Patent GB-872265-A (GB)
Title: A combined jack and damper for aircraft landing gear
IPC: B64C1/22
Filed: 1958-08-08
Abstract: 872,265. Hydro-pneumatic shock absorbers. RECHERCHES ETUDES PRODUCTION. Aug. 8, 1958 [June 7, 1958], No. 25509/58. Class 108(3). [Also in Group XXXIII] A combined jack and damper for aircraft landing gear comprises an oleo-pneumatic damper capable of operating as an undercarriage retraction jack by being fully extended, and as a jack for changing the trim of the aircraft on the ground by being partially extended, the damper being under the control of two pressure oil distributers, one acting as a retraction distributer and the other as a trim change distributer. The combined jack and damper is so arranged that weight on the aircraft wheels puts the jack and damper under tension. In the Fig., the jack and damper cylinder 8 contains a piston 9 from which extend coaxial tubes 10, 11 separated by a free piston 13. Tube 11 contains a diaphragm, and the piston head 12a of a tube 12 secured to cylinder 8. Floating valves 19, 23 each ensure free flow of liquid in one direction, and throttled flow in the other direction. Cylinder 8 is thus divided into oil filled chambers 14, 15, and 20, and an air filled chamber 16. The interior of tube 12 is connected to an undercarriage retraction/extension distributer 5 having ports communicating with a high pressure line and a reservoir 4. Chamber 14 is connected through a non-return valve 24 to the annular space 39 between walls 28, 29, of a cylinder 3. Wall 29 contains an air space 34 defined by a piston 31 and chargeable with compressed air through a valve 35. The annular space 39 contains a free piston 30 defining a further space 33 connected to a trim change distributer 6 having ports connected to the high pressure line and the reservoir. The non-return valve 24 can be opened by a manual push rod 27 for testing or filling purposes, or by fluid pressure acting on a piston 26 controlled by a shuttle valve 7 connected to distributers 5 and 6. To retract the undercarriage, distributer 5 is placed in the position Th, with distributer 6 in the position N. This admits pressure fluid through distributer 5 and freely through valve 23 to chamber 20, expanding the jack. At the same time, the pressure fluid passes through valve 7 to act on piston 26 and open valve 24. The increasing air pressure in chamber 16 can thus drive piston 13 towards valve 19, fluid from chamber 15 passing freely through valve 19 into chamber 14, and thence through valve 24 to the annular space 39, compressing the air : in chamber 34. To lower the undercarriage, distributer 5 is placed in the position Tb, connecting tube 12 to the reservoir. The air in chamber 34 expands, forcing fluid through the now operative non-return valve 24 into chamber 14 to retract the jack. Fluid flows from chamber 20 to the reservoir during this retraction. After touch down, the jack acts as a damped shock absorber in the following manner. A force tending to extend the jack causes fluid to flow from chamber 14 through the throttling valve 19 to chamber 15, and moves piston 13 to compress the air in chamber 16, fluid being drawn from the reservoir into chamber 20 as required. The jack thus extends in a damped manner until the air pressure balances the external load, e.g. the aircraft weight, and acts as an oleo-pneumatic damped shock absorber. Relief or partial relief of the external tension load allows the compressed air in chamber 16 to expand, fluid passing freely from chamber 15 to chamber 14 through valve 19. The return of fluid from chamber 20 to the reservoir, however, is throttled by valve 23. Thus during landing, taxying and take-off, the compressed air inchamber 16 acts as the resilient member, and the fluid flow involved in shock absorbing movements of the jack is damped either by valve 19 or by valve 23. When on the ground, the aircraft can be raised or lowered e.g. for loading purposes, by action of the jack. To lower the aircraft, the distributer 6 is placed in the position Af. Pressure fluid then flows through valve 7 to act on piston 26 and open valve 24. The external tension load of the aircraft weight then extends the jack, lowering the aircraft, fluid flowing from chamber 15 to chamber 14 and thence through valve 24 into the annular space 39, compressing the air in chamber 34. The lowering is stopped at any point by returning distributer 6 to position N, closing valve 24. To raise the aircraft to its normal position for taxying and take off, distributer 6 is put into position Re. This admits pressure fluid to space 33, driving piston 30 to maintain the air in chamber 34 compressed and drive fluid from space 39 past valve 24 into chamber 14, retracting the jack. The raising is stopped by returning distributer 6 to position N. This connects space 33 to the reservoir enabling the air in space 34 to expand, and return piston 30 to its normal position. The jack is then ready to function again as a damped shock absorber.