Patent GB-866525-A (GB)
Title: Variable pitch propellers and control systems therefor
IPC: B64C11/40
Filed: 1959-10-08
Abstract: 866,525. Variable pitch propellers. GENERAL MOTORS CORPORATION. Oct. 8, 1959 [Oct. 10, 1958], No. 34119/59. Class 114. A control system (shown schematically in Figs. 1A-C) for a variable pitch propeller having blades 14 rotatable about their longitudinal axes between maximum negative and fully feathered pitch angles by fluid pressure operated motor means (piston 20 in cylinder 18) has a source of fluid under pressure, a speed sensitive governor (the centrifugal mass of which has its centre of gravity at 412 and comprises a plunger 396 and a centrifugally responsive lever 410), a valve 370 operated by the governor for controlling flow of pressure fluid to the pitch adjusting motor, a manually operable control (lever 584) for the governor having a forward thrust constant-speed governing position wherein the pitch of the blades can be adjusted between minimum and maximum positive angles and a reverse thrust constant speed governing position wherein the pitch of the blades can be adjusted between maximum and minimum negative angles, and means (fulcrum 420 of lever 410) actuable by the manual control for reversing the sense of the governor during movement of the manually operable control from the forward thrust to the reverse thrust governing position. The system includes adjustable means (rod 528) constituting a port of said governor having a first position wherein the governor operates valve 370 to adjust pitch of blades towards feathered position during propeller over-speeding means (actuator 186) for adjusting last mentioned means (rod 528) to a second position wherein the governor operates valve 370 to adjust pitch of blades towards maximum negative pitch in response to propeller speed, and means (cam follower 568) actuated concurrently with adjustment of first mentioned means (rod 528) between said first and second positions for overriding the governor and actuating valve 370 to effect movement of the blades from positive to negative pitch. Lever 584 is pilot controlled and attached to a ring gear 582 in mesh with a pinion 580 on a screw 578 to effect axial movement of a non-rotating control ring 474 having follower shoes 490 and 492 connected to rods 491 and 508 respectively. The lever 410 has a slot 422 for the fulcrum 420, surfaces 570 and 574 engageable by rollers 568 and 572 on cam slotted levers 556 and 558, and is loaded by a spring 416 via a rod 414. Plunger 396 is connected to lever 410 at 408 and movement of the plunger operates the distributer valve 370. Pressure fluid is supplied by pumps 128, 130, 132 driven incident to propeller rotation, pump 132 delivering to an auxiliary pump control valve 142. The high pressure supply conduit 140, Fig. 1A, leads to a feathering valve assembly 178 Fig. 1B, with conduits 36, 38 communicating with the cylinder 18, Fig. 1C, of the pitch change motor. The piston 20 has helical spline teeth 24 and 26 mating with teeth 22 in the cylinder wall 18 and teeth 28 on a fixed member 30 so that reciprocation of the piston is accompanied by angular movement thereof which is imported to the blade 14 which is journalled by stack bearings 16 in the hub 10 and connected to a bevel gear 40. The several blade gears 40 mesh with a bevel gear 42 having ratchet teeth 46 engagable by teeth 48 on an annulus 50 to form a mechanical pitch lock since engagement of the teeth allows rotation of the blades to increase pitch but precludes rotation to decrease pitch. A conduit 120 feeds a feathering reservoir 106 housing an electrically driven feathering pump 108 delivering to a conduit 110 and a mechanically driven feathering pump 112 delivering to a conduit 118. A rotary feedback shaft 98 engages a nut 102 on a rod 104 connected to a lever 566, Fig. 1B. The lever 566 is pivotally connected at 618 to a lever 616 and at 564 to a rod 562 the other end of which, Fig. 1A, pivotally interconnects the levers 556 and 558. When the propeller is operating in the forward thrust range, movement of the control lever 584 with resultant movement of rod 491 and cam 440 attached thereto and hence of cam follower 442 and lever 428, alters the compression of the spring 416 and thus the speed setting of the governor. An electronically controlled solenoid valve 180, Fig. 1B, is connected in a parallel flow path with the servo distributer valve 370. The pilot can feather the propeller at any time by energising solenoid 230 in the valve assembly 178. When the control lever 584 is moved to the reverse governing range, rod 508 is moved so that cam follower 510 causes operation of actuator 186 to move rod 528 whereby the fulcrum 420 is moved to the other side of the centre of gravity 412 to reverse the sense of the governor. Concurrently the roller 572 is moved out of engagement with cam surface 574 and roller 568 is moved to engage surface 570, the resultant downward movement of plunger 396 moving the blades to the minimum negative pitch angle. A jitter plunger 468 is connected via a conduit 470 to pulsate oil in chamber 406 to reduce static friction. The rod 508 carries a cam plate 511, Fig. 1B, and a cam follower 514. The plate 511 is slotted for followers 601 and 614, the follower 610 forming part of a pitch lock and pitch stop control valve assembly 182 and the follower 614 being connected to the lever 616. The follower 514 is disposed in a slot 621 in a lever 622 pivotally connected to a selector valve 236. A second slot 626 in the lever has a follower 628 on a rod 630, the other end of which, Fig. 1A, is connected to a shoe 634 on a ring 476 moved axially via screw 636 and pinion 638 by a lever 642 actuated by a negative torque sensing mechanism. A synchronizer control lever 488 imports axial movement to a shoe 478 which moves a cam 436. A cam follower 434 adjusts the position of a plunger 430 to vary the load on the governor spring 416. The delivery conduit 110 of the feathering pump 108 connects with a centrifugally operated control value 252. The propeller hub and the feathering reservoir 106, Fig. 3, are enclosed by a spinner shell 75 having a central air inlet 77. The shell 75 is formed with islands of airfoil shape forming a continuation of the airfoil portion of the propeller blade 14 when the blades are in a predetermined angular position. A regulater pump supplies lubricating fluid to bearings, Specifications 724,855 and 836,941 are referred to.