Patent GB-1069130-A (GB)
Title: Propellor pitch changing mechanisms
IPC: B64C11/38
Filed: 1965-07-27
Abstract: 1,069,130. Variable-pitch propellers. UNITED AIRCRAFT CORPORATION. July 27, 1965 [July 30, 1964], No. 31919/65. Heading B7V. A variable-pitch aircraft-propeller comprises a plurality of blades 16 mounted in bearings 18 on a hollow rotatable-shaft 12 and controlled by an hydraulically-actuated motor having a piston 24 fixed to a stationary shaft or tube 22 and a non-rotatable axially-movable cylinder 26 linked to each blade by a roller 48 engaging with a cam 46, the motor being controlled by a rotatable valve-member 40, which is slidably mounted on the shaft 22 and coupled to the cylinder 26 by screw-threads 96 to effect " negative feed-back " from the motor to the valve-member. To increase the pitch of the blades, the valve-member 40 is moved relative to the cylinder 26 so that a pressurized liquid is supplied to chambers 34, 50, which are associated with the cylinder, through channels 38, 44, 52 in the shaft 22 by way of the valvemember while liquid in a further chamber 32 associated with the cylinder is ejected through other channels 42, 70 in the shaft 22, the pitch being increased until the cylinder brings the valve-member into a " null position " wherein it closes ports 72, 74 at the ends of the channels 42, 44. Pitch-reduction is effected by appropriate movement of the valve-member relative to the cylinder to cause pressurized liquid to enter the chamber 32 while liquid is ejected from the chambers 34, 50 until the valvemember is again brought to a " null position " by the motion of the cylinder. Movement of the valve-member relative to the cylinder is rendered by the action of the screw-threads 96 when a gear-wheel 98 at one end of the valvemember is rotated by an hydraulic motor 110 through gearing 104, 102, 100, the motor 110 being controlled by a governor 114 and having a rotatable casing coupled by further gearing 108, 106 to the shaft 12. The valve-member is moved relative to the cylinder when the gearwheels 104, 108 rotate in either direction with respect to each other. During " overspeed" conditions, the governor opens a port (111), Fig. 2 (not shown), so that the motor 110 can function as a pump and permit rotation of the gear-wheel 104 relative to the gear-wheel 108 due to friction between the gear-wheels 100, 102 with consequent rotation of the gear-wheel 102 in a direction opposite to that of the shaft 112 and a corresponding increase in the bladepitch. During " underspeed " conditions, the governor causes the motor 110 to be fed with pressurized oil from a reservoir (113) by a pump (115), whereby the gear-wheel 104 drives the gear-wheel 102 at a speed exceeding that of the shaft 12 and causes consequential pitchreduction. In the event of failure of the hydraulic system, a valve 123 is opened to connect a liquid-supply pipe or line 36 to a drain connection 70, axial movement of the cylinder and valve-member due to rotation of the blades by centrifugal action being restricted by a flange 116 on the valve-member abutting a race 122, which is supported by rollers 120 and a race 118 fixed to the shaft 12. The blades may be feathered when such a failure occurs by applying a brake 138 to a flange 136, which is connected to the valve-member by gearing 126, 128, 130, 132, 134 and friction between the race 122 and the flange 116 whereby the valve-member is rotated relative to the cylinder, owing to blades " wind-milling," and displaces the cylinder until feathering is adequate to prevent further " windmilling." " Spring washers 140 may be lodged between the cylinder and the race 118 to increase the friction between the flange 116 and the race 122. Rotation of the cylinder relative to the shaft 12 is prevented by splines 95. Pitch-reduction may be limited by a plurality of fingers 54 forming an abutment or stop for the cylinder, the fingers being retracted when a cone or wedge 66 is displaced towards the cylinder by pressurized liquid acting on a piston 62 against the action of springs 64, 68. Pressurized liquid is supplied to a chamber 60 associated with the piston 62 through a channel 58 in the shaft 22.