NASA has successfully applied a new technology that allows aircraft to fold their wings to different angles while in the air.
Previous attempts to do this were largely unsuccessful as they used heavy and bulky conventional motors and hydraulic systems. The Spanwise Adaptive Wing (SAW) project uses shape memory alloys built into an actuator on the aircraft, where it has the ability to fold the outer portion of an aircraft’s wings in flight without the strain of a heavy hydraulic system.
The alloy is triggered by temperature and works by using thermal memory in a tube to move and function as an actuator. Upon being heated, the alloy would activate a twisting motion in the tubes, which ultimately moves the wing’s outer portion up or down.
On subsonic aircraft such as commercial airliners, the potential aerodynamic benefits of folding the wings include increased controllability, which might result in reduced dependency on heavier parts of the aircraft, including the tail rudder. Additionally, pilots can take advantage of a number of different flight conditions, such as wind gusts, by folding the aircraft’s wings to adapt to any particular condition experienced in flight.
One of the most significant potential benefits of folding wings in flight, however, is with supersonic flight.
“There’s a lot of benefit in folding the wing tips downward to sort of ‘ride the wave’ in supersonic flight, including reduced drag. This may result in more efficient supersonic flight,” said SAW Principal Investigator Matt Moholt.
“Through this effort, we may be able to enable this element to the next generation of supersonic flight, to not only reduce drag but also increase performance, as you transition from subsonic to supersonic speeds.”
A series of flights at NASA’s Armstrong Flight Research Center in California demonstrated the material’s application and use on an autonomous flight testbed called Prototype-Technology Evaluation Research Aircraft (PTERA).
This aircraft was flown in a large “racetrack” pattern, providing long legs of flight in which the necessary manoeuvres for the research could be done. For the first two flights, the wing tips were rigged to fold downward, while later flights featured rearranging the hardware to achieve 70-degree upward deflection. Wing-folding manoeuvres were achieved in flight within three minutes each.