GB854530A - Improvements relating to variable pitch propellers - Google Patents

Abstract

854,530. Variable pitch propellers. UNITED AIRCRAFT CORPORATION. Oct. 22, 1958 [Oct. 22, 1957], No. 33857/58. Class 114. In a variable pitch propeller the means for changing the pitch of the blades is regulated by a governor responsive to functions of propeller speed and acceleration. A pump supplies fluid via line 42 to a governor 24 thence via low and high pitch lines 58, 60 to a pitch change motor. The governor comprises a flyweight unit 30 rotating with the propeller to act on a pilot valve 36 in opposition to the force of a spring 38, and a pitch change valve 40. When the propeller rotates in an underspeed condition spring 38 overcomes forces of flyweight 30 and moves pilot valve 36 upwardly. Pressurized fluid acts through pump line 42 annulus 44, ports 46, annulus 68, line 70 and annulus 66 on surface 64 to lift valve 40 which places line 42 into communication with low pitch line 58 to cause the motor to decrease the pitch of the blades. Thus in a propeller underspeed condition valve 36 and hence valve 40 move upwardly at a velocity proportional to propeller acceleration, thereby reducing the volume of a chamber 74 between stationary wall 76 and skirt 78 of valve 40 and causing fluid to be forced through a restriction 82, the pressure drop across this restriction thus being proportional to propeller acceleration and acting through sump line 72, annulus 86, ports 88 and 90 to chamber 84, the pressure fluid in chamber 74 acting via aperture 87 and chamber 85 to apply a lifting force on valve 36 proportional to the propeller acceleration. When the propeller rotates in an overspeed condition, flyweights 30 move outwardly to force valve 36 downwardly. Pressure fluid flows via annulus 44, port 46, annulus 48, aperture 50, annuli 52, 54 and 56 to act on surface 62. Area of surface 62 is a proportion preferably one half, of that of surface 64. Pressure in annulus 66 is bled through annulus 68 to sump line 72, and valve 40 is therefore moved downwards with the pilot valve 36. The volume of chamber 74 increases at a rate proportional to the velocity of valve 36 and hence the acceleration of the propeller. This reduces the pressure in chamber 74, aperture 87 and chamber 85, causing an inflow from line 72 through the restriction 82 so that a force acts in annulus 56 proportional to propeller velocity to move valve 36 downwards. For emergency propeller feathering purposes, fluid may be passed through line 102 into chamber 104 to move valve 40 downwardly. Specifications 514,725, 526,100, 683,906, 754,095 and 777,572 are referred to.