Patent GB-810453-A (GB)
Title: Improved variable pitch propeller control system
IPC: B64C11/42
Filed: 1957-02-27
Abstract: 810,453. Variable pitch propellers. GENERAL MOTORS CORPORATION. Feb. 27 1957, [March 19, 1956], No. 6569/57. Class 114. The low pitch stop of a propeller, having a governor which varies its pitch to keep the speed constant, is variable during propeller operation so as to be set at a blade angle slightly below that required for normal governed speed during take-off constant speed operation. A gas turbine 90, Fig. 8, drives the propeller through a reduction gear 92 and is conjointly controlled with the propeller pitch. The blades 22, Fig. 1, twist in sockets 21 in a hub 20 surrounded forwardly by a spinner 75 having an open nose 76 leading to cooling fins 82, Fig. 7, in a feathering pump and reservoir assembly 55. At the rear of the hub, a housing 25, Fig. 1, and cover 26 enclose another reservoir for hydraulic fluid for activating the pitch changing mechanisms and accessories thereto. Within the reservoir are disposed pumps 36, Fig. 6, one of each blade, actuated by the rotation of the propeller, and assemblies 30 ... 33 of speed governor valves, feathering valves, a solenoid valve and pitch stop and pitch lock valves. Each assembly is mounted beneath a removable access plate 42 to permit its removal or adjustment without dismantling other mechanisms. Liquid cooled in the reservoir 55, Fig. 7, flows through a pipe 81 to the main reservoir which drains into the reservoir 55. Within the rotating reservoir, a member 28, Fig. 5, carrying a sleeve 145 is held against rotation by being anchored to the casing of the speed reduction gear 92 and on the sleeve there slide three control rings 150-152, Figs. 5 and 9, which actuate respectively the valves controlling feathering, or speed sensitive valve element and the speed setting. These rings move upon rotation of toothed rings 137, 136 and 142 by levers 96, 95 and 97 respectively. The teeth on the ring 136 are discontinuous to move the ring 151 at certain settings only of the lever 95. An electric motor actuates the speed lever 97 which through movement of the speed ring 152 actuates a cam lever 266 to displace a rod 265 which rocks a lever 263 to move a piston 260 engaging a governor spring 225 to adjust its tension, the operation being aided by low pressure fluid behind the piston. To maintain the set speed, a valve element 209 urged upwardly by centrifugal force and downwardly by the governor spring 225 acting on a speed sensitive lever 223 pivoted at one end to the end of the rod of the valve element 209 maintains its position, downward movement due to decreased speed being rectified by a land 221 on the element uncovering a port 220 in a follow up sleeve 210 to admit low pressure fluid beneath a differential piston or distributor valve 213 to raise the piston and rock a lever 212 connected thereto whose other end moves the sleeve 210 to block the port again. On an increase in speed the land 221 rises and the underside of the differential piston 213 so connected to drain. The differential piston is rendered more sensitive by a jitter valve 228, 229 and controls the admission of fluid to the pitch change chambers in the propeller hub except when feathering. The ring 151 carries a shoe 286 to which is pivoted a lever 287 supporting a nut 288 on a screwed rod 290 rotatable by a master gear 197, which engages toothed sectors on the blades to coordinate their pitch change movements, only when that gear is in the beta range, i.e. when the pitch is between -7 degrees and- + 32 degrees. When the pilot's control lever 108, Fig. 8, moves into this range, it moves the control ring 151 to the left and the lever 287 raises the speed lever 223 and governor valve 209 and reduces the pitch, the master gear 197 rotating the screwed rod 290. High pressure fluid flows from each pump 36 through conduits 170, 173 to a spool valve 165 in the feathering valve assembly 31 which normally provides a through passage to a passage 180 leading to conduits 233 and 235 in the governor valve assembly 30. A valve 192 in this assembly leads to a lowpressure fluid supply. The distributor valve 213, by its lands 215, 216 keeps a port 246 slightly open to the passage 235 to maintain sufficient pressure in the blade hub through a conduit 247, a space between lands 177, 178 on the spool valve 