GB700394A - Improvements in or relating to pitch changing mechanisms for propellers - Google Patents

Abstract

700,394. Variable-pitch propellers. UNITED AIRCRAFT CORPORATION. Oct. 30, 1951 [Nov. 1, 1950], No. 25338/51. Class 114 A variable-pitch propeller having a fluidoperated pitch changing motor operative to move the blades in a normal range and a reverse-pitch range, comprises co-operating elements 33, 150 operative where the blades reach a predetermined reverse pitch position for limiting the pressure acting on the motor piston 32 to that which is only sufficient to overcome the force exerted in the opposite direction due to the centrifugal blade twisting movement which tends to move the blades towards the low-pitch position during rotation. The movement of the motor piston 32 in the low pitch position of the normal governor-controlled constant-speed range is limited by stops 68 which are engaged by a sleeve 35 secured to the piston. The stops are held outwardly by a wedge 90 loaded by a spring 92 and secured to a sleeve 96, loaded by a second spring 110, which carries a piston 104 operable in an axially adjustable cylinder 72. For reversing the blades high pressure liquid supplied by a pump 122 through passages 44, 48 to the inboard side of the piston 32 acts through an annular passage 120 and opens a spring loaded sleeve valve 130 whereby the pressure liquid acts on the inboard side of the piston 104 and moves the latter and the wedge 90 outwardly thereby releasing the stops 68. At the extreme reverse pitch position, bleed ports 150 in the sleeve 35 move past a packing ring 33, carried by an axially adjustable sleeve 38 and place the opposite sides of the piston 32 in communication with one another thereby limiting the movement thereof. A mechanical reverse-pitch stop may also be fitted. Specifications 505,077. 514,725,607,856 and 636,402 are referred to.