth-and-wood wings. Modern aircraft achieve the same results—OK, much better results—with mechanically driven flaps, slats, ailerons, spoilers, elevators, and rudders.

“If you look at conventional aircraft technology, you have so many moving parts,” says Othmane Benafan, an engineer at NASA's Glenn Research Center. Those moving parts are essential—they are how pilots steer, reduce turbulence, take off, land, and basically do everything else besides glide aimlessly. But the actuators, cables, motors, lubricant, hydraulic gear, and other bits needed move those parts around take up weight and space—precious resources on any aircraft.

The alternative is to move those wing parts using shapeshifting metals. Or, as they’re known to engineers, shape memory alloys. “Parts made from shape memory alloys are typically 10 to 20 percent the size and weight of a conventional part,” says Jim Mabe, a shape memory alloy guru at Boeing. For an industry that spent $133 billion on fuel last year, anything smaller and lighter is exciting news.

Shape memory alloys are essentially reversible Shrinky Dinks. When heated to certain temperatures, they shrink, twist, and bend. Cool them off, and they return to their original shape. Hot, cold, hot—shape memory alloys can cycle back and forth millions of times without wearing out. All you need is the ability to generate heat or pull it from some other, already spicy hot part of the plane, like the engine.

Aircraft makers, researchers, and government agencies like NASA can use these metals to do more than just reduce fuel bills. Shape memory alloys can also be used to add moving parts to a plane, doing things that would cost too much in size and weight using conventional mechanics. For instance, quieting a jet engine's roar. Temperature activated fold-up wings would allow aircraft carriers to cram more fighters on deck. This tech might even quell sonic booms, opening the door to the revival of supersonic passenger jets like the Concorde.

Down Shape Memory Lane

Shape memory alloys were developed in the aerospace field, though not for flight, per se. In 1959, at the Naval Ordnance1 Laboratory, a researcher named William Buehler was developing materials for intercontinental ballistic missile nose cones that could endure the extreme temperatures and pressures of doing missile stuff like flying to the edge of space, then reentering the atmosphere. Buehler came up with an alloy of nickel and titanium that was not only strong and fatigue resistant but also super malleable at high temperatures. He discovered the alloy’s most surprising feature by purposely dropping bars of the stuff on his shop floor and listening to the thuds. (I know, these are the kinds of stories people should be telling STEM-shy kids.)

The cool bars made a very different noise than the bars still warm from the furnace, indicating to Buehler that the molecules could be in different orientations at different temperatures—not a common property of metals. Later one of his colleagues held his lighter under an accordion-like strip of the alloy. To everyone’s surprise it completely unfolded, indicating that the heated molecules were doing more than just expanding in response to the heat; they were completely changing the orientation of their bonds. These alloys change phase, but not from, say, solid to liquid. They’re changing from one solid phase to another—like ice turning into a different kind of ice.