165 and a conduit 250 to oppose natural twisting of the blade. Increased speed actuates the control valve 209 to move the distributor valve 213 downwards and increase the flow of fluid, increased pitch resulting. Decreased speed opens the port 246 to drain and the blade twist and pressure fluid in the decrease pitch chamber 256 reduce the pitch. Pitch stops and pitch lock. When the speed lever 95 on the ring 136 is moved anticlockwise, displacing the control ring 151 to the left, Fig. 9, the ring turns on arm 274 rotating a control valve 277 in the pitch stop and pitch lock assembly 33 to supply low pressure fluid through a conduit 281 to a low pitch stop release chamber 282, and withdraw a low pitch stop. 195 from the path of a lug 317, Fig. 10, one of three lugs 316 .. 318 on the ring 136. On reverse movement, the stop is reinstated when the pitch angle is 20 degrees, the stop normally functioning at a pitch 2 degrees below this. At a pitch angle of 20 degrees, the lever 287 on the shoe 286 on the control ring 151 engages a cam surface on the speed sensitive lever 223 to cut off the pressure fluid from the decrease pitch chamber of the hub and so stop pitch decrease. The lug 317 cannot normally move past a stop actuated by a manually controlled solenoid 134, Fig. 5, the stop being retracted to permit the ring to move into the beta control range. A pitch lock mechanism which permits increase but not decrease of pitch is controlled by a valve 272 in the pitch lock valve assembly 33, normally connecting the low pressure fluid supply to the chamber 196 of the mechanism. If the propeller overruns by say, 5 per cent. a speed sensitive valve 273 lifts and connects to drain a passage 321 leading from the chamber 202 above the pitch lock valve 272 which then connects to drain the fluid passage 323 leading to the chamber 196, permitting the pitch lock to engage the master gear 197. The pilots control lever 108, Fig. 8, operates from a slot 113 corresponding to beta range control through a flight idle position at a gate 115 and a cruise range 112, where the governor control operates to a take-off position TO adjacent which is a small range of manual control. A manual switch 116 if moved into a position F is the normal control of feathering, the switch energising the motor 58, Fig. 7, and a solenoid 118, Fig. 8, to rock the lever 96 on the ring 137 to displace the feathering control ring 150, Fig. 9. The switch also actuates the feathering pump for a predetermined period. The motor may be used to adjust the blade pitch when the propeller is stationary. After the motor 58 has started, the feathering pump is not connected to the hub passage 172 until the pressure of the pump 36 is a predetermined amount less than that of the feathering pump whose pressure is limited to 3000 lbs./sq. in. In emergency, depression of a lever 107, Fig. 8, simultaneously feathers the blades and cuts off the fuel supply, the latter by actuating the lever 95 or the ring 136 connected to the speed control ring 151. This ring moves to the right, Fig. 9, drawing with it a cam 370 which engages rollers 362, Fig. 13, on one branch of a forked end of the rod 351 of a feathering control valve 350. A roller on the other arm of the fork engages a cam 363 of opposite slope secured to the feathering control ring 150. The control rings 151, 150 thus operate the valve 350 jointly but either may do this independently of the other. The valve controls movement of the spool valve 165 which then interrupts connection between the distributor valve 213 and the increase pitch chamber to disable the governor, connects this chamber to the high pressure fluid supply and opens the pitch decrease chamber to drain the ring 150, which is pushed to the left as the feathering ring 137 is rotated clockwise by the lever 96, is actuated by a negative torque sensing device, this device also being adapted to prevent feathering during landing. Should this cam-actuated mechanism fail, the mechanical connection of the emergency feathering control lever 107, Fig. 8, through a link 105, coordinating control 102, links 101, 100 and the lever 95 is adequate to effect feathering. An hydraulic pump housed in the feathering reservoir 55 and driven by an electric motor provides power for feathering. Specifications 711,945 [Group XXXV], 724,855, 779,116, 781,368, 810,454, and 810,455 are referred to.