|Georgia Institute of Technology, www.gatech.edu|
Researchers at the Georgia Institute of Technology are developing cruise-efficient, short takeoff and landing (CESTOL) jet aircraft that could use relatively short runways.
The key to the design is the circulation-control wing, also called a blown wing. These wings have high-speed jets of air directed over their upper surface during takeoffs and landings to add lift. This yields several benefits, including steep climb-outs and approach angles. It also lowers drag at cruising speeds for better fuel efficiency, simplifies the wing shape, and lets smaller wings be more efficient at cruising speeds.
To create their CESTOL design, researchers placed turbofan engines above the wing rather than below as on most commercial airliners. This sends air over the wing for lift without impeding thrust for takeoff and high-speed flight. The design also cuts noise. The engine placement let the design team use a wing with only one relatively simple flap for added lift at slow speeds. The flap, however, is coupled with a circulation-control device. It consists of a narrow slot just above the flap and running along the entire length of the wing’s trailing edge. When the flap rotates downward on takeoffs and landings, it extends the chord of the wing and adds more curvature. Meanwhile, compressed air sent through the slot at these times increases the air velocity over the top of the wing and deflects the ambient windstream downwards so it curls under the wing. The result is two to four times the lift created by a conventional flap.
The Georgia Tech design also exploits interactions between air from the wing slots and engine exhaust. During takeoff and landing, air blowing out of the slots entrains the exhaust, pulling it down onto the wing and adding even more lift.
“These strategies let an aircraft fly at low speeds while the wing is experiencing much higher relative wind speeds on its curved upper surface due to this blowing and thrust entraining,” says principal researcher Robert Engler. “We have measured lift coefficients between eight and 10 on these pneumatic powered-lift wings at level flight conditions. The normal lift coefficient on a conventional wing at similar flight conditions is less than one.”