GB796291A - Improvements in nozzles for the discharge of elastic fluid - Google Patents

Abstract

796,291. Jet propulsion nozzles. BRISTOL AERO-ENGINES, Ltd. Aug. 31, 1956 [June 2, 1955], No. 15886/55. Class 110 (3). [Also in Group XXIX] A nozzle for the discharge of an elastic fluid comprises a convergent part, a first divergent part joined to the convergent part, and at least one further divergent part which is movable from a position in which it is ineffective to a position in which it constitutes a divergent extension of the first divergent part. In the jet propulsion nozzle shown in Fig. 1, the convergent part 3 is followed by a divergent part 4 at supersonic speeds. At transonic speeds of, say, a Mach number between 1 and 1.3, a portion 5 of the divergent part 4 is retracted telescopically over the remaining parts of the nozzle so that only the latter parts remain effective. The part 5 is moved to and from the retracted position by one or more double-acting pneumatic or hydraulic jacks 6, Figs. 1 and 3, the supply of motive fluid being controlled by a shuttle valve 7 operated manually or, preferably, by a device 8 which is responsive to the working pressure ratio of the nozzle, i.e. the ratio between the ambient static pressure sensed by a static pressure orifice 9 and static pressure in the jet pipe 1 sensed by a static pressure orifice 10. The changeover is arranged to occur at about the working pressure ratio at which the pressure on the part 5 is zero, i.e. at which the same thrust would be developed with the part 5 in either the extended or retracted positions. Friction of the rod 17 in its bearings, augmented by a resiliently applied friction pad 23, ensures stable operation by causing the extension to occur at a somewhat higher pressure ratio than the retraction. The device 8 may, as shown, comprise a casing 11 divided into chambers 12, 13, 14 by a diaphragm 15 and a bellows 16. Chamber 14 is connected to the orifice 9 by a conduit 30, and chamber 13 is connected to the orifice 10 by conduits 31, 32. Chamber 12 is connected by a conduit 20 to a pressure potentiometer comprising an upstream restriction 18 and a downstream restriction 19, one of which, say the restriction 18, preferably being made adjustable. During operation, the flow through the restriction 19 is choked. Means may be provided for cooling the exhaust gases flowing through the orifice 10 and conduit 32. The bellows 16 may be replaced by a second diaphragm, smaller than the diaphragm 15. In a modification, chamber 14 is evacuated, chamber 12 is connected to the pressure potentiometer, and chamber 13 is connected to the orifice 9. Retraction of the nozzle part 5 may be effected by displacing it in the direction of flow of the jet stream or laterally thereof. Two or more retractable and extendable nozzle parts may be provided and moved into the extended positions successively as the working pressure ratio increases. Where the nozzle forms part of an expendable unit, the operating means may move the extendable part into the extended position only, no provision being made for a return to the retracted position.