Abstract:
Distributed suction may be preferable to tangential blowing as a method of boundary-layer control to achieve high lift for civil aircraft, because of its lower flow rates and power requirements. Tests using practical perforated suction surfaces at the knee of full-span L.E. flaps are reported, for conventional hinged flaps and for an extending-area arrangement having increased knee radius. Stalling incidence increased progressively with suction rate. With T.E. flaps extended, a CQ of 0.0024 increased CLMAX from 2.17 to 2.68, and from 2.47 to 2.80 for hinged and extending L.E. flaps respectively : increments with T.E. flaps retracted were similar. Flow requirements were insensitive to perforation arrangement and were little affected by simulated heavy rain; they were significantly reduced by increase of open-area ratio (with accompanying fall of plenum chamber depression and suction power) and increased by surface imperfections and intersurface leaks. Extending-area L.E. flaps may have advantages even without B.L.C., if mechanically practicable.
