GB655562A - Improvements in or relating to propeller pitch control mechanisms - Google Patents

Abstract

655,562. Variable-pitch propellers. UNITED AIRCRAFT CORPORATION. Oct. 22, 1947, No. 28243. Convention date, Nov. 22, 1946. [Class 114] [Also in Group XXIX] The regulating valve 34 of the hydraulic motor 16 of a pitch-changing mechanism of the kind described in Specification 560,522 is controlled by a servomotor 70 having a differential piston 104, 106 loaded at one end by a spring 38 and at the other by a spring 122, the tension in which may be varied by a threaded sleeve 124. The opposite sides of the piston 104 are exposed to the governor pump pressure through pipes 68, 156, while the opposite sides of the piston 106 are subject through pipes 164, 172 to the pressures in the compensator cylinder 168 and the reservoir 60 containing the governor pump 56 which operates only while the propeller is rotating. In operation, when the engine speed falls below a pre-set value, pressure liquid is admitted to the opposite sides of the piston 104 which moves to the right and through the rod 72 operates the valve 34 so that the hydraulic motor 16 adjusts the propeller blade to its lowpitch position. Meanwhile, the liquid to the right of the piston 106 is forced through the pipe 172 to the reservoir, and the spring 122 is compressed. When the engine speed rises above the pre-set value, the pressure liquid from the pump will pass via the pipe 156 to the right-hand side of the. piston 104 which moves to the left and regulates the valve 34 so that the hydraulic motor adjusts the propeller blade to its high-pitch position. When the engine stops and the propeller ceases to rotate, the pump pressure falls to zero and the differential piston is moved by the springs to a position in which the propeller blade is adjusted to a position between its high- and low-pitch positions dependent upon the pressure applied to the spring 122 by the sleeve 124. Specification 14768/47 (as open to inspection under Sect. 91) is referred to.