Patent GB-480747-A (GB)
Title: Improvements in variable-pitch airscrews for aircraft
IPC: B64C11/42
Filed: 1936-08-25
Abstract: 480,747. Variable-pitch screw propellers. EVANS, A. F., and WELLS, R. G. Aug. 25, 1936, Nos. 23337 and 27130. [Class 114] In variable-pitch screw propellers with hydraulic adjusting gear, a reciprocating pump is carried by the hub and yielding means or centrifugal forces are employed to effect the delivery stroke. Where the blade is intended to be set to low pitch position by air forces, the hydraulic motor may be used for one-way movement, and its limit of movement may be controlled by a second hydraulic ram. These hydraulic rams are housed in cylinders within a sleeve slidable upon the air-screw shaft. Each blade has at its root 13 an eccentric pin 14 which engages a block 16 of cylindrical form which is slidable in a casing 17 attached to a main sleeve 19. This latter is adapted to slide upon a sleeve encircling the propeller shaft and has end closure flanges 20, 21, the sleeve enclosing an annular block 28 which has a forward extension 27 that fits into a front housing 30. The housing is attached to the hub 10 and carries a domed cap 33. Within the housing are four pumps each comprising a plunger 41 carried by a block 42 slidable within a housing 43. There is a spring 47 between flanges 44, 45 within the housing. The plunger 41 reciprocates in a cylinder 48 in the pump body 43 which is attached to the housing 30 by means of a nut 49. The outer end of the cylinder 48 carries a disc 57 which under centrifugal force rests on a seating 58 and closes the suction to an inlet port 59. This latter has screw-threaded member 60 which acts as a retainer for a disc 61 formed with a conduit communicating with a discharge valve 62 for the delivery pipe 64. The block 42 contains a slide 65 which is coupled by a rod 67 to an eccentric strap 70'of a sleeve 71 carried by a shaft 72, which at its rear end is splined at 51 to a tubular shaft 40 passing through the hollow shaft 24 and which is adapted to be rotated at a speed different from the speed of the air-screw or to be held stationary. Between the two pumps the strap 70 is formed with a fork 52 engaging a roll 53 rotatable on a fixed axle 54 supported between two diaphragms 74, 75. Two other pumps similarly driven by an eccentric strap 71a are disposed at 180‹ to the first two. Within the cap 33 is a governor casing 76, the spindle 81 of the governor being passed through a casing 84 and its grooved feeds to the pipe system are controlled by lands upon the spindle. The pump casing 30 and the cap 33 are partially filled with oil which when the air-screw is rotating, finds its way to the interior of the cap 50 of each pump. During the intake stroke of the pump, the disc 57 is sucked up. and oil enters the cylinder 48, the suction being aided by centrifugal force which holds the ball 62 on its seat. On the delivery stroke oil passes the ball 62 and is discharged along the pipe 90 to the union 87 on the casing 84. The pipes 98 and 95 lead to two sets of pressure cylinders according to the position of the control spindle 81. Pressure cylinders carried by the block 28 accommodate rams 104, 204, 304, which press against the flange 21 when liquid under pressure is admitted to the left-hand end of the cylinders. The block 28 also contains 6 rams 110, 111, 210, 211, 310, 311 which press against the left-hand flange 20 of the sleeve 19. According as the speed rises or falls above or below the desired speed, so the governor moves the control valve to admit pressure to the three rams to increase pitch, or to the six rams to diminish pitch accordingly. In an alternative form of pump the block 42 is connected by a link 282 to a pivoted lever 284, the outer end 286 of which contacts with a cam 288. In operation, centrifugal force on the block 42 moves the plunger 41 outwardly on its delivery stroke. The return is effected by the cam and when centrifugal force and pressure are balanced, the plunger 41 is held just clear of the cam which then rotates idly. In a modification, the cylinder blocks are axially spaced and the rams are formed coaxially with their free ends abutting against projections from the sleeve which carry the sliding blocks of the eccentric pins. In order that the control shaft 81 may be moved by hand to over-ride the governor, the end block 85 of the governor has in contact therewith a rod 292 which passes through the hollow shaft 72 and its hollow driving shaft 40 to a piston 287 housed within a cylinder 288 which is suitably connected to the hollow shaft 40, and at its outer end this cylinder 288 is continued and coupled to the means 216 for driving the pump. Ports 214 at the end of the cylinder 288 are provided whereby pressure under hand control, admitted through a port 218, may force the piston 287 against the spring 219 and so move the rod 292 for the purpose of moving the control valve 81.