Patent GB-552557-A (GB)
Title: Improvements in the operation of aircraft retractable alighting gear
IPC: B64C25/22
Filed: 1941-07-08
Abstract: 552,557. Fluid-pressure servomotor-control systems. PHILLIPS & POWIS AIRCRAFT, Ltd., and MILLS, F. G. July 8, 1941, No. 8604. [Class 135] [Also in Group XXXIII] The retraction or extension of aircraft alighting gear, particularly the extension of the gear prior to alighting, is effected automatically by means sensitive to variations of airspeed or altitude independently of any action by the pilot. As shown, two jacks 19 for actuating an undercarriage, are supplied with pressure fluid from a pump 4 through a distributing valve 10 which is normally controlled by a manually-actuated lever 12 on a shaft 13 having an arm 14 connected by a link 15 to a lever 16 for moving the valve. The distributing valve 10 directs pressure fluid alternatively to the pipes 17, 18 leading respectively to the upper and lower ends of the jacks, return flow being through the other pipe and through a pipe 20 to a supply reservoir 3. The conduit 17 for extending the jacks includes a valve casing 25 connected by a pipe 24 to an electricelly-controlled valve 22 adapted to put the conduits 17 and 24 into communication with a comoressed air bottle 21 to effect rapid extension of the undercarriage when contacts 32, 33 are closed under the influence of a pressure sensitive device 35 operative upon a reduction of air speed prior to landing or upon the attainment of a predetermined atmospheric pressure. Consequently the under-carriage is extended automatically if it has not already been lowered by the pilot. The actuating device 28 of the valve 22 also actuates an explosive or other alarm to warn the pilot of his error and the valve 10 also is actuated to open the pipes 18 to exhaust by a lever 37 on the shaft 13 connected by a spring link 38 to the valve 22 or its actuating gear. Alternatively pressure relief valves may be provided on the jacks and in any case a pressure relief valve 27 is provided on the casing of the valve 10. Where automatic actuation without emergency actuation is required the air bottle 21 is omitted and the device 28 is connected directl yto the lecer 16. The valve casing 25 includes a ball valve 26 which normally closes the conduit 24 but upon emergency extension ot the undercarriage it is forced to the left to close the conduit 17 leading to the valve 10. The contacts 32, 33 are in series with switches controlled respectively by the landing flaps and the undercarriage position indicator so that the automatic device only functions when the flaps are down and the undercarriage still retracted. A manual cut-out switch is provided which may be opened also when the fuel cock is closed prior to a forced landing. The device may be used for automatically retracting an undercarriage by arranging the valve 25 in the conduit 18. An electro-motor may be used for actuating the undercarriage instead of the jacks 19 the motor circuit being actuated through a relay by the contacts 32, 33. Disturbance of trim due to actuation of the undercarriage may be corrected by connections from the undercarriage to the elevator or trimming tabs or biasing gear.