Air Force

Variable camber compliant wing

Morphing the shape of a wing in flight broadens the mission capability of an aircraft, creates energy efficiencies, and reduces noise

Other

In the early years of manned flight, wing warping was used for lateral control of an aircraft. This technique, used by the Wright brothers, consisted of a system of pulleys and cables, used to twist the trailing edges of the wings in opposite directions.

Because most wing warping designs involved flexing of structural members, they were difficult to control, and the risk of structural failure was high. As aircraft further developed, wing warping was replaced by multiple, independent, rigid flight control surfaces, such as ailerons, leading edge slats, and flaps and while this approach is still in use, it is not without problems.

AFRL Variable Camber Compliant Wing Prototype (1 ft span, 2 ft cord) (a) Undeformed wing geometry (b) Deformed (6% camber change) (c) Twist (d) Deformed (rear view)

The control surfaces create drag during use, which can result in unnecessary fuel consumption. There are also inherent gaps formed between the control surfaces and the wing structure that generate noise. Finally, fixed, independent control surfaces limit the variation in wing shape and thus the overall utility of an aircraft.

To advance aircraft capabilities, the Air Force Research Laboratory has developed a novel adaptive variable camber compliant wing (VCCW) that can re-contour the airfoil camber in-flight. These are flexible, often single piece structures that change shape through elastic deformation. This distributed camber control enables a continuous wing reconfiguration that optimizes wing geometry for current altitude, airspeed, and lift-to-drag ratio requirements. The VCCW also limits separated flow and parasitic drag with the seamless construction (no holes or gaps), which increases overall range and endurance of an aircraft in addition to controlling surface effectiveness and power use reductions. The wing reconfiguration also decreases aircraft noise, e.g., the flap side-edge noise, and with a seamless skin reduces control surface gap and edge noise.

Notably, the wing skin is not required to be stretchable or to slide over the ribs to change camber because bending of the ribs is the main deformation mode of the mechanism. This trait is desirable for manufacturing and energy perspectives since the attachment of the skin is simplified, and the bending of the skin with the ribs requires less actuation energy than a surface that stretches. The skin may also be constructed from a single piece of material such as a metal sheet, glass fiber, composite material, or other thin bendable material.

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