How easy is it to design a 737-sized jetliner that can land on a runway more suited to a turboprop - or a Cessna? Georgia Tech reserach Institute (GTRI) provides some insight in the latest issue of its Research Horizonsmagazine, which features its NASA-funded work on a cruise-effiicient short take-off and landing (CESTOL) aircraft.
Concept: Cal Poly
As part of a team, led by California Polytechnic State University (see previous post), working on NASA's four-year Hybrid Wing-Body Low-Noise ESTOL program, GTRI is leading the aerodynamic and acoustic design of a powered-lift aircraft. This includes building large-scale wind-tunnel models like this one:
NASA's CESTOL requirements center on the ability to take off or land in 3,000ft, yet cruise efficiently at Mach 0.8 and 30,000ft. GTRI's powered-lift design is a circulation-control wing, which combines blown flaps with upper-surface blowing from over-the-wing engines to generate high lift at low airspeed.
Compressed air is ejected from slots along the wing leading edges and just ahead of the flaps, which are deflected downwards 80deg. Flow from the slots also pulls the high-speed exhaust from the engines down onto the wing. Together these effects increase both the speed of the airflow over the wing and the curvature of its upper surface, increasing the lift coefficient by 8-10 times, says GTRI.
But it isn't that simple. The wing has to generate high lift on take-off and landing for short ground rolls and steep climb-out or approach angles, but also has to reduce cruise drag, noise and complexity to meet NASA's goals. Engine location relative to the wing is critical, says GTRI: closer to the wing helps STOL performance, but increases noise from scrubbing of the upper surface by the engine exhaust; further away helps noise, but to the detriment of STOL. GTRI's work is aimed at finding the configuration that works best.
Concept: Cal Poly