GB761235A - Improvements in or relating to air intakes for jet-propulsion power plants - Google Patents

Abstract

761,235. Gas turbine jet propulsion plant. ROLLS-ROYCE, Ltd. Feb. 16, 1954 [Feb. 24, 1953], No. 5197/53. Class 110 (3). An annular air intake for a jet propulsion engine comprises an annular shell the forward part of which is movable axially from the main part to form an annular gap at subsonic velocities below a selected value and a centre body with a pointed forward end which projects forwardly of the plane of the inlet to the annular shell at supersonic velocities above a selected value. The air intake shown comprises a circular annular outer shell 10 and a centrebody of circular cross-section. The outer shell has a sharp edge 10a at its forward end and its inner and outer surfaces 10b, 10c diverge at a small angle, say 3 degrees. The inner surface 10b is also slightly divergent with respect to the axial direction at a small angle, say 3 degrees, and is so shaped with respect to the centre-body that the area of the intake passage 12 increases for a considerable distance in the direction of air flow. The centre body has a sharp point 11b at its forward end. The sections 11c, 11d are so shaped that at supersonic speeds a series of relatively gentle shockwaves are formed at different points on the surface of the body 11, which shock-waves intersect on a circle lying in a plane at rightangles to the axis of the intake of greater radius than that of the annular outer wall. The section 11d is connected to the cylindrical surface 11f slidably mounted in a tube 13a forming part of a fixed fairing 13. The centre-body 11 is movable from the position shown to the position shown in chain lines by a piston 15 acting through a rod 15a. The forward end part 10f of the outer shell is movable axially forwards with respect to the main part 10e by means of rams 17. At a forward speed corresponding to a Mach No. of 1.0 the parts are in the position shown in which the point 11b is in the plane of the forward edge 10a. As the Mach No. is increased the angle between the shock-waves and the axial direction decreases. To ensure that the shock-waves are also intercepted by the shell 10, the centre body 11 is moved forwards at the Mach No. is increased. This movemens may be effected automatically by using the pressure rise which occurs across the shock waves when they are intercepted by the outer shell 10. Below a Mach No. of 1.0, the centre body 11 is held in the rearmost position and the forward end part 10f moved forwards to allow air to enter the gap between 10e, 10f. The movement of 10f may be a progressive one or effected at a particular Mach No. In a modification, the centre body is fixed but its apex is arranged forwardly of the plane of the edge 10a when the part 10f is fully retracted. The amount by which the apex protrudes is determined by the Mach No. for which the intake is designed. The arrangement is such that at this Mach No. the shock waves are just intercepted by the forward edge 10a. Specification 717,760 is referred to.