When we look out of the window as our aircraft comes in to land, we are used to seeing flaps and slats deploy, and slots open, as the wing reconfigures to increase lift and reduce landing speed. But, in the cruise, not much happens to the wing except small movements by individual control surfaces as the aircraft maneuvers or responds to turbulence.
All graphics: Boeing/NASA
Now Boeing and NASA are working on the Variable Camber Continuous Trailing Edge Flap (VCCTEF) system (graphic above), which would smoothly change the wing’s shape continuously throughout the flight. By continuously varying camber, the VCCTEF would provide efficient high lift for takeoff and landing and reduced cruise drag through active control of the twist of a flexible wing.
There are 42 flap sections on each outboard-wing trailing edge (see above), each commanded individually to change wing twist as aircraft weight and cruise conditions change. In place of conventional flaps and ailerons, the outboard wing has 14 “tri-flap” sections, each 24-in wide with an 8-in flexible fillet between them, providing a continuous trailing edge. Each tri-flap has three chordwise segments, actuated at their hinges to vary the flap’s camber.
In cruise mode, the VCCTEF controls wing twist to optimize lift-to-drag ratio. Deflection is limited to a 2° differential between sections by the flexible strip. For landing, all the outboard tri-flaps are deflected 45° down and conventional three-section inboard flaps deployed to provide full-span high-lift devices (see below).
In the absence of conventional ailerons, roll control is accomplished by differential deflection of the tri-flap trailing segments across the full span. The inner two segments of each tri-flap have shape-memory alloy actuators, which are light, but slow. The trailing flap segment has a heavier but fast-acting electric rotary actuator, allowing it to act as an aileron.
Work on the VCCTEF concept is part of NASA’s research into flexible low-drag, high aspect-ratio wings for aircraft that could enter service after 2025. NASA is aiming for structural weight reductions of 25% and aspect-ratio increases of 30-40% for cantilever wings.A small-scale wind-tunnel test of the flap system is planned this year at Washington State University, using a 6ft semi-span flexible wing model.