GB846811A - Variable pitch propeller - Google Patents

Abstract

846,811. Variable pitch propellers. UNITED AIRCRAFT CORPORATION. Oct. 22, 1958 [Nov. 27, 1957], No. 33754/58. Class 114. A propeller comprises means to increase or decrease blade pitch, locking means responsive to propeller overspeed to prevent blade pitch decrease and means to disable the locking means when the blades are increasing in pitch. The pitch change motor 20 comprises a cylinder 22 and a piston 24 having cam rollers 26 engaging stationary and rotary cam slot members 28, 30, the latter having a gear ring 32 Figs. 1 and 2, in mesh with a ring 34 carried by the propeller blades 14 so that movement of the piston 24 causes rotation of the blades 14 about axis 18. The pitch lock unit comprises a stationary member 42 and rotary member 44 having cooperating teeth. During normal engine and propeller operation, pressure fluid used in the pitch change motor 20 is also introduced to chamber 40 to move piston 45 which takes member 44 out of engagement with member 42 and thus disables the locking means. Loss of pressure in chamber 40 allows springs 54 to engage members 44 and 42. During normal operation said pressure fluid also enters cavity 60, line 62 and chamber 64, Fig. 3, surrounding disarming valve 66, thence via port 74, annular chamber 76, port 78 and annular chamber 80 to line 82 leading to overspeed flyball chamber 84, said pressure fluid also being directed through chamber 86 and line 88 into chamber 90 so that sliding value 48 is in hydraulic balance. During overspeed conditions flyballs 46 are flung outwardly to overcome force of spring 94 and move valve 48 to the left to drain fluid in chamber 40 through line 50 and annulus 52 thereby permitting springs 54 to engage the pitch lock members. When propeller blades are moving to a higher pitch, skirt 98 carried by the pitch change motor piston 24 moves to the right with respect to stationary sleeve 100 to increase the volume of cavity 75 and reduce the pressure therein, thereby reducing pressure in line 73 and cavity 71 to cause a pressure differential across the disarming valve 66, the piston 68 of which is moved to the left against its spring 72 so as to intially cause land 108 to block off port 74 thereby preventing flow of pressure fluid from chamber 64 to chamber 84. This initial movement of valve 66 also puts annular chamber 76 into direct communication with cavity 71 thereby placing chamber 84 in communication with cavity 75 and thus reducing the pressure in chamber 84. The resultant pressure differential on sliding value 48, in combination with the force of spring 94, is such that flyballs 46 are no longer able to move value 48 to the left to bleed cavity 40 to permit engaging of the pitch lock members, hence the pitch lock is disabled at all times while the propeller blades are increasng in pitch. Further movement of valve 66 to the left enables it to serve as a pressure regulating valve for the pressure in chamber 84. Specifications 514,725, 526,100, 724,284, 754,095 and 777,572 are referred to.