GB812167A - Improvements in or relating to jet nozzles for jet-propulsion purposes - Google Patents

Abstract

812,167. Thrust reversal of aircraft jet, propulsion engines. ROLLS-ROYCE LTD. April 16, 1957 [April 17, 1956], No. 11722/56. Class 4. [Also in Group XXVI] A silenced jet nozzle with provision for thrust reversal comprises a fixed duct and a downstream nozzle portion movable axially between a first position in which it abuts the fixed duct and a second position spaced axially from the fixed duct to form lateral outlets, and blocking means having an inoperative position when the nozzle portion is in its first position and movable when the nozzle portion is in its second position, to an operative position in which the nozzle portion is blocked off at least partially and exhaust gas is constrained to flow through the lateral outlets. Figs. 1 and 3 show a jet propulsion engine in a fairing 11 mounted on a pod 10 of an aircraft. The fixed duct is corrugated at 12, the corrugations increasing in radial depth in the downstream direction. An apertured cup-shaped fairing 15 at the end of the duct has inwardly projecting tabs 15a, so that its central aperture corresponds to the cross-section of the duct at its downstream end, i.e. a central circular flow path and a series of peripherally spaced sectorshaped flow paths between the corrugations. The downstream nozzle portion 16 is similarly apertured with tabs 16a and is shaped so that it can nest on the fairing 15. A plate valve 20 is similarly apertured, having tabs 20a and is rotatably mounted on nozzle portion 16, being rotatable through gear teeth 21 on its rim engaging a pinion 22 driven by a motor 24. When the nozzle portion 16 is in its upstream position, the valve plate is positioned so that its tabs 20a are aligned with tabs 16a, and the exhaust flows rearwardly. For thrust reversal, the nozzle portion is moved rearwardly by a rack and pinion 17, 18, and valve plate 20 is rotated so that tabs 20a block off the spaces between tabs 16a and exhaust gas flows between the fairing 15 and nozzle portion 16 (arrows 28). The central aperture formed by tabs 16a and 20a may be blocked by a plug 26 normally enclosed in the pod 10. As an alternative, Figs. 5-7 (not shown), the nozzle portion may be moved axially by hydraulic jacks, and the central aperture formed on thrust reversal may be blocked by a series of triangular flaps pivoted on the tabs 16a and 20a and normally folded to lie against the tabs, but rotatable so that the free apices lie on the nozzle axis. Figs. 8-12 (not shown), illustrate an alternative wherein the pinion 22 is rotated by a helical slot and pin device operated by the hydraulic jacks which move the nozzle portion axially. Also, the central aperture formed on thrust reversal is blocked by folding flaps pivoted on three of the six tabs 16a only, each flap unfolding on extension to block off a one hundred and twenty degree sector of the aperture. Fig. 16 shows an embodiment for a by-pass engine, comprising a main duct formed by a wall 80 and a bullet 81 and a by pass duct formed by walls 83, 84. The downstream nozzle portion comprises a double wall 87 continuing walls 80, 84, a wall 88 continuing wall 83, and inwardly projecting members 90 increasing in radial depth in a downstream direction to divide the gas path at the nozzle outlet into a series of sector-shaped peripherally spaced flow paths, so that although wall 87 is divergent, the flow path is convergent. With the nozzle portion in the downstream position shown, a pair of eyelids 94 pivoted to the fixed duct, are moved to the position shown, diverting the gases to lateral outlets 93. For normal operation, the eyelids are swung back and the nozzle portion retracted, the eyelids then lying between wall 88 and fairing 91. Figs. 13 and 14 (not shown), illustrate a modification in which grids of circumferentially extending guide vanes are placed in the outlets 93. Fig. 22, shows an application to a by-pass engine, wherein in the thrust reversal position shown, the nozzle portion is blanked off by triangular flaps 140 pivoted to the downstream nozzle portion and linked by rods 142 to the bullet 121 of the fixed duct. On retracting the nozzle portion, the flaps 140 are swung by links 142 to lie parallel to a wall 126, and in this position the flaps divide the exhaust gas flow from the by-pass air. Silencing is achieved by a plurality of tongues 130 pivoted at the downstream end of the nozzle, and operable by a jack 129 so that alternate tongues are inclined inwardly and outwardly of the nozzle. As alternatives to the plates 140, eyelids may be used which divide the exhaust flow from the by-pass flow in the normal position of the nozzle portion, Figs. 19 and 20 (not shown), or eyelids similar to those of Fig. 16 may be used, see Figs. 17 and 18 (not shown).