Patent GB-473387-A (GB)
Title: Improvements in or relating to retractable alighting gear for aeroplanes
IPC: B64C25/22
Filed: 1936-11-16
Abstract: 473,387. Pneumatic springs. EHRHARDT, P. G. Nov. 16, 1936, Nos. 31257 and 31258. Convention dates, Nov. 14, 1935 and Nov. 10, 1936. [Class 108 (iii)] [Also in Groups XXXIII and XVIII] Relates to retractable undercarriages of the kind in which the shock-absorber and the device for retracting the wheels have been combined to form the same cylinder with piston and liquid adapted for both purposes and comprises a piston connected to the landing gear and movable in a cylinder filled with liquid maintained under pressure by a gaseous medium contained in a chamber connected to the cylinder and separated from the liquid by a yielding and flexible partition, In one form, Fig. 2, a wheel 4 is carried by a leg 5 pivoted to the aircraft at 6 and connected by hinged struts 7, 8 with a fixed pivot 9. Movement of the struts is controlled by a piston rod 10 and piston 11 moving in a cylinder 12, Fig. 3, also pivoted at point 6. Cylinder 12 is filled with liquid and connected at one end to a storage tank 23 by a pipe 13 and valve 16 and at the other by a valve 25 with an airchamber 14 also communicating by a pipe 15 and valve 17 with tank 29. Chamber 14 contains an air bag 26 inflated through pipe 27 and valve 28. Air bag 26 is shaped to fill chamber 14 when the gas pressure exceeds the hydraulic pressure. Valve 25 is arranged so as to impede flow from chamber 14 to the cylinder without substantially impeding flow in the reverse direction. Valves 16, 17 are respectively connected by pipes 18, 19 with a reversible pump 20, and are interconnected in such manner that both may be closed or both opened to establish communication between pipes 13, 15 and tank 29, or so set that either pipe 13 or 15 communicates with the pump only and the other with the pump and the tank. For retraction liquid is pumped through pipe 18, valve 16 and pipe 13 to cylinder 12 and the liquid displaced by piston 11 passes through valve 25, chamber 14, pipe 15 and valve 17, to the suction side of pump 20. On the completion of retraction valves 16, 17 are closed and a securing member 36, Fig. 2, placed in position. For extension, valves 16, 17 are both opened to the storage tank allowing the leg to sink under the action of gravity or are oppositely set and pump 20 driven to force fluid through chamber 14 and valve 25 to cylinder 12. In either case the pressure within the system can be raised by the pump to the desired value for alighting. A pressure gauge 30, indicates the pressure of the liquid and a gauge 31 indicates the pneumatic pressure when the air bag 26 expands sufficiently to touch the walls of the chamber 14. Fig. 4 shows a modification in which a pneumatic chamber 14<1> is separate from a cylinder 12<1> to which it is connected by a flexible pipe 33. Chamber 14<1> and air bag 261 are approximately globular. Valve 25 is arranged in pipe 15, substituted by a valve 34 at the inlet of chamber 14<1>, or two valves are arranged as shown. In this form the piston rod 7 may be on the side of the piston which is not subject to the pressure of the air chamber as shown in Fig. 8.