Patent GB-938605-A (GB)
Title: Improvements relating to fuel control apparatus for helicopter gas turbine engines
Inventor: BEST STANLEY G
IPC: B64C27/32
Filed: 1961-01-31
Abstract: 938,605. Gas turbine plant. UNITED AIRCRAFT CORPORATION. Jan. 31, 1961, No. 3667/61. Class 110 (3). [Also in Groups XXIX and XXXIII] The invention concerns a fuel supply system for a gas turbine engine having a high pressure turbine driving the compressor of the engine and a low pressure free turbine driving the rotor of a helicopter. Fuel enters the system at 54 and passes through conduits 64, 66, a throttle valve 86, a conduit 70, shut-off and minimumpressure valve 72 and conduits 74, 56 to the burners, and the throttle valve, the pressure difference across which is held constant by a valve 144, is adjusted in the rotary sense by means 134, 138 responsibe to fuel temperature and in the axial sense by a servopiston 94 under the control of a valve 96 which is actuated by a lever 178 having a spring feedback connection 186 with the servopiston and a connection through an adjustable fulcrum 176 with a lever 174 actuated in accordance with absolute compressor discharge pressure by a bellows 166 opposed by an evacuated bellows 172. The fulcrum 176 is moved by a lever 290 having a roller 288 coacting with a cam 228 the arrange- 'ment being such that the fulcrum is positioned in accordance with the speed error, i.e. the difference between selected and actual speeds, of the compressor turbine. The error is measured by feeding to mechanism associated with the cam 228 an input from a selector cam 190 on a pilot's control shaft 188 and an input from a servopiston 266 under the control of a governoractuated pilot valve 248 which has a feedback connection 276, 250 with the servopiston. The cam 190 acts on the cam 228 through a lever 192, link 194 and linkage 196, 212, 236, &c., whilst the servopiston acts through levers 234, 222, &c. The servopiston 266 also actuates a threedimensional cam 296 which is rotated by rack and pinion 344, 346 by a servopiston 330 under the control of a valve 328 actuated in accordance with the compressor inlet temperature. The cam applies temperature correction to the pivot 218 of the lever 212, operates an acceleration limit stop 352 coacting with the lever 290, and operates a valve 542 which controls an inlet guide vane device (not shown) from which extends a feedback connection 554, 544, 540. A valve 362 which, together with the valves 96, 248 is rotated to reduce static friction, is actuated by a governor 360 driven by the free turbine and controls a servopiston 392 between which and the valve 362 is a feedback connection 426, 364. The servopiston 392 effects adjustment of the cam 228 through a lever 412 pivoted at 414, a lever 420 and the link 194. The lever 420 can also effect adjustment of the link 194 in response to action of a cam 458 mounted on a shaft 456 which is linked to the pilot's collective pitch control of the helicopter rotor. The pivot point 428 of the feedback lever 426 is adjustable by a member 450 and by a lever 440 subject to adjustment by members 452, 454 and a member 438 under the control of a cam 436 on the shaft 188. An overriding control to protect the free turbine from excessive torque consists of a lever 490 controlled by electrical signals and coacting with a nozzle controlling a servopiston 498 having a lever connection 530 with the link 194 and a feedback spring connection 536 with the lever 490. A valve 470 actuated by a cam 464 on the shaft 188 controls the shut-off valve 72 and unload the fuel pump of the system when the valve 72 is closed. Specification 753,970 is referred to.