Patent GB-736248-A (GB)
Title: Improvements relating to contra-rotatable propellers
IPC: B64C11/30
Filed: 1953-05-04
Abstract: 736,248. Fluid-pressure servomotor-control systems. GENERAL MOTORS CORPORATION., May 4, 1953 [May 15, 1952], No. 12234/53. Class 135. [Also in Group XXXIII] In a contra-rotating variable pitch propeller assembly each propeller hub carries motors for adjusting the pitch of the respective blades, a regulator which includes pumps driven by the rotation of the hubs, control means which includes a follow up mechanism for controlling the adjustment of the pitch of the respective blades and means operatively connected with the control means of each hub for co-ordinating the control means in each hub to co-ordinate the adjustment of the pitch of the blades of the two hubs. Each hub includes a main and two auxiliary pumps, e.g. 62, 350, 352 rotating with the hub and driven by a stationary gear and pressure responsive valves, e.g. 216 for bringing the auxiliary pumps into circuit, an electrically driven feathering pump, e.g. 208, brought into operation by a centrifugal switch, and a distributing valve. The outboard distributing valve 201 is controlled on the one hand by a connection to the inboard regulating means and on the other by a follow up mechanism from the propeller blades. The connection to the inboard regulator comprises a shoe engaging a ring 51 which is connected through a gear train 10 including an anti-backlash device 98 to a master-shaft 82 in the inboard hub. The follow-up mechanism and the valve are connected through linkage 193, 197 to the ring 51 and the follow-up mechanism includes a cam slot 181 whereby a slight difference between the pitch setting of the outboard and inboard propellers occurs. The inboard distributing valve 200 and followup mechanism which also includes an anti-backlash device are connected through linkage 196, 192 to the master-shaft 82 which is also connected through linkage to a shoe 224 engaging a ring 48 which is connected to the pitch selecting means 58. In addition the inboard hub includes a speed governor which includes a valve 204 and a servomotor 570. The upper side of the servomotor 570 is connected by a pipe 700, a selector valve 438 and pipe 494 to the lower side of a piston 90 which is connected through linkage 98 to the master-shaft 82. The selector' valve 438 is controlled by a selector control valve 440 actuated from the pitch selector 58 by means of a member 518, to connect the pipes 700, 494 when the governor range is selected. The upper side of the piston 90 is connected to reduced pressure from a valve'202 which is also connected by pipe 432 to the valve 204. The valve 204 comprises a piston valve 608 slidable in a ported sleeve 604 slidable in a body 602. The valve 608 is connected to a spring loaded lever 654 pivoted at 656 on a fulcrum which is subjected to continuous vibration to prevent sticking, and is subjected to centrifugal force. The sleeve 604 is connected through linkage 690 to the servo motor piston 674. The lower part of the servo cylinder is connected by a pipe 664 to the valve 204 and the pipe 700 is branched at 666 to the valve 204. Fig. 11 represents the no speed error position of the governor. With an underspeed condition the valve 608 moves down connecting the lower side of the servo cylinder to exhaust and the servo piston 674 is moved down by pressure supplied by the piston 90 moving down under pressure on the upper side the sleeve 604 is thus moved down whereby the exhaust connection to the servo cylinder is broken and the pipe 666 is connected to the supply and also to exhaust via ports 618, 634; differential flow therefore takes place, the area of port 618 connected to exhaust being larger. Flow also continues from the lower side of piston 90 which moves down and thereby moves the valve 200 to supply pressure to the pitch change actuating cylinders to decrease the pitch to correct the underspeed which causes the valve 608 to move up and supply pressure to the underside of the servo piston 674 which moves up supplying pressure to the underside of the piston 90 and causing the sleeve 604 to follow up the valve 608. When overspeed condition exists the action of the governor valve 204 and servomotor 570 is reversed. The flow through the pipes 700, 494 is proportional to the speed error and the rate of change of speed error hence the piston 90 moves to correct the blade angle at a rate proportional to speed error and rate of change of speed error. When the " negative " pitch is selected by selector 58 the valve 438 is moved down to disconnect the pipe 700 and connect pipe 494 to a valve 436 which has been moved down from the position shown whereby the pipe 494 and underside of piston 90 is connected to exhaust and piston 90 moves down lifting the master-shaft 82 to operate the distribution valves 200, 201 to cause the blades to assume negative pitch. The action is reversed on movement of the selector 58 to the " feather " position, reduced pressure being supplied to the underside of the piston 90 to move it upwards. The valve 440 may be externally adjusted. A cam finger 702 connected by linkage to the feedback mechanism urges the valve 608 upwardly if a blade angle lower than a predetermined minimum is reached. Specifications 544,580, 545,520 and 637,323, [both in Group XXXIII], are referred to.