An unmanned X-Plane will test the boundaries of shape-shifting wings that counter a potentially deadly aerodynamic force. By Steve Rousseau
The Pentagon’s newest experimental military aircraft isn’t designed to evade radar or drop bombs; it’s an unmanned science platform that could make high-altitude, long-endurance air travel safer. Air Force Research Laboratory (AFRL) engineers will use the X-56A to look at an aerodynamic phenomenon known as flutter – dangerous vibrations in an aircraft’s wings.
To counter flutter, engineers typically thicken structural reinforcements such as spars and ribs. But this increases weight, which in turn eats up fuel. “We have a better approach,” says AFRL project manager Pete Flick. Instead of stiffer wings, the X-56A will test active flutter control, a system of sensors and flaps that detect and deflect increasing aerodynamic loads. Aircraft with active flutter control will be much lighter and so could potentially fly faster and more efficiently, Flick says.
Wing flutter is a phenomenon similar to what makes a flag flap. Vibrations caused by air passing over the wing can cause it to wobble or even snap in a matter of seconds. At a certain airspeed, at a certain altitude, the wings of any aircraft may start to become unstable. These limitations are part of what test pilots use to define an aircraft’s flight envelope – the conditions to which pilots must adhere to operate an aircraft safely.
Flutter is more severe at lower altitudes because the air is more dense. Therefore, X-56A researchers will conduct flight tests at higher altitudes to ensure the aircraft can adapt to the conditions before flying closer to the ground.