Patent GB-405660-A (GB)
Title: Improvements relating to shock absorber struts for aircraft
IPC: B64C25/60
Filed: 1932-08-09
Abstract: 405,660. Shock-absorbers. DOWTY, G. H., 17, Lansdown Crescent, Cheltenham. Aug. 9, 1932, Nos. 22257 and 22258. [Class 108 (iii).] An aircraft undercarriage strut comprising combined resilient and fluid-friction shock-absorbers is provided with coaxially arranged resilient elements operating substantially in parallel and with a valve or valves operated by the flow of fluid to vary the resistance to the passage of fluid. As shown in Fig. 1 tubes 1, 5 and 7 telescope under compression, the tube 1 carrying a hollow piston rod 4 with piston 17 which forms an enclosed liquid chamber 24 with an annular liquid-sealed guide 10 fixed in the tube 5, the end of the tube 5 being closed by a liquid-sealed piston 6 provided with a valve 26 floating on a bored guide 26a. The stroke of the piston 6 is limited by a sleeve 7a in the tube 7 and that of the piston 17 by the abutment of a spring 22 against the guide 10. The piston 17 is bored to receive a hollow valve stem 14 with a disc head 15 maintained in a floating condition in the piston by opposed springs and adapted under compression to close ports in the piston 17, except for the leak holes through the disc, and under extension to abut an opposing valve seat 18 in the piston. A spring 30 surrounds the piston rod 4 and a spring 25 is mounted in the tube 5, the tube 5 being filled with liquid on both sides of the piston 17 and also the tube 7. Under compression the valves 26 and 15 close so that liquid only passes the pistons through the leak holes and the springs 30, 25 are compressed in parallel whilst the liquid resistance is in series with the parallel arrangement. Under extension the valve 15 abuts the seat 18 and the flow of liquid from the chamber 24 is restricted and prevents rebound of the springs, the amount of damping provided by the valve 15 may be arranged to be greater or less than the damping on the compression stroke by arranging the leak holes in different positions. In Fig. 3 (not shown) two telescopic tubes are shown, one having two annular stops forming spring abutments and three springs, the first spring lying between the first abutment and the end of the other tube, the second between a flange on the piston rod and the second abutment and the third between the piston and the end of the tube. All three springs are compressed in parallel, the liquid in the chamber surrounding the last spring being passed through the piston in a manner similar to that in Fig. 1. In Fig. 5 (not shown) a floating piston and rod are enclosed in two telescopic tubes filled with liquid, a spring bearing on the end of the piston rod and another under the piston. Fig. 6 shows one half of a retractable undercarriage leg each comprising complete shock absorber units hinged at 63 and locked at 64. The tubes 1 and 65 telescope and piston rod 4 is surrounded by springs 68, 68A which may have different deflection characteristics. Similar springs 69, 69A are housed in the liquid chamber 71. A ball valve 60 allows the passage of liquid from the interior of the piston rod to the chamber 70. In compression the springs 68, 68A and 69, 69A are compressed in parallel and the liquid in the chamber 71 passes through the valve controlled openings in the piston to the chamber 70. Instead of a flat disc valve 15 with perforations connected by an annular channel as shown in Fig. 1, the valve may be as shown in Fig. 4, the piston 32 with holes 17 being provided with an annular ring 39B forming valve seats for valves 39, 40 which are perforated with leak holes, the valve 39 being held off its seat by a spring 39A. The valve 40 is forced onto its seat by the liquid in the chamber 35 during compression of the leg and sets up a fluid resistance whilst the valve 39 is forced on to its seat by the liquid in the chamber 4 on the rebound action of the leg and regulates the extension of the leg. Specification 322,657, [Class 108 (iii)], is referred to.