Patent GB-553554-A (GB)
Title: Improvements in or relating to propeller pitch changing mechanism
IPC: B64C11/42
Filed: 1941-11-24
Abstract: 553,554. Screw propellers. UNITED AIRCRAFT CORPORATION. Nov. 24, 1941, No. 15142. Convention date, Dec. 19, 1940. [Class 114] Propeller pitch changging mechanism comprises a pair of hydraulic couplings and a control member which, when moved to either side of a neutral position retards the movement of the rotating member of the respective coupling thereby actuating mechanism for turning the blades on their axes, one coupling causing increase and the other decrease of the pitch. The blade roots are each provided with a worm-wheel 44 engaged by a worm 46 actuated by gears 60 from a shaft 62 carrying a gear 64 engaging externally and internally toothed rings 66, 68 concentric with the propeller shaft 12 and held together by a split ring 84 which permits relative rotation of the rings. The ring 66 is threaded on the propeller nut 16 which is keyed to the shaft 12, and forms a rotary quadrant portion 74 of a fluid coupling 75, the other portions of this coupling consisting of a fixed member 80 and one side of a laterally movable control member 82. A second fluid coupling 86 is formed by the other side of the control member 82, a fixed portion 94 and the outer quadrant portion 88 of the ring 68. The quadrants 74, 88 are provided with spaced vanes 76, 90 connected by a core member 78, 92 and the member 82 comprises a central portion 98, Fig. 4 connected by cross members 106 to curved walls 102, 104 thus forming two rows of passages for the flow of liquid. When the member 82 is in the neutral position shown in Fig. 1, both rows of passages are blocked by the peripheral surfaces of the parts 74, 88 and the smooth surfaces of the walls 102, 104 and of the parts 80, 94 offer little resistance to the fluid carried round by the vanes 76, 90 and the rings 66, 68 thus rotate in unison with the propeller. If the member 82 is moved to either side so that one row of passages is presented to the vanes 76 or 90, the flow of fluid through that coupling is retarded causing a retardation of ring 66 or 68. This results in a rotation of one ring relatively to the other and a consequent actuation of the shafts 62 and variation of the pitch of the blade. As the ring 66 is threaded on the hub 16, the relative rotation of the rings is accompanied by a movement longitudinally of the hub until the peripheral surfaces of the rings again cut off both rows of passages through the member 82. The position of the parts longitudinally of the hub thus give an indication of the pitch which may be shown on an indicator 156 by the provision of a plunger rod 150 connected to the indicator arm 154 and kept in engagement with the member 82 by, a spring 152. The non-rotating parts 80, 94 of the couplings are kept pressed towards each other by springs 160 engaging pins 158 carried by the fixed casing 110. The movements of the control member 82 are effected by fluid pressure and for this purpose the rim 96 of the member engages in a channel 112 in the casing to form annular chambers 114, 116 connected by conduits 118, 126 to a control valve 122, the controlling plunger 146 of which. is actuated in accordance with variations of the propeller speed by means of a governor 124. Exhaust passages 138, 140 in the valve lead by conduits 134, 136 to a reservoir in the casing 110 from which through a conduit 144, fluid is supplied to the valve by a rotary pump 130. The rise or fall of the plunger 146 due to speed variation thus connects one conduit 118 or 126 to the pressure fluid and the other one to the exhaust. Over-riding hand control to permit feathering of the blades is provided by a pump 164 and valve 162 which by conduits 166, 168 connected directly to the conduits 126, 118 through passages in the valve can apply pressure fluid to the chambers 114, 116 independently of the valve plunger 146. To enable feathering of the blades when the propeller is stationary, the member 82 may be rotated by an electric motor driving a worm 176 engaging teeth 108 on the rim 96 and the member is provided with lugs 180, 182 adapted, when the member is in either of its extreme positions to. engage motors 184, 186 in the core members 78, 92 and thus positively drive the respective ring 66, 68. The Specification, as open to inspection under Sect. 91, comprises also the arrangement shown diagramatically in Fig. 5, (Cancelled), in which each blade adjusting worm 192 carries a gear wheel 194 meshing with internally and externally toothed rings 198, 196 coaxial with the propeller shaft. The rings 196, 198 normally drive respectively rotary pumps 190, 188 which freely circulate fluid from a sump through suction pipes 206, 204 and delivery pipes 214, 208, 218, 216 through a governor controlled valve 210 which normally allows free passage of the fluid. If the speed varies. one pair of pipes 214, 218 or 208, 216 is blocked by the valve plunger 220 causing a retardation of the corresponding pump and a consequential relative movement of the rings 196, 198 and adjustment of the blades. This subjectmatter does not appear in the Specification as accepted.