Patent GB-821415-A (GB)
Title: Variable pitch propellers
IPC: B64C11/38
Filed: 1956-05-15
Abstract: 821,415. Variable pitch propellers. UNITED AIRCRAFT CORPORATION. May 15, 1956 [May 17, 1955], No. 15080/56. Class 114. In a propeller having variable pitch blades, a servomotor for varying the pitch of the blades through positive and negative ranges and mechanical stops defining extreme positive and negative pitch positions, a governor and distributer valve for the servometer are provided together with manually operated means operatively connected to the pitch-varying means for providing a variable pitch stop in the intermediate range between the mechanical stops. A power lever 34 actuates a fuel control device 20 responsive also to the air inlet temperature of a compressor 12 forming part of a gas turbine 10 which drives a variable pitch propellor 18, the control 20 being also responsive through a line 28 to the speed of the compressor and to its exhaust pressure through a line 30. The pitch control device 36 includes a motor cylinder 106, Fig. 2, displaceable about a fixed piston 108 when one side 110 thereof is opened to high pressure or drain pressure through a passage 118, the other side 112 being maintained at constant pressure. The power lever 34 rotates a pulley 40 connected through gears 44, 46 and 50 with a shaft 52 carrying a speed setting cam 54, anticipator cam 56, reverse governing switch over cam 58, high pitch stop cam 60 and low pitch stop cam 62. The speed setting cam 54 rocks a bell-crank lever 76 of which the second arm 80 engages a rod 84 having its end 86 pivoted to a rod 88 carrying at its remote end a roller 90 bearing on the spring 102 of a speed governor associated with a distributer valve 104. The pivot 86 is connected to the piston of a speed setting pilot valve 92. On movement to increase speed, the arm 80 rises permitting high pressure fluid acting continuously beneath the piston of the piston of the pilot valve 92 to raise the rod 84 and its pivot 86, permitting pressure fluid to flow to a speed setting motor 96 adapted to rock a lever 100, of which the other end is pivoted to the roller 90, to depress the governor spring 102. The connection from the pilot valve 92 is through a line 132, an intermittently acting rotating "chopper" valve 134 and a line 136, the "chopper" valve serving to lengthen the time taken to adjust the speed change. Under these conditions, high pressure fluid flows from a pump 114 through a line 150, a feathering valve 152, lines 154, 146, the distributing valve 104, line 148, a reversing valve 156 and lines 158, 118 to the pitch changing motor cylinder 106. As the cylinder 106 moves, a cam on an arm 162 fixed to the cylinder allows a roller 170 and a bell-crank lever to move slightly downwards lifting a roller 174 at the other end of the lever clear of a rod 176 fixed to the lever 100 at its pivot 138 ; the lever 100 turns anticlockwise raising the roller 90 and easing the tension of the governor spring 102. The upward movement of the roller 90 rocks the rods 88, 84 about the arm 80, their pivot 86 rises and the pilot valve 92 opens the passage to the speed setting motor 96 which turns the lever 100 clockwise and restores the roller 90 and spring 102 to their normal positions. Simultaneously the rods 84, 88 move the pivot 86 and piston of the pilot valve 92 downwards to their normal positions. To cancel the decrease pitch signal normally accompanying the movement for increased speed, the anticipatory cam 56 lowers the rod 176 about its pivot 138 rocking the lever 100 anti-clockwise to annul the normal downward movement of the roller 90. High and low pitch stops. The power lever 34 rotates high and low pitch stop cams 60, 62 on the shaft 52, the cams rocking beams 194, 196 connected by rods 214, 216 to a rocking lever 218 to displace the distributer valve 104 to increase the pitch. The beams rock about rollers 198, 200 which support cross connected piston valves 206, 208 adapted to ensure that one cam only is operated by its associated cam 168, 166 on the arm 162 of the moving cylinder 106. Both stops act to prevent the pitch from varying towards zero pitch, the high pitch stop being in the negative pitch range and being brought into action by the reversing valve 156. Reversing. As shown, the distributing valve 104 connects the high pressure line 146 with the line 148 leading to the reversing valve 156. Upward movement of the distributing valve 104 connects the line 146 with a line 254 which opens into a reversing valve 156 to connect with the high pressure line 158 when the reversing valve 156 is moved upwards. This movement also opens a line to the pistons 206, 208 and effects change over of the pitch stop cams, engaging the roller 198 with the cam 168. The valve 156 moves rapidly under control of a snap action cam, the reverse governing switch over cam 58, which comprises opposed springs 270 and a detent 272. Feathering. Rotation of a condition lever 38 and pulley 42 actuates the feathering cam 70 to displace to the right a rod 300 connected by a bell crank 302 and rod 304 to the stem 306 of the feathering valve 152. This raises the valve to open a line 308 branched from the line 158, 118 to drain via passages 310, 312 in the valve : the cylinder 106 moves to the right and increases the pitch. Alternatively, a solenoid valve 320 may admit high pressure fluid from the line 150 to a chamber 322 in the feathering valve 152 to raise the valve or it may be raised by external mechanism, operable on loss of power in the power unit, which raises a stem 340 resiliently connected to the valve stem 306. The feathering valve cam does not actuate the valve until the condition lever has almost reached the " feathered " position. Up to this point it carries with it the unfeathering cam 68 which engages the beam 196, frees the low pitch stop and rocks the beam to lift the distributer valve and create an artificial " increase pitch " condition. The condition lever 38 may actuate a speed depression cam 66 which engages the bell crank lever 76 to override the speed setting setting cam 54 and relieve pressure on the governor spring 102 simultaneously with lifting action of the unfeathering cam 68. On unfeathering, the speed depressing cam sets the governor spring 102 to determine the speed before the speed setting cam 54 takes over. Synchronous controls. When two or more power plants operate together a synchronising device 380, may apply variable pressure to a chamber 386 beneath the distributer valve 104, the pressure being determined by a spring biased tongue or flapper element 392, Fig. 4, disposed opposite a nozzle 394 supplied through a line 382 from the high pressure line 150, the pressure-adjusted fluid discharging through a line 384 to the chamber 386. A proportional solenoid 390 actuates the tongue 394. Specifications 600,045 [Group XIX], 636,402, 781,961 [Group XXIX], 821,414 and U.S.A. Specification 2,579,723 are referred to.