Patent GB-656050-A (GB)
Title: Improvements relating to helicopters
IPC: B64C27/30
Filed: 1948-12-30
Abstract: 656,050. Helicopters. PENNINE AIRCRAFT, Ltd., and NEALE, J. S. Dec. 30, 1948, No. 33486. [Class 4] [Also in Group XXIX] A helicopter, in which a pumping system driven by the engine maintains a pressure in a hydraulic pitch control system, is provided with means responsive to variations in lift of the rotor for actuating the engine controls to correct such variations. Each rotor blade, the mounting and drive for which is described later, is rotated for pitch change about its longitudinal axis by an arm m, Fig. 3, attached thereto and coupled to a piston n in a cylinder o connected by pipes t and u to the suction and delivery sides of a gear pump v located in the rotor head in the manner described in Specifications 605,561 and 647,744. The pump v is supplied with liquid from a further engine driven pump y, the delivery pressure of which is controlled by an adjustable overflow valve 28 by means of which the pilot may vary the collective pitch of the blades. In order to maintain the lift at a predetermined value, a restriction 35 is provided in the pipe from pump y to pump v and a cylinder 36 is connected across the restriction. Collective movement of the pistons n in either direction under the influence of a variation of loading conditions in the rotor disc will create an increase or reduction of pressure in the pipe 30. This will create differential pressures across the restriction 35 which will cause a servo-piston 37 to be displaced in its cylinder to actuate the engine throttle in the appropriate direction to correct the lift to its normal value. To ensure emergency pitch control in the event of an engine failure the pump v may be connected to a hand pump 32 instead of the pump y by means of a two-way valve 33 actuated by a snap switch 31. The switch is held in the position in which the valve 33 passes liquid from the pump y by a piston 40 supplied with pressure liquid from a pipe 38 so that when an engine failure occurs loss of pressure behind the piston 40 allows the spring 41 to move the switch to the position in which the valve 33 passes liquid from the hand pump 32. A pin stop 34 is provided to lock the system in the emergency position. The root of each blade a, Fig. 2, is mounted in a member d by ball-bearings b separated by springs c. The member d is supported in the rotor head e by means of a stiff bonded rubber sleeve f and a ball g secured to the member d is engaged by a spherically-seated spring-loaded member i provided with a rubber liner h. A stop k prevents rotation of the ball about the blade axis. The rotor head is formed with a spherical socket adapted to fit over a ball 7 on the top of the rotor shaft x, the head and the shaft being interconnected by a plurality of rods 8 pivotally attached to the head e and embedded in rubber blocks 9 fixed in sockets 9a carried by arms on the shaft x. The lower ends of the rods 8 are attached to a rotating ring 10 which rides on a fixed ring 11 which in turn is connected by rods 12 to pistons 13 in cylinders 14 connected by pipes 14a to a similarlyarranged system in the pilot's cockpit to enable the pilot to control the inclination of the rotor head. The shaft x which runs on bearings 15, is driven through bevel gears 16, 17 and a disc clutch 18 from a shaft 19. The clutch 18 is engaged by application of pressure, through ball-bearings 20, from pistons 21 in cylinders 22. Springs 23 release the clutch when the fluidpressure drops. The shaft 19 is coupled to the clutch driving element by rubber blocks 24, with a ball-joint 25 to restrict whirling of the shaft.