GB505077A - Improvements in or relating to controllable pitch propellers - Google Patents

Abstract

505,077. Fluid - pressure servomotor - control systems. UNITED AIRCRAFT CORPORATION. Aug. 4, 1937, No. 21532. Convention date, Aug. 4, 1936. [Class 135] [Also in Group XXXIII] In hydraulic-actuated pitchadjusting means for the blades of screw propellers, adjustment in the normal range is obtained with low pressure, stops preventing movement outside the range, whilst with higher pressure the blades are moved beyond to greater pitch positions for feathering. The blades 14 carry at their roots bevel wheels 162 meshing with a bevel wheel on a cam sleeve 30 having grooves each of two pitches 82, 88. Concentric with cam sleeve 30 is another 28 also having grooves of two pitches 78, 86. The piston 20 which is formed of concentric sleeves 21, 23 joined by a web 25 carries drive members 22 having ball-bearings 24, 26 engaging the cam surfaces' of the two sleeves whereby longitudinal motion of the piston produces rotation of the inner cam sleeve 30 and pitch adjustment. The piston 25 moves in a cylinder 18 and has packing 44 to maintain fluid tightness. Oil of low pressure from a pump 142 controlled by a centrifugal governor passes by pipe 150 to openings 32 and 36 in plugs 34 and 38 and thence through passages 40 to the side of the piston facing the propeller to alter pitch oppositely to the control imposed by the centrifugal force on the blades. The oil is free to pass to the cams and pitch actuating gear. The oil pressure is sufficient to move the piston so that the pins 22 follow the first pitches 78 and 82, but insufficient to utilize the steeper pitch grooves which act virtually as stops for. the normal range of pitch change To pass beyond this range to full feathering position, a pump 156 working at higher pressure is used, the oil moving through a chamber 152 to close a valve 160 'and cut out the pipe line 150 from the supply pipe to the propeller. With this higher pressure the piston is moved and the pins 22 pass along the higher pitch grooves 86, 88 in the cam sleeves. When a still higher pressure is used, oil passes through the valve 92 by passages 100 and holes 102 to the forward face as well as the after face of piston 25, which by reason of the annulus 90 has a greater area on the after face whereby the piston is moved back and the blades are returned from feathering position to the normal range. The tube 64 acts as a return conduit and is connected to the sump 140. A valve 108 is held open bya spring to allow oil to drain from the cylinder through holes 110 and tubes 52 and 64 when the pressure is released, but when pressure oil is passed to the cylinder it acts on the valve to close it. In addition when the piston has moved to the limit to the right, the nut 128 thereon contacts with a flange 130 on the valve 108 to open it. The cam sleeves have projections which may be engaged by discs which determine the high and low pitch positions. Specifications 355,329, 399,205, 416,255, and 470,284 are referred to.