GB883865A - Aerofoil boundary layer control systems - Google Patents

Abstract

883,865. Boundary layer control on aircraft. POWER JETS (RESEARCH & DEVELOPMENT) Ltd. Sept. 16, 1959 [Sept. 17, 1958 ; June 16; 1959], Nos. 29802/58 and 20585/59. Class 4. An aerofoil boundary layer control system comprises an aerofoil with first and second side surfaces aud a rounded trailing edge surface, and formed with first and second spanwiseextending discharge apertures in its first and second side surfaces respectively, the apertures being arranged to discharge fluid streams as layers rearwardly over the side surfaces towards the trailing edge, and a control operable to vary the flow of the two streams relative to one another. An aerofoil comprising a wing 2 is of substantially elliptical cross-section and is formed in its surface with boundary layer control apertures or slots 10, 11, 12, 13, 14 and 15, each comprising a spanwise extending recess in the wing surface. Each recess has one surface 16 which fairs into the wing profile and another face 17 substantially normal to the surface 16 to form a step, face 17 being formed with discrete apertures 18 or slots which communicate with manifolds 21, 22 and 23 for slots 10, 11 and 12 and manifolds 25 and 26 for slots 14 and 15, respectively connected by conduits and valves 27, 33 ; 28, 34 ; 29, 35; 31, 37 and 32, 38 to a common manifold supplied with pressure air from an engine compressor or an auxiliary compressor, whereby compressed air may be supplied selectively to the slots. Similar provision is made for slot 13 and is shown in Fig. 3, air from slots 10, 11, 13 and 14 is directed towards the trailing edge of the wing whereas air from slots 12 and 15 is directed away from it. Under normal flight conditions valves 33 and 34 are opened to supply air to slots 10 and 11 such air emerging over upper and lower wing surfaces as sheet jets to provide a boundary layer control effect and, as shown at 39, Fig. 3, to close up the wake which would otherwise be set up round the trailing edge. By varying the relative mass flows and/or velocities of the air jets the rear stagnation point X can be moved from the neutral position of Fig. 3, to any point between slots 10 and 11 with consequent variation in circulation and lift on the wing, analogous to that normally effected by ailerons. To achieve a large increase in wing lift, the air supply to slot 11 is shut off while valves 35, 37 and 38 are opened to supply air to slots 12, 14 and 15 in addition to slot 10. At the same time air is supplied to slot 13 so that the stagnation point X is located between slots 12 and 13 resulting in considerable increase in life analogous to that normally effected by flaps. Slots 14 and 15 could be replaced by a single aperture or a greater number of apertures may be provided between apertures 10 and 11 to promote flow of the boundary layer around the wing trailing edge. The invention may be applied to tailplanes and fins of substantially elliptical cross-section or to helicopter rotor blades.