GB746358A - Improvements in or relating to variable pitch propellers - Google Patents

Abstract

746,358. Variable-pitch propellers. UNITED AIRCRAFT CORPORATION. Aug. 18, 1954 [Aug. 19, 1953; Aug. 19, 1953], No. 24022/54. Class 114. In a propeller comprising a hub 30, blades 38, means for varying the pitch of the blades, a pitch lock engageable with the pitch varying means and fixed for rotation with the hub, and means for controlling the engagement and disengagement of the pitch lock, a latch is provided for holding the pitch lock in a disengaged position. Each blade has a gear segment 44 meshing with a common gear 46 actuated by a cam 48 turned by cam followers 50 movable by a piston 52 and co-operating with both cam 48 and a fixed cam 54. Oil supplied from a governor 53 moves the piston 52 to vary the propeller pitch to maintain a constant speed. The gear 46 and cam 48 have fixed thereto a toothed element 79 engageable by the spring- loaded pitch lock element 80. Normally high pressure fluid acting on the front of the piston 52 flows via passages 98, 96, 92, and through a rotatable valve 91 into a chamber 100 to hold the element 80 disengaged against the pressure of a spring 88. If a loss of pressure occurs in the chamber 100 due to loss of pressure on the front of the pitch changing piston 52, the springs 88 place the lock element 80 in engagement with the element 79. In order to prevent a lock-up unless an overspeed condition occurs a mechanical or hydraulic latch is provided. In Fig. 4 the mechanical latch comprises a cam 110 engaging a slot 112 in the lock element 80. In another embodiment the hydraulic latch comprises a check valve which closes to prevent the chamber 100 losing pressure due to fall of pressure acting on the front of the piston 52. The valve 91 has teeth 116 on one end which engage a spring- loaded centrifugal member so that at a predetermined speed the valve is rotated to align its port 130 with a port 132 which communicates with the chamber 100, at the same time closing off the passage 92 from the chamber. In this manner both sides of the lock element 80 are exposed to the same pressure, namely that in the hub chamber 72 and on the back of the piston 52, thereby permitting springs 88 to urge the element 80 into the locked position. The cam 110 is fixed to the valve 91 and rotates with it so that at said predetermined speed the cam moves out of the slot 112 to unlatch the lock element.