GB836752A - A gas turbine aircraft engine coupled to drive a variable pitch propeller - Google Patents

Abstract

836,752. Propelling aircraft. GENERAL MOTORS CORPORATION. Aug. 13, 1958 [Nov. 22, 1957], No. 25989/58. Class 4. A gas turbine aircraft engine coupled to drive a variable pitch propeller, has mechanism which automatically causes feathering of the propeller on the application of reverse torque to the engine ; and a disabling device which renders this automatic feathering mechanism incapable of operating when a manual control is set to select reverse pitch of the propeller. A variable pitch propeller P mounted on a reduction gear assembly G is driven by a gas turbine engine E through a power shaft 10. The engine and propeller are controlled by a pilot's control lever 12 connected by linkage 13 to the input arm 14 of a co-ordinating control 16 which is connected by linkage 17 to an engine fuel control 18 and is also connected by a linkage 19, 21, bellcrank 22 and link 23 to an input control of the propeller. The propeller has two control rings 24, 26 mounted in a non-rotating part of the propeller hub and connected to the hydraulic pitch control mechanism within the propeller hub, the ring 24 having an arm connected to link 23 by which positive or negative pitch in fixed blade angle control, or speed governing operation, is selected, this condition being operated directly by lever 12 through control 16. The ring 26 has an arm 27 connected by a link 28 to a feathering control mechanism 30 which operates automatically in response to power or torque reversal between the propeller and the engine. In the preferred embodiment, Fig. 6 (not shown), such torque reversal is transmitted through co-operating helical splines, one connected to a fixed support and the other to the engine drive-shaft through the ring gear of an epicyclic reduction gear, so that upon reverse torque the ring gear performs axial movement and operates a plunger 51. When plunger. 51 moves forward it engages a rocker arm 52, pivotally mounted on pin 53, which arm bears on a rocker arm 54 mounted on shaft 55 provided, outside a housing 57, with a bellcrank 58, one arm of which is connected to link 28 and the other arm to a link 87 extending from a solenoid 85. Arm 54 is urged by a spring 92 into the position in which it does not transmit the feathering signal, this position being adjusted by a tappet 97. Consequently movement of plungers 51 results in rotation of shaft 55 and movement of arm 27 to feather the propeller blades, though such feathering may also be achieved by solenoid 85. In order that said feathering mechanism may be disabled when lever 12 is moved into the reverse thrust range, arm 52 has a recess 64 cut in its lower portion which may accommodate the full travel of plunger 51 when arm 52 is rotated about a shaft 61 by a solenoid actuator 78 operating through a linkage 76, 68 and 63, the solenoid 78 being energised through leads 80, 81 when a switch 82 is closed by a cam 83 on the lower end of lever 12.