Patent GB-771513-A (GB)
Title: Improvements in or relating to variable pitch screw propellers
IPC: B64C11/38
Filed: 1955-04-13
Abstract: 771,513. Variable-pitch propellers. UNITED AIRCRAFT CORPORATION. April 13, 1955 [April 14, 1954], No. 10620/55. Class 114. An adjustable pitch propeller comprises a governor, governor-controlled means for adjusting the propeller pitch, decrease and increase pitch mechanisms connected with the governorcontrolled means for disabling the governor and actuating the pitch mechanisms, an auxiliary source of power and means actuated thereby for bye-passing the increase pitch mechanism and connecting the auxiliary source of power with the governor-controlled means for feathering the propeller while the first-mentioned pitch mechanisms are inoperative. A governor or engine actuated main pump 18 supplies hydraulic fluid at a relatively low pressure through a pipe 50 to a governor controlled valve 22 adapted to be raised to connect the pipe 50 though a pipe 40 to the increase side of the piston of a pitch-change motor 24 or to be lowered to communicate via a pipe 38 with the decrease side thereof. To actuate the valve, over-riding the governor, the pipe 50 communicates constantly with a pipe 54 leading to one end of a transfer valve 58 then through a filter 60 to a pipe 62, 63 connecting decrease and increase pitch valves 26, 28. These are operated selectively by solenoids 64, 78 and being opened pass fluid to the top or bottom chambers 70, 82 of the valve 22 through pipes 68, 80 respectively. The operating rods of the valves 26, 28 carry valves 74, 86 which close drainage pipes 76, 88 when they open the valves 26, 28. The crosssectional area of the chamber 82 is greater than that of the chamber 70 so that the increase pitch means can over ride the decrease pitch means. The propeller may be feathered independently of the pitch valves 26, 28 by an auxiliary pump 20 driven by an electric motor 92. The pump supplies fluid, at a higher pressure than that at which the pump 18 is working, to the end of the transfer valve 58 forcing it to the right to supply the fluid through a port 98 to the pipe 54 and so to the motor 24, fluid also flowing through a pipe 96, shuttle valve 100 and pipe 80 to the chamber 82 to raise the valve 22 and from the pipe 40 to the back of a low pressure relief valve. If the decrease pitch valve 26 should be open and the increase pitch valve closed, fluid can pass through the former from the filter 60 and pipe 63 to the pipe 68 and chamber 70 and also along the pipe 108 to force the shuttle valve 110 to the left, closing the upper end of the pressure line 80 and opening the line 88 to drain and through it the lower part of the line 80 leading from the chamber 82. Feathering and unfeathering are controlled by a switch 122 which, when moved to the right connects an electric power source 126 with a bar 128, contact 132 and the solenoid 78 actuating the increase pitch valve 28 while the bar also connects at 134 with the motor 92 of the auxiliary pump ; movement to the left connects the power with the bar 128, contact 124 and the solenoid 64 of the decrease pitch valve 26, and through the contact 117 with the pump motor 92. To reverse the propeller, a main switch 156 from a source 158 is closed and a reverseunreverse switch 154 moved from the unreverse position shown to its lower, reverse position where it contacts (1) a line leading to the switch arm 148 and thence to the decrease pitch solenoid 64 and (2) a line leading to holding coils 160, 162 for switches 168, 170 which short circuit the switches 154, 156. Movement of the switch 154 to the unreverse position (that shown) may connect it directly to the solenoid 78 of the increase pitch valve but as shown the auxiliary pump serves for this purpose. As the pump turns the propeller blade from position R through low pitch LP an earthed segment 174 thereon contacts the line 140 providing a path through a solenoid 176 which opens a switch 164 de-energizing the coils 160, 162 and opening the switches held thereby. In modifications, the increase pitch valve 28 or decrease pitch valve 26 or both the decrease and increase valves are coupled to the auxiliary pump 20 instead of the main pump 18. Specification 683,906 is referred to.