GB581327A - Improvements in variable pitch airscrew control mechanism - Google Patents

Abstract

581,327. Fluid-pressure servomotorcontrol systems. DE HAVILLAND AIRCRAFT CO., Ltd., GILLMORE, K. B.,'DOVE, E. B., and GOURLAY, G. K. L. Nov. 24, 1942, No. 16664. [Class 135] Variable pitch airscrew control mechanism of the kind in which a progressively-operating powerdriven pitch-changing mechanism is set in motion to initiate a change of pitch and is stopped when the desired pitch is obtained includes a servo - device operated by liquid pressure for setting in motion and stopping the pitch-changing mechanism and means under manual control whereby the operator can select any one of a number of definite blade pitches. As shown in the Figures, a pitch-changing shaft 64 is rotated in one direction or the other by bevel gearing selectively clutched to an engine-driven shaft by hydraulically - actuated clutches 56, 58. These clutches are controlled by a piston valve 10 working in a ported follow-up sleeve 12, reciprocated by screw- and-nut mechanism 23, connected by worm gearing 231 and bevel gearing 21 with the shaft 64. The valve 10 is actuated against the action of a spring 24 by fluid pressure delivered through a pipe 26 connected to a manually-operated multi-way piston valve actuated by a knob 90 provided with a pointer co-operating with a scale having five graduations marked respectively " Landing brake," Dive brake," " Constant speed," " Unbraking " and " Feathering." In the position shown, which is the feathering position, the pipe 26 is connected to exhaust through a groove 84, while a pipe 80 leading to the control valve 70 for constant speed unit 62, a pipe 76 leading to a power cylinder operatively coupled to the engine throttle and a pipe 78 supplying fluid under pressure are blanked off. In the constant speed position, the pipes 26, 80 are connected by a passage 88, and the pipe 76 is connected to exhaust. In the braking position, the pipes 76 and 80 are connected to put the throttle under the control of the constant speed unit and the pipes 26, 78 are coupled to move the valve 10 towards the braking position. To arrest the valve 10 when it has reached the desired position it is provided with a spindle 18 formed with a rack 94 engaging a pinion on a shaft 98 mounted in ball bearings and carrying a collar 116 with two diametrically opposed projections 118, 120 adapted to co-operate with stop rings 106, 108, 112 and 114. These rings have serrated outer edges and are held in the desired position in a non-rotatable casing 104 secured to the valve 72 by a spring-ring 99. The collar 116 is splined to the shaft 98 and is held in its normal position by opposed springs 134, 136 so that it can move axially in the event of it fouling a stop during adjustment. To hold the valve 10 against movement, the shaft 98 carries a disc 122 with a friction lining 124 adapted to be engaged by a plate 126 held against rotation and reciprocated by an externally screwed boss 128 engaging a non- reciprocating nut rotatable by means of a lever 132. A cam or linkage may be interposed in the connection between the airscrew blades and the follow-up sleeve. Specifications 563,212 and 581,326 are referred to.