GB592458A - Variable pitch aircraft propeller - Google Patents

Abstract

592,458. Variable - pitch propellers. ENGINEERING & RESEARCH CORPORATION. May 1, 1945, No. 11042. Convention date, June 1, 1944. [Class 114] In a constant-speed, variable-pitch propellermechanism for aircraft in which propeller blades 16 are journalled in a hub 4 and rotated by axial movement, of a cylinder 20, the cylinder being actuated by pressure fluid under control of a valve 56 adjusted by the opposing forces of a spring 110 and a centrifugal governor 102, the force exerted by one member, e.g. the spring 110, is varied when the speed of the propeller attains a predetermined figure and the speed maintained thereafter at a different predetermined figure. Fig.. 1 shows the idling position with the cylinder 20 at its extreme right-hand position, the blades 16 set for minimum pitch and the valve 56 held at its extreme left position by the spring 110. A stationary piston 22 divides the cylinder 20 into two compartments. Lubricating oil &c. from a pressure chamber 28 in the crank-shaft 2, to which the hub 4 is secured, communicates through a passage 80, a port 82 in the piston 22, an annular space surrounding a reduced part of the valve 56 and a port 86 with the righthand chamber of the cylinder 20 to maintain the minimum pitch. On acceleration, the governor 102 displaces the valve 56 to the right and a land 64 thereon blocks the port 82. Further acceleration moves the land past the port permitting pressure fluid to enter the lefthand compartment of the cylinder 20 and displace the cylinder to the left, increasing the blade pitch. The resulting decrease in speed permits the spring 110 to move the land 64 to close the port 82. At its end remote from the governor 102, the spring 110 abuts against a flanged sleeve 156, Fig. 3, slidable on a second flanged sleeve 152 which is screwed on a tube 24 itself mounted in the hub 4 coaxially with the crank-shaft 2. At low speeds, the sleeves are held apart by balls 160 retained between a V-shaped groove formed by bevelling the edges of the flanges and a cylindrical member 120 secured to the cylinder 20. With increasing speed, the balls 160 move inwards along the inside of the member 120 and at a predetermined speed enter a groove in the member which partially frees them from the V-shaped groove permitting the spring to slide the first sleeve 156 into contact with the screwed sleeve 152 to increase the effective length of the spring, reduce the force with which it opposes the governor 102 and adjust the mechanism for a higher running speed. Successively deeper grooves may provide additional selected'speeds. To avoid excessive pitch change in any selected range, movement of the cylinder 20 is limited by stops 127, 124 on a sleeve 122, which are engaged by a flange 126 on the cylindrical member 120.