Patent GB-533319-A (GB)
Title: Improvements in or relating to control systems for use with controllable pitch propellers
IPC: B64C11/30
Filed: 1939-10-12
Abstract: 533,319. Controlling variable pitch propellers. STEVENS, A. H. (United Aircraft Corporation). Oct. 12, 1939, No. 27781. [Class 114] An airplane propeller, having one range of pitch adjustment for normal operation and a second range of adjustment when diving, has an interlock between a manually releasable intermediate pitch stop and the throttle of the engine driving the propeller so that the releasing means for the stop can be maintained inoperative except when the throttle is locked in closed position. As shown, the pitch angle of a propeller is controlled to maintain the engine speed constant during a particular phase of operation by a governor 14, such as is described in Specification 470,284, and which is responsive to engine speed and has a manual adjustment 122. The propeller blades 18 can be rotated about their longitudinal axis by brackets 22 having counterweights 24, the' centrifugal force of which urges the blades towards high pitch condition. A hydraulic cylinder 26 slidable on a fixed piston is connected to the counterweights 24 by means such as is described in U.S.A. Specification 2,124,351, so that forward movement of the cylinder 26 moves the blades towards low pitch condition. The actuating fluid is regulated by a valve 74, Fig. 7. A manually actuatable combined throttle and propeller device comprises a bracket 28 with parallel slots 32, 34 connected by a gate 36 for guiding a hand lever 38. The latter can turn on mutually perpendicular journals 44, 48, and has an extension 55 with a transverse pin 56 the opposite ends of which can engage in apertures 58, 60, in levers 62, 64, pivoted on the journal 44. The handle 38 has a latch 50 engaging a stop 52 to prevent movement of the handle 38 out of the slot 34 except when the latch is raised. Movement of the levers 62 64, except when engaged by the pin 56 is prevented by spring detents 66, 68. The lever 62 controls the throttle opening so that the latter is controlled by moving the handle 38 in the slot 34. A mixture control handle 40 operates a lever 42 connected to the engine carburetter. The actuating lever 72 of the valve 74 is connected by a flexible cable 70 to the lever 64 and through a lost motion connection 80 to yoke 82 pivoted at 100 to the engine casing. A pair of latch members 84 pivoted to the propeller hub at 86, have, at one end, a hook 90 engageable with a ring 92 fixed to the cylinder 26, and at the other end are linked to the inner race 98 of a bearing, the outer race 102 of which is carried by the yoke 82. The handle 38 is moved into the slot 32 when it is desired to make a dive. Upon initial movement of the handle 38 the engine throttle will be locked in closed position by the detent 66 and a valve 116 cuts off the connection between the governor control valve 118 and a duct 110 leading to the cylinder 26. The governor cannot thereafter control the pitch setting. Movement of the handle 38 also connects the passage 110 to a drain passage 112 thus allowing the counterweights 24 to rotate the blades 18 into a higher pitch setting, thus slightly moving the cylinder 26 towards the propeller and freeing the hooks 90 from the ring 92. Continued movement of the handle 38 causes the passage 106 to connect the duct 110 with a high pressure duct 114. Thus hydraulic pressure is supplied to the cylinder 26 which moves forwardly and puts the blades into a low pitch setting so that they act as a brake during the dive and limit the airplane's speed. Upon return movement of the handle 38 in the slot 32 centrifugal force on the members 84 will cause re-engagement of the hooks 90 and ring 92. The propeller 12 has adjustable positive high pitch and low pitch limit stops incorporated in the counterweights as described in U.S.A. Specification 2,032,255.