585,231. Shock-absorbers. FOCHT, N. S. Sept. 19, 1944, No. 17863. Convention date, Nov. 6, 1943. [Class 108 (iii)] A shock-absorber comprises a compressed-air chamber B, Fig. 1, a liquid-containing chamber A, and a liquid-metering valve device consisting of a piston 22, Fig. 2, slidable in a casing 18 and exposed at one end to the air pressure in chamber B which urges the piston in one direction against the action of yieldable means. Registering ports in the casing and piston are shaped to provide a different effective combined area for each position of the piston in the casing, liquid being forced on compression of the shockabsorber from the chamber A through the ports to raise the pressure of the air in chamber B. As shown, the shock-absorber constitutes a landing-wheel strut for an aircraft fuselage 12, the wheel 13 being carried by a piston 11 slidable in the cylinder A. The valve casing 18, which is secured in a partition 16 and is always covered by liquid, has a pin-and-slot connection with the piston 22 to prevent relative rotation thereof. Pairs of diametrically-opposed arcuate ports 19, 20 are provided in the casing immediately below and above the partition and co-operate with ports 35, 36 in the piston, shaped as shown in Fig. 2. A plunger 29 extending from the bottom of the piston 22 is slidable in a small air-containing cylinder 26 either integral with the end wall 21 of the casing or held against the wall by a spring 28 acting between a flange 27 on the cylinder and the piston, and a rod 30 extending upwardly from the piston carries a slidable disc valve 31 normally pressed by a spring 33 to close the open end of the piston. The cylinder 26 may be vented to the atmosphere. One of more holes 34 in the bottom of the piston provide constant communication between the spaces on each side of the piston. Operation.- The air pressure in the chamber B is communicated through the disc valve 31 to the piston and as the lower end of the piston is of less effective area than the upper end owing to the plunger 29, the air pressure in chamber B tends to move the piston downwardly against the action of the spring 28, so long as the air pressure is approximately equal to the liquid pressure in chamber A. When 'the shockabsorber is fully extended and unloaded, the disc valve 31 is closed and the lower portions of the ports 35, 36 register with the ports 19, 20. On compression the shock-absorber, as the piston 11 moves into the cylinder A, liquid is forced through the ports 19, 35 into the piston 22 and thence through the ports 20, 36 and also past the disc valve 31 into chamber B. Thus, the air pressure in chamber B is increased and moves the piston 22 downwardly until it reaches the lowermost position when the shock-absorber is fully collapsed and the air in chamber B is under maximum pressure. The ports 35 are so shaped that initial downward movement of the piston 22 causes a rapid reduction in the effective area of the ports corresponding with a gradual deformation of the landing wheel tyre 14. As the tyre approaches normal deformation, the portions of the ports 35 in register with the ports 19 increase in area, thus decreasing the resistance to flow of liquid, increasing resistance to compression of the shock-absorber being cffered, however, by the increasing compression of the air in chamber B. In the event of heavy shocks, e.g., during landing of the aircraft, progressively decreasing areas of the ports 35, above their widest portions, provide for progressively increasing high resistance. On recoil, the disc valve 31 closes and liquid is forced to pass through the ports 20, 36, the effective area of which decreases progressively. Modifications. In another construction in which the shock-absorber is disposed in an inverted position relatively to that shown in Fig. 1, the valve casing 18 is mounted in a piston at the end of a hollow plunger which is connected to the landing wheel and contains a floating piston movable to compress air beneath it in the plunger. In a further construction in which the shock-absorber is used in a lever suspension for an aircraft landing gear employing an endless track, the piston port 35 is of triangular shape, the irregular shape shown in Fig. 2 being unnecessary in the absence of a pneumatic tyre. Fig. 10 shows a different construction of valve mechanism in which the'end wall 23a of the piston 22a is extended to form a wall 44 to accommodate the spring 28a and to afford a liquid-containing 'space between the end walls 23a, 21a of the piston and valve casing 18a.