GB910467A - Improvements in or relating to air intakes for supersonic aircraft - Google Patents

Abstract

910,467. Jet-propulsion plant. ROLLSROYCE Ltd. Dec. 11, 1959 [Dec. 11, 1958], No. 40072/58. Class 110 (3). An engine intake for supersonic aircraft comprises a fixed wall having a leading edge lip and a second wall including pivoted flaps extending from upstream of the lip to downstream of the lip, the intake area being determined by the position of the flaps relative to the lip and the flaps also forming walls of a chamber having such communication with the intake air flow adjacent a shock wave forming at the lip under some conditions of supersonic flight that the internal pressure acting on the flaps has a value between the external pressures acting on the flaps upstream and downstream of the point of communication so that the flaps are loaded differentially and take up an equilibrium position. The intake, Fig. 2, comprises a pair of opposite main walls 10 terminating at their upstream ends in lips 10a forming fixed structure and a centre body comprising two pairs of flaps 12a, 13a and 12b, 13b, the one pair co-operating with one of the walls 10 to define a first intake passage and the other pair cooperating with a second wall 10 to define a second intake passage. The flaps 12a, 12b, 13a, 13b are pivoted to the upstream and downstream ends of a fixed wall 14. The flaps 12a, 13a and 12b, 13b are separated by gaps 16 which place a chamber 17 defined by the flaps and the wall 14 into communication with the air flow through the intake. The flaps are interconnected by arms 19 and pin-and-slot connections 20. In supersonic flight inclined shock waves 21 are formed by the upstream edge of the wall 14 and at supersonic speeds above Mach 1.4 shock waves 22 are formed at or adjacent the lips 10a and the intake is so designed that the shock waves are level with and inclined across the gap 16. The latter effect can be obtained by either profiling the lips 10a or by arranging the gap at an angle to the transverse axis of the intake. As a result of this inclination of the shock waves, the pressures in the chambers 17 has a value between the low pressures acting on the flaps 12a, 12b upstream of the waves 22 and the high pressures acting on the flaps 13a, 13b downstream of the waves 22 and the pairs of flaps 12a, 13a and 12b, 13b will take up positions of equilibrium when the loads due to the pressures are balanced. If the aircraft supersonic speed increases the shock waves 22 tend to move upstream causing an increase in pressure in chambers 17 and outward swinging of the flaps to reduce the intake area which results in a rearward displacement of the shock waves until a new equilibrium position of the flaps is reached. To enable the intake area to be selected for given dimensions of the flaps 13a, 13b, flexible bellows 24 are connected between the wall 14 and the flaps 13a, 13b and vents 23 formed adjacent the downstream edges of the flaps. In a modification, Fig. 3 (not shown), the flaps are slightly convex towards the intake air flow. In this arrangement, the shock wave at the lip 10a strikes the upstream flaps upstream of the lips. The gaps 16 are sealed from the chambers 17 and a series of axially-spaced holes are formed in the upstream flaps at the region where the shock waves strike them. In another modification, Fig. 4 (not shown), the holes in the upstream flaps are covered and uncovered as the flaps move inwards and outwards by valve members attached to the flaps. The intake may be formed as half the intake described and may be attached to the side of the fuselage. Damping devices may be connected to the flaps. These may be an hydraulic shock absorber or a rack which drives a pinion carrying a friction disc which co-operates with a fixed surface.