Patent GB-514725-A (GB)
Title: Improvements in or relating to controllable pitch propellers
IPC: B64C11/40
Filed: 1938-04-13
Abstract: 514,725. Variable-pitch propellers. UNITED AIRCRAFT CORPORATION. April 13, 1938, No. 11349. Convention date, June 12, 1937. [Class 114] ' A variable-pitch propeller with hydraulic actuating mechanism is provided with a pressureresponsive means directly responsive to the pressure of the operating fluid for reversing the application of the fluid, thereto in response to changes in the pressure. The apparatus also provides for movement of the actuating gear within normal pitch range in response to a given hydraulic pressure, a movement outside that range to feathering position in response to a higher pressure, and a third movement-back from feathering position to normal in response to a yet higher pressure. Screw propeller 16 is connected by a piping 30, valve 28 and piping 26 with a 'pump 24 which is driven off the engine and which has a governing control 18. Under normal pressures therefrom the, fluid' passes by pipe 30 to the hub of the propeller and thence by internal tubes 34, 36 to the operating mechanism. When the pump 42 is brought into action its pressure being higher than that of pump 24 the valve 28 is moved by the pressure from pump 42 to shut off the pump 24 and pressure fluid then passes down through the pipe 30 as before. The immediate actuation gear in the blades of the propeller consist of bevel wheels 72. on the blade roots gearing with bevel wheels 82 adapted to be rotated by longitudinal movement of a slotted cam 84 into which enters a roller 102 carried by piston 106. The purpose of reducing the travel of the piston is to give a definite angular motion of, the wheel 82. The cam track'is divided into two parts, the upper part 88 being attached to the propeller boss and having its common slots 90 of opposite hand to the slots 86' in the cam 84 carried by the piston. The setting of the lower limit of pitch is effected by a stop 122 carried by the hub and contacting with the end of the cam slide 84. When normal operating pressures are used, the fluid,passes by way of the central tubes to space 148 and thence by a lead to the tube 168, this passage being open as ' a result of pressure acting upon the end 158 . of the valve 166 against the restraint of a spring 162. The pressure fluid is then passed along from the pipe 168 through a passage 208 and 178 to act upon the piston 106 and move it to the right to increase the pich. When the upper limitof normal range is reached a cam slide 188 carried by . a piston is moved to a position wherein a stop roller 186 is forced up. and forces a ball valve member 172 on to the seating 174 thereby cutting off the passage 178 and stopping further actuation of the piston. To produce feathering motion the higher pressure pump 42 is brought into use and the valve 166 is moved slightly to the right but not sufficient to cut off the entry to the pipe 168. At the same time the pressure in the pipe 168 is not sufficient to force the ball valve 172 .off its seating against the action of the spring 194 and fluid at the now higher pressure is supplied through pipe 178 to move the piston to the far end of its stroke and feather the blades. To return from this position a yet higher fluid pressure is used and the valve 166 is forced right over to cut off the supply to the pipe 178. In the' event of the pressure fluid exceeding safety working limits it passes by way of a safety valve to the drain pipe. The interior of the pipe 34 is coupled to the crank case and acts as a vent to gases passing away, through the end spring held valve 244.