GB702079A - Improvements in or relating to aircraft undercarriages - Google Patents

Abstract

. 702,079. Hydraulic shock absorbers. BRITISH MESSIER, Ltd. May 15. 1952 ,[July 6, 1951], No. 16129/51. Class 108(3) In an aircraft undercarriage means operable at will are provided to prevent or reduce the yielding of a shock absorber during take-off, the means being arranged for further and automatic operation after take-off to restore the shock absorber to the normal yielding condition before landing. The invention is described as applied to a shock absorber similar to that disclosed in Specification 451,901. A hollow plunger 12 has a head 18 slidable within a cylinder 11 and over a hollow piston rod 16 which is rigid within the cylinder 11. The rod 16. carries a piston 17 slidable within the hollow plunger 12. The interior of the piston rod 16 is connected with the main cylinder space 27 by radial ports 20 which terminate in restricted orifices 21 and ports 22 controlled by a oneway valve 23. A space 26 between the piston 17 and the head 18 is connected with the space 27 by restricted orifices 24 controlled by a one-way valve 25 and with compressed air space 15 in the plunger 12 by one-way valve-controlled ports 29. A piston 31 is operable by rotation of a cam 37 (acting on plunger 33 and spring 35) to close the ports 20. The cam 37 is actuated by a lever 38 against a return spring 39. Operation.-When the piston 31 is in the position shown in Fig. 1, the shock absorber functions as an hydro-pneumatic device. On compression, the valves 23, 25 close, and liquid flows through the orifices 21 into the space 15 via the piston rod 16. Liquid also flows freely from the piston rod 16 through the open valve 29 into the space 26. On extension, liquid flows back freely from the space 15 via the open valve 23, and liquid in the space 26 is forced through the orifices 24. When it is desired to render the shock absorber rigid to compression loads the lever 38 is rotated anti-clockwise until a notch 40 in the cam 37 engages the end of the plunger 33 (Fig. 2). The piston 31 then covers the ports 20 and prevents all flow from the space 27. This engagement may prevent return of the lever by the spring 39. A duct 42 transmits pressure in the space 27 to the underside of the piston 31 and releases the lever 38 which returns. to its Fig. 1 position. When all compressive load is relieved, as when the aircraft becomes airborne, pressure in the space 27 drops and the piston 31 is returned to the Fig. 1 position by the spring 35. The invention is applicable to the nose wheel of an aircraft designed for assisted take-off.