Patent GB-683757-A (GB)
Title: Tailpipe or afterburning control for turbojet engines
IPC: F02K1/16
Filed: 1949-03-14
Abstract: 683,757. Jet propulsion gas turbine plant. BENDIX AVIATION CORPORATION. March 14. 1949 [June 3, 1948], No. 14045/51. Divided out of 683,690. Class 110(iii) [Also in Group XXIX] A gas turbine jet propulsion engine with reheating in the jet pipe having means for metering the reheating fuel and means for varying the area of the jet nozzle has a device responsive to engine speed which operates on the two control means to maintain the relationship or reheat fuel flow to jet nozzle area. The fuel supply to the reheat burners is controlled by a unit 260 and the area of the jet nozzle by a unit 151. A fuel pump 91 supplies fuel to a chamber 261 in which the pressure is maintained at a constant predetermined value over and above the metered fuel pressure by means of a by-pass valve 262 connected to a spring loaded diaphragm 263. A regulator valve 268 controls a port 269 through which fuel flows into the chamber 270. A diaphragm 271 backed by a spring 273 controls the valve 268 so that a constant pressure drop is maintained across the diaphragm. From chamber 270, the fuel flows through passage 110, 110<SP>1</SP>, metering restrictions 121, a throttle valve 111 and conduit 116 to the reheat manifold. Fuel may also flow from the chamber 270 to the conduit 116 through a parallel path including a passage 274, a variable orifice 276 controlled by needle valve 277 actuated by bellows 278 responsive to changes in air density at the inlet of the compressor, chamber 272 and bleed 280. As the pressure across the diaphragm is maintained substantially constant and as the chamber 272 is related to that in the conduit 116, the flow of fuel to the reheat burners, under steady conditions, will remain constant for any given position of the piston valve 111. This flow is varied according to altitude conditions by the needle valve 277. As the pressure drop between the chambers 270, 272 is maintained constant, the flow through the orifice 276 will vary according to the position of the needle 277. Since this flow also passes through the fixed orifice 280, the pressure drop across this orifice will also vary resulting in corresponding reduction of pressure drop across the metering orifice 121. The means for varying the orifice area is the same as that described in Specification 683,390 and comprises a servo-motor supplied with operating fluid by a servo-valve 140. the slide 138 of the servo-valve 140 is pivotally connected to a servo-lever 137 having a pin and slot connection with the rod of the servo-motor piston operating the variable area jet nozzle. This slide is operated by a diaphragm 152, which divides a casing into a pair of chambers 153, 154, through the rod 155 and servo-lever 137. A spring 158 acting on a piston 159 connected to the rod 155 urges the diaphragm 159 and hence the valve land 139 to a neutral position where it closes the port 143. The position of both the diaphragm 152 and the spring loaded piston valve 111 are determined by the pressure drop across a diaphragm 161 which is determined by the pilot control lever 180. The lever 180 controls the loading of a spring 172 acting on the diaphragm 161 which controls the pressure drop. by means of a valve 165. A speed governor 281 controls a servo-valve 284 regulating the supply of pressure fluid to the conduits 292<SP>1</SP> and 199<SP>1</SP> leading to the chamber 200 at the back of the piston 111 and the chamber 202 at the back of the piston 159. The arrangement is such that any variation of the turbine speed from the normal will cause the valve 11 to close the ports 121 and open the variable area jet nozzle or vice versa.