GB1517167A - Control means suitable for a rotor blade - Google Patents

Abstract

1517167 Variable pitch propellers DOWTY ROTOL Ltd 1 Sept 1975 [24 Sept 1974] 41419/74 Heading B7V A control system for a variable pitch propeller comprises an actuator, e.g. a piston 16, urgeable in one direction by biasing means, e.g. spring 21 and counter weights 22, for adjusting the pitch in one sense, and subjectable to fluid pressure in a chamber 20 for movement in the opposite direction against the action of the biasing means, and stops 24 subjectable to the fluid pressure and maintained in an inoperative position when the pressure is above a predetermined value and being movable into an operative position to abut a shoulder 23 when the pressure falls below that value to arrest movement of the piston at a predetermined position, e.g. corresponding to 45 degrees pitch. In operation, if the pressure from a pump P and governor controlled valve V falls, piston 16 is moved by the biasing means against the falling pressure in chamber 20. Pressure is also relaxed on faces 28 of the stops 24 which allow them to be moved radially outwards by centrifugal force to engage the abutment 23. If the pressure falls due to failure of the engine E, as the propeller rotation reduces the centrifugal force will become less effective and the stops will be retracted by springs 27, allowing the piston to move to abut an end 30 of cylinder 18 which corresponds to a maximum feathered position of the blades and least drag on the aircraft to which they are fitted. In Fig. 2, not shown, the pump (114), reservoir (113), governor G<SP>1</SP> and control valve (V<SP>1</SP>) are all located within the propeller hub (112). The speed-responsive governor can be replaced or augmented by a positional control valve. The movement of the stops 24 can be controlled by electro-magnetic means, or independent fluid pressure pilot means, or by suitable mechanical means. The spring 21 can be replaced by a hydraulic device. The engine E can be of the reciprocating or rotary piston kind, or a gas turbine. The actuator can be of the rotary vane type.