GB766621A - Improvements in or relating to controllable pitch propellers - Google Patents

Abstract

766,621. Variable pitch propellers. UNITED AIRCRAFT CORPORATION. Feb. 22, 1955 [March 1, 1954], No. 5277/55. Class 114. In a controllable pitch propeller comprising pitch changing mechanism movable along a path, a stop projectable into the path of said mechanism to limit the movement thereof, means for projecting and locking said stop in projected position and power means for withdrawing said projecting means from projecting and locking position, means are provided for returning the projecting means to projecting and locking position independently of said power means. The pitch of the blades 18 is altered by movement of a piston 32 and its associated cams 34, 28 causing rotation of blade gear segments 24. A governor 40 controls the supply of oil to, or exhaust from, lines 42 and 44. Line 44 leads via channels 48 and 50 and tube 158 to the front of piston 32, and line 42 leads via channels 46 and 258 to the back. The piston is formed with a sleeve 66 so that movement of the piston and sleeve to the left to reduce the pitch of the blades is limited by a stop 68 which is pivoted at 98 to a sleeve 168 adjustably threaded in a sleeve 170 secured to the dome 36. The stop is held in projected position by a wedge ring 84 slidable on a sleeve 174 carrying a shoulder 175. A plug 177 secured to sleeve 168 supports a spring 87 urging the wedge ring towards shoulder 175. The outboard end of sleeve 174 carries a piston 90 behind which is a cylinder space 92. The sleeve 174 and its piston 90 are urged to the right by a spring 86 pressing against a member secured to the sleeve 168 and a nut 178 on the sleeve 174. When the auxiliary motor 104 and pump 106 are energized oil under increased pressure is supplied to line 42 and flows behind piston 32 and also forces open a valve 100, Fig. 5, between tube 158 and sleeve 174 against the action of its spring 182 thereby obtaining access to space 92 to move the piston 90 and sleeve 174 to the left. Shoulder 175 moves wedge ring 84 to the left and the sleeve 66, moved to the left by its piston 32, depresses and passes over the stop 68, turning the propeller blades into a reverse pitch governed by stops 112. To unreverse the blades pressure is supplied to the left of piston 32 so that sleeve 66 moves to the right, the right of piston 52 and the valve 100 being connected to sump. Spring 182 closes valve 100, oil in space 92 is forced through drain passages 110, 108, 114 by the action of spring 86 which moves piston 90 and sleeve 174 to the right. As shown in Fig. 5 the shoulder 175 is moved from the wedge ring 84, so that the ring is urged by its spring 87 to move under stop 68 to project and lock same as soon as surface 94 of the sleeve 66 reaches hook 96 of the stop. The position of the piston 90 is determined by contact of a sleeve 180 forming part of sleeve 174 with the wedge 84. There is lost motion between the piston 90 and the wedge 84, the latter being moved into locking position by the spring 87 independently of the piston and without the necessity of draining hydraulic fluid from space 92. The piston 90 is used to hydraulically move the wedge 84 from locking position. Specifications 505,077, 607,856 and 636,402 are referred to,