In hydraulically‐operated retractable wheels for aircraft the actuating member comprises a jack having a piston connected on one side with a motive pump and an exhaust, and on the other side with a hydro‐pneumatic pressure accumulator into which the liquid is forced by the jack during each lifting operation, the stored energy in the accumulator actuating the jack to assist the action of gravity when lowering the wheels. The retractable wheels R (Fig. 1) are each pivoted at A and connected to a fluid‐operated piston in a cylinder V pivoted at T, the wheels being drawn up into the machine through spring‐operated doors C1, D1 which are opened by fluid‐operated means G2 (Fig. 2) when the wheels are lowered. The cylinder V is connected by pipe 3 and non‐return valve 4 to a pump 1 supplied from a reservoir 2, surplus liquid being bye‐passed from the pump through a pipe 16. A pipe 5 for exhausting the cylinder V is connected through a manually‐operated valve 6 to the reservoir 5 and a branch 3a from the pipe 3 is connected to a cylinder 8 whereby pressure is applied to move valve 12 and non‐return valve 10 to place the other end of the cylinder V to discharge through pipes 3b, 3e to a pneumatic accumulator 9 supplied with air from a cylinder 14. When pressure is supplied by the pump 1 to the cylinder V to retract the wheels, a projection on the valve 12 opens the valve 10 and the liquid in the other end of the cylinder is forced into the accumulator 9, and when the wheels are to be lowered the valve 6 is opened by the lever 7 to exhaust one end of the cylinder into the reservoir 2 while the other end of the cylinder is supplied with pressure fluid from the accumulator. A pipe 17 from the pump 1 is connected to a cylinder G2 and is provided with a branch 18 and manually‐operated valve 19 whereby the cylinder may be exhausted. The cylinders G2 (Fig. 5) are connected by links to the doors C1, C2 maintained in the closed position by springs r1, r2, the doors C1, C2 being interconnected to open smaller doors D1 (Fig. 1) which remain open when the wheels R are lowered. The levers 25, 20, 7 (Fig. 2) are connected to a single control lever. In Fig. 10, the wheel arm J is pivoted at A and is connected by piston rod P to the cylinder V pivoted at T. A wire 35 connected to the arm J passes over pulleys 36, 37, and is connected to a piston in a horizontal cylinder 41 open to a pneumatic reservoir 9. When the wheel R is raised to the position R1 by the admission of fluid under the piston P, the wire 35 rapidly withdraws the piston in the cylinder 41 to compress the air in the accumulator 9, and since the effect of gravity is not so pronounced between the positions R, R1 as between R1, R2 and the fact that the air pressure on R tends to raise the wheel, the pressure applied to the piston P is mainly stored in the accumulator 9. From the position R to R1 the effect of air pressure is less and gravity greater, so that between these positions the wire 35 is adapted to lap around a pulley 43 on the axis A whereby the movement of the piston in the cylinder 41 is small and less power is stored in the accumulator 9, the pressure on the piston P being primarily expended in raising the wheel from R1 to R2. Similarly when lowering the wheel the accumulator expends the greatest power between R1, R. A device for recovering any leakage from the pump 1 when the reservoir 2 is at a higher level is shown in Fig. 9. A leakage pipe 28 is connected by a housing 29 and pipe 30 to the suction pipe 33, and the housing contains a float 31 with upper and lower needle valves. When the housing 29 is full of liquid, the pipe 28 is closed by the upper needle valve and the liquid in the housing is withdrawn through pipe 30 and when the housing is empty the float falls and closes the pipe 30.
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