Patent GB-821414-A (GB)
Title: Variable pitch propellers
IPC: B64C11/30
Filed: 1956-05-15
Abstract: 821,414. Variable pitch propellers. UNITED AIRCRAFT CORPORATION. May 15, 1956 [May 17, 1955], No. 15079/56. Class 114. A variable pitch propeller has a servomotor for varying the pitch of the blades and a governor and a distributer valve operatively connected to the governor for controlling said servomotor, means for moving said distributer valve including a servo system, and a feed-back connection between said servomotor and said governor and distributer valve. In an embodiment, suitable for use with an aircraft gas turbine engine, a power lever, which also controls a fuel regulator, is connected to a pulley 40 by which a shaft 52 is rotated through gearing 44, 46, a shaft 48, and gearing 50 whilst a condition lever is connected to a pulley 42 which rotates a shaft 64. A speed setting cam 54 on the shaft 52 coacts with a follower 74 on a bell-crank lever 76 pivoted at 78 and engaging at 82 with an arm 84 which is connected at 86 with a lever 88 and a control valve 92. The right-hand end of the lever 88 carries a roller 90 which bears against an abutment for the loading spring 102 of a governor by which a control valve 104 is operated. Adjustment of the valve 92 by the cam 54 results in movement of a servo-piston 98 which, through an arm 100, terminating at the roller 90 causes the compression of the spring 102 to be varied, the lever 88 transmitting a follow-up movement back to the valve 92. The valve 104 has an inlet 146 for fluid under pressure and two outlets 148, 254 which lead to a reversing valve 156 having a pair of lands so arranged as to blank off one of the two outlets from the valve 104 whilst connecting the other to a conduit 158 leading to the servomotor 106 which actuates the pitch-varying mechanism of the propeller. The servomotor 106 consists of a fixed piston 108 and a moving cylinder connected to a rack 120 which meshes with a pinion 122 which may be connected to the propeller control valve. The servo-cylinder 106 carries a cam 164 which coacts with a follower 170 on a bell-crank lever pivoted at 172, the other end of the bell-crank lever engaging an arm 176 connected at 138 to the lever 100 and engaging at its other end with an anticipator cam 56. The arrangement is such that when, e.g. an increased speed is selected, resulting in a compression of the speeder spring 102, the consequent movement of the servocylinder 106 causes the cam 164 to allow the bell-crank lever pivoted at 172 to move in a clockwise direction thereby relaxing the compression of the spring 102 through the arm 176 and lever 100. The consequent upward movement of the valve 92 causes a further adjustment of the servo-piston 98 to apply further compression to the spring 102. A rotating chopper valve 134 is interposed between the valve 92 and the servo-piston 98 to increase the time constant of the system. At the same time as the shaft 52 is rotated to select and increased speed setting the anticipator cam 56 is operated to cause the arm 176 and lever 100 to relax the compression of the spring 102 but the resultant movement of the valve 92 causes the servopiston 98 to wipe out the anticipation signal. Variable stops for positive or negative pitch operation are provided and their settings are determined by high and low pitch stop cams 60, 62 respectively with which followers 190, 192 carried respectively by arms 194, 196 are co-operable. The arms 194, 196 are connected at their other ends to rods 214, 216 which engage a lever 218 pivoted at 220 and engaging the valve 104. Intermediate points on the arms 194, 196 carry follower rollers 198, 200 for cooperation with cams 168, 166 and are connected to pistons 206, 208 which are under the control of the reversing valve 156. The arrangement is such that, depending upon the position of the reversing valve, one of the pistons 206, 208 is depressed to cause its follower to engage the corresponding cam while the other piston is raised to withdraw the corresponding follower from its cam. The reversing valve 156, which also reverses the effect of the valve 104 on the servomotor 106, is actuated through a link 262 and lever 264 by a cam 58 which has a snap action device whereby the valve 156 is moved rapidly when the main power lever is moved from the positive to the reverse range of propeller operation and vice versa. Feathering and unfeathering cams 70, 68 are rotated by the shaft 64, the feathering cam coacting with a tappet 300 which is connected through a bellcrank lever 302 and a rod 304 with a feathering valve 152 which, when raised, causes the servocylinder to move to the feathered position by venting the conduit 158 through passages 308, 310, 312. Unfeathering of the propeller is effected through the cam 68 which engages a follower 69 to impart a large deflection to the valve 104 through the arm 196, the rod 216, and lever 218. Feathering may also be effected by a solenoid valve 320 which admits fluid under pressure to an annular space 332 to raise the feathering valve. The feathering valve may also be raised to feather the propeller in the event of loss of power by a member 346 connected to an engine torque-sensing device. In some installations it may be desirable to unfeather the propeller such that it is rotated at a given speed and for this purpose a cam 66 rotated by the shaft 64 is provided. This cam overrides the cam 54 by deflecting the bellcrank lever 76 to apply a low speed setting to the governor spring 102. An electrically controlled valve 380 may be provided for synchronizing two or more power plants, the valve 380 applying pressure to a chamber 386 in the valve 104 to bias the latter. In a modification, the mechanism between the control shaft 52 and the speeder spring 102 of the governor is simplified and a pitch stop valve is interposed between the reversing valve and the governor actuated valve and operated by cams on the moving cylinder of the main servomotor. This arrangement takes the place of the cams 166, 168 and the linkages 194, 196 &c., leading back to the valve 104. Also in the modification, synchronization is effected by electrical signal generators driven by each engine and whose outputs are compared and the resulting signal applied to a valve which controls a fluid pressure acting on the governor actuated valve. Specification 781,961 [Group XXIX] and 821,415 are referred to.