Aircraft Engine Intake Ducts

摘要

1,166,733. Boundary layer control. MINISTER OF TECHNOLOGY. 14 Feb., 1968 [14 Feb., 1967], No. 6916/67. Heading F2R. [Also in Division F1] An aircraft engine air intake duct has means movable transversely of the airflow into the duct between a retracted position at subsonic airspeeds and an extended position at supersonic airspeeds, the movable means in the extended position causing the boundary layer flow over an associated upstream aerodynamic surface to leave the surface, and bleed means downstream of the movable means to bleed off at least some of the deflected boundary layer from the main flow through the intake duct. In one embodiment, Fig. 3, the engine intake duct 23 is of generally half-moon end section and is defined between a part of the aircraft fuselage 21 and an enclosure 22. A wall 24 is mounted in the fuselage and is movable transversely of the airflow through the duct 23 between a retracted position at subsonic airspeeds and an extended position, shown, at supersonic airspeeds. The movement is effected by a member 25 controlled manually by the pilot or automatically in accordance with airspeed. In the extended position the wall 24 reduces the flow area of the duct 23 and at the same time causes the boundary layer flow to separate from the fuselage upstream of the wall 24, the separated layer being drawn off through a bleed aperture 26. The separation causes the formation of shock waves C and D. Aerodynamic efficiency can be improved by jets of air 27 supplied by a pump 28 to increase the boundary layer velocity and by drawing off an additional portion of the boundary layer through an aperture 29 by means of a suction pump 30. Further air jets at 31 and/or 32 may assist the bleed flow through aperture 26 by ejector action and additional assistance may be provided by a pivoted flap 33 adjacent aperture 26 movable into the position shown dotted during supersonic operation. In a modification, Figs. 4 to 6 (not shown), the intake duct (41) is cylindrical having a conical central spike (42) and the movable wall is formed by an annular assembly of interfitting segments (43), the deflected boundary layer passing through a bleed aperture (45) to the interior of a hollow centre body (46). In a further modification, Fig. 7 (not shown), the intake duct (71) is rectangular having a wedge-like centre body (72). In a further arrangement, Fig. 8 (not shown), the movable wall (84), is mounted on a rectangular or circular intake (81) rather than on the centre body (83).