GB873173A - Variable area jet propulsion nozzles - Google Patents

Abstract

873,173. Jet propulsion plant. POWER JETS (RESEARCH & DEVELOPMENT) Ltd. May 9, 1958 [April 2, 1957], No. 10729/57. Class 110 (3). In a variable area jet propulsion nozzle having an outer casing and an axially movable centrebody, the centre body is enlarged adjacent its downstream end and comprises a central support and an enclosing outer skin which is secured to the support at its downstream end only so that it is free for thermal expansion relative thereto, and passages are formed between the support and skin for the flow of cooling fluid, these passages being arranged to discharge the cooling fluid over the outer surface of the skin. As shown in Figs. 1 and 2, the centre body 10 comprises a central tubular support 31, and a thin sheet metal outer skin 32 forming a stem 32a and an enlarged downstream part 32b of generally ovoid axial cross-section constituting the plug or " bullet " 9. Within the bullet there are two frusto-conical members 35, 36 secured to the outer skin. The rearward 36 of these two members is further supported from the tubular support 31 by a number of ribs 37 while the forward member 35 is supported from member 36 by a number of spacers 38. Fuel is supplied to injectors 13, 15 by pipes 17, 18 controlled respectively by valves 19, 20. Cooling air, supplied by a pipe 27 to the interior of a hollow fairing 7, flows rearwardly between guide blocks 39 to the ovoid bullet where it is divided by the member 35, part flowing through inclined circumferentially overlapping slits 43 and the remainder escaping through similar inclined slits 44 to cool the rearward part of the plug. The downstream extension 41 of the fairing engages with stem part 32a of the outer skin through a thin bent sheet metal ring 42, Fig. 4, secured at its rearward end by welding to the extension 41 and resiliently engaging at its forward end against the cylindrical part of the bullet skin 32. The ring 42 is formed with keyhole slots 42a to permit radial thermal expansion. The variable area jet nozzle is operated by an hydraulic jack 22 mounted within the fairing 7, the cylinder being anchored at its end to a transverse wall 23, and an operating rod 24 being connected to move the centrebody. In a modification of the bullet, Fig. 8, the outer skin is made up of a number of overlapping parts or shells 51, 53, 55, 56 providing annular discharge apertures or gaps 54, 57, 58, allowing the surface of the centre body facing the jet stream to be cooled externally. In a further modification (Fig. 11, not shown), the enclosing skin is formed by the outer wall of a sleeve of double-walled construction, providing between the two walls, a passage for the flow of cooling fluid. Also included in a tubular fairing the downstream end of which embraces the upstream end of the enclosing skin and is spaced therefrom to provide a flow path for the cooling fluid from the space between the double walls of the centre-body into the jet stream. In this modification the outer casing is formed with an outward bulge located opposite the enlarged portion of the enclosing skin when the centre-body is in a forward position. The skin supporting arrangement of Fig. 4 may be replaced by an arrangement comprising a circumferential series of mating elements embraced by a garter spring to hold them in contact with the stem 32a of the outer skin 32. In any of the above embodiments, the centre body may be held in any intermediate position in its range of movement or in any of a definite number of positions, determined for example by the magnitude of the fuel supply or the pressure in the combustion chamber. Specification 684,669 is referred to.