Patent GB-683888-A (GB)
Title: Improvements in or relating to control systems for variable pitch propellers
IPC: B64C11/40
Filed: 1949-06-08
Abstract: 683,888. Variable-pitch propellers. UNITED AIRCRAFT CORPORATION. June 8, 1949. [June 10, 1948] No. 15248/49. Class 114. [Also in Group XXIX] A control system for a variable pitch propeller having a governor controlled constant speed range comprises an electrical circuit which energizes means for disabling the governor and moving the propeller blades into and out of feather and reverse pitch positions and electrical restoring means actuated directly by the movement of the blades for deenergizing the said electric circuit and automatically restoring the propeller to governor control when the blades reach a predetermined position in their return from the said feather on reverse pitch positions. The pitch changing mechanism comprises a hydraulic piston 34 in the propeller hub which rotates the blades through roller followers 30 in engagement with cam grooves 33 in a rotory member 28 connected through bevel gears 24, 22 with the blades. The rollers also engage oppositely sloping grooves 46 in a fixed cam 32. The ends of the cam grooves have steep slopes 42, 44 for moving the blades into feather and reverse pitch ranges. A. centrifugal governor 112, Fig. 5 operates a pilot valve 140 which controls the distribution of low pressure liquid, supplied by the engine lubricating pump 120 and a booster pump 114, 116, to either side of the piston. For moving the blades into feather or reverse pitch ranges, high pressure fluid is supplied by a pump 150 driven by an electric motor 160 which fluid acts on a land 216 of the pilot valve to disable the governor and is selectivcely distributed by this valve to either side of the piston 34. To feather the blades a switch 170 is pressed which closes the switch 166 of motor 160 and also energizes a holding coil 222 in series with a pressure operated switch 158. High pressure fluid is supplied to the inboard side of the piston 34 through pipe 154 valve 233 passages 132, 134, 144, 76, 84 and valve 102. When the blades reach the feathered position the cam mechanism engages a stop which causes a pressure surge whereby the pressure switch 158 is opened to de-energize holding coil 222 which releases switch 170 thereby stopping the high pressure pump. To unfeather, switch 170 is pulled to energize the holding coil 252 of a, relay switch 174 which closes the switch 166 of the motor 160 whereby high pressure fluid is supplied to the outboard side of piston 34 through passages 154, 132, 271, 146, 74, 80. The holding coil 252 is in series with a slip ring 262 on the hub of one of the blades. When the blades return to the normal range the slip ring interrupts the holding circuit of coil 252 which releases switch 174 to stop the high pressure pump. To reverse the blades switch 172 is moved downwards to energize relay switches 176, 178, 180 and thus cause the high pressure pump switch 166 to be closed. High pressure fluid is supplied to the outboard end of the piston 34 which moves the blades until the reversed position is reached when the cam mechanism engages end stops which cause a pressure rise to open the pressure switch 158 whereby relay switch 180 is de-energized and the high pressure pump is stopped. Relay switch 178 remains closed by engagement of its latch 314 with a spring-loaded armature 310. This relay controls the holding coil 326 of relay switch 176 which thus remains energized. To unreverse the blades, switch 172 is moved upwards whereby the high pressure pump is energized through relay switch 176. When the blades return to the normal range the slip ring 262 closes a circuit which energizes the coil 312 of armature 310 which thereby releases relay switch 178 which in turn releases relay switch 176 thus stopping the high pressure pump and restoring the propeller to the governor control. Blade de-icing elements 48, Fig. 1 are supplied with the current through a slip ring 52 and brush 54. The current supply to these elements may be controlled by a relay switch 390 whose coil 220 is in circuit with the coil 214 of the high pressure pump switch 166 so that when the latter is closed the elements are disconnected. The slip ring 52 may be replaced by a cam ring which co-operates with a plunger switch. Specifications 505,077 and 607,856 are referred to.