Collective and cyclic in-mast pitch control system for a helicopter

Abstract

A compact, rugged, streamline, stiff, pitch control system is devised in a helicopter by concentrically nesting a cyclic pitch control tube and collective pitch control tube within the drive shaft and stationary mast of a helicopter rotor system. The collective pitch control tube terminates in an upper inclined flange which engages a stationary swashplate by means of a bearing member disposed in an inclined bearing raceway in the stationary swashplate. The stationary swashplate in turn is rotatably coupled through a universal joint to the cyclic pitch control tube. Relative rotation of the cyclic pitch control tube with respect to the collective pitch control tube adjusts the stationary swashplate to a selected inclination with respect to the longitudinal axis of the control tubes and of the helicopter mast. A rotating swashplate is rotatably coupled to the stationary swashplate and transmits the angular orientation of the stationary swashplate to the pitch case of each rotor blade as appropriate. The cyclic pitch control tube and collective pitch control tube are rotatably coupled to each other to permit relative angular rotation, but otherwise can be displaced vertically in the direction of the mast as a collective unit, thereby vertically displacing the stationary swashplate and hence the rotating swashplate to effect collective pitch control for all of the blades of the rotor system.