GB820074A - Improvements in hydraulically actuated variable pitch propellers - Google Patents

Abstract

820,074. Variable-pitch propellers. UNITED AIRCRAFT CORPORATION. June 4, 1957 [June 14, 1956(2)], No. 17691/57. Class 114. In a variable-pitch propeller with mechanism for locking the blades against pitch change the outlet from a passage 42, for transferring oil to a chamber 44 in front of a pitchchange piston 18 to increase the propeller pitch, is closed by a centrifugally operated valve 64 when overspeed conditions arise the flyweights 62 of the centrifugal governor operating against a valve spring 74. Soon after this closure, a bleed valve 52, also centrifugally operated, cuts off communication between the chamber 44 and the corresponding chamber 46 behind the piston 18 to lock the pitch. The pressure fluid can leak behind the valve 52 to assist in its closure. To feather the blades, pressure oil is introduced into the passage 42 to open the valve 64 against the pressure of a pre-stressed spring 68 inside the spring 74. Should the pressure in the passage 42 recover of itself, the valve 64 opens and normal operation is resumed. Quick movement to the reverse position for braking can be effected by passing pressure oil from the chamber 46 behind the piston 18 through a slot 112 and port 114 to a chamber 116 behind a piston 110 adapted to displace a sleeve 92 to open the valve 64, the piston simultaneously withdrawing a wedge 98 from low pitch stops 100 to permit a flange 102 on the piston 18 to ride past them. Excess pressure building up behind the piston 18 in the chamber 46 is relieved by a surge valve 121 on the rear end of the passage 42, this valve which normally closes communication between passages 38, 40, leading from the low pitch and high pitch sides of the piston 18 respectively, being opened by the pressure acting on differential areas of a sleeve 122 constituting the valve. Specifications 607,856 and 766,621 are referred to.