Pitch change control system

Claim 1

A pitch change actuation system for adjusting the pitch of a variable pitch propeller blade rotatably mounted to a hub of a propeller, said pitch change actuation system having a pitch change actuator operatively connected to the propeller blade and a control valve means operatively connected to the pitch change actuator for selectively pressuring the pitch change actuator to effectuate a desired change in the pitch of the propeller blade, characterized in that said pitch change actuator comprises: (a) an annular blade actuation piston operatively connected to the propeller blade whereby longitudinal movement of said blade actuation piston effectuates a rotation of the propeller blade thereby resulting in a change in the pitch of the propeller blade, said blade actuation piston having an outwardly extending head member and an annular shaft longitudinally extending therefrom operatively connected at one end to the propeller blade; (b) a second annular piston having an annular head member and a longitudinally directed annular shaft extending therefrom disposed in spaced relationship about the shaft of said blade actuation piston; (c) spring means operatively disposed between said second piston and said blade actuation piston for exerting a preload force against said second piston so as to bias said second piston away from said blade actuation until the preload force is overcome; (d) pitchlock means operatively interconnected between said second piston and said blade actuation piston for restraining inadvertent blade pitch reduction; and (e) conduit means operatively interconnected in fluid communication between said control valve means and said pitch change actuator for selectively directing a pressurizing fluid between said control valve means and said blade actuation piston thereby providing a first pressure force on said blade actuation piston and between said control valve means and said second piston thereby providing a second pressure force on said second piston.