GB544570A - Improvements relating to variable-pitch airscrews - Google Patents

Abstract

544,570. Screw propellers. ABSALOM, K. C. March 15, 1941, No. 3577. [Class 114] Variable-pitch mechanism for a propeller or airscrew is driven by a shaft 11 which extends through the propeller-shaft and is geared to the blade-roots by bevel or other gearing, selectively-clutchable free gears 28, 32 on the shaft being driven in opposite directions by the propeller-shaft. When both gears are free, the shafts are coupled to rotate in unison. In one construction, the gears 28 and 32 are driven through intermediate gears 23 and 29, 30 by an annulus 20 on the propeller-shaft, and are provided with hydraulically-operated clutch-shoes 34. Hydraulically-operated clutch-shoes 38 cooperate with the annulus to couple the shafts. The clutch-shoes are controlled by a unit 41 comprising a valve 40 connected to a centrifugal governor 47, a plunger-valve 59, and a booster-pump 55. Normally, the clutch 38 is applied, and the shafts rotate in unison. If, however, the engine-speed increases, the valve 40 moves towards the right, pressure is transmitted through a line 45, the gear 28 is clutched, and the pitch is coarsened. Simultaneously, the valve 59 is moved towards the left, a line 43 is put to exhaust through a line 44, and the clutch 34 is released. Similarly, if the engine-speed decreases, the valves 40, 59 are moved towards the-left and right, the clutch 34 is released, the gear 32 is clutched, and the pitch is reduced.. For feathering or unfeathering, a control-handle 52, geared to the stop 50 of the governor-spring 48, is moved backwards or forwards, and power is supplied to the system by an additional booster-pump driven by an electro motor. When contra-rotating propellers are employed, the blades are connected by linkage.