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Aviation History
1953
1953 - 0017.PDF
FLIGHT, 2 January 1953 17 A NEW HYDRAULIC MOTOR UNTIL recently, auxiliary power requirements on British aircraft have been largely met by the use of electric motors and pneumatic and hydraulic jacks. But increasing demands have caused two new auxiliary power components to take their place in some aircraft systems : the high-capacity, high-pressure air compressor, and the hydraulic motor with a rotary drive. Bridsh Messier, Ltd., of Gloucester, are now able to release full details of a most interesting slide-valve hydraulic motor which is being built for certain new types of aircraft. The chief applica tion of this motor is likely to be in the actuation of large area- increasing flaps, the travel of which has, in the past, been too great to permit the use of a simple jack. The hydraulic motor is thus suitable for applications previously filled by heavy electric motors which frequently suffered from short-time ratings. The makers are to be congratulated on having achieved a power/weight ratio better than I h.p./lb, which can be maintained continuously; for brief periods appreciably higher powers can be obtained. Hydraulic motors also benefit from the precise control and virtually instantaneous stopping, or reversal, associated with nearly incompressible fluid systems. The motor has five piston assemblies which operate on a swashplate formed by the inner ring of a ball race. Admission to, and exit from, the cylinders is controlled by small slide-valves— one for each cylinder—which are reciprocated by a pair of cams. Other data are given in the accompanying table and performance graph. MAIN PORTS FROM PUMP TO TANK CASING DRAIN CAM PISTON SLIDE VALVE SWASH PLATE TO TANK This diagrammatic section shows one piston about to begin its power stroke; the spring prevents bounce on the return. CAM INLET AND CAM EXHAUST PORTS SWASH PLATE PISTON The British Messier motor is neat and compact. It is fange-mounted and can be installed in any position, preferably lower than the oil reservoir. Weight is 14.3 lb. oc 90 80 70 60 50 40 30 2D IO -v OVERALL EFFICIEN Oj> v>> CY.- 400 300 200 ui a a O 1000 2000 3000 PRESSURE (AT MOTOR PORT) (Ib/sq in) IOO 4000 Curves of input pressure against overall efficiency and output torque. The fluid is to D.T.D. 585 at 45/60 deg C, the speed 2,000 r.p.m., and the consumption 30 cu injsec. A production unit, after running-in and proof-testing, was exhaustively tested as follows : an endurance test was undertaken at 2,400 lb/sq in, 10,000 valve reversals being completed in 52J hours without fault. Calibration before and after the test showed very slight deterioration in torque in the clockwise direc tion, and a slight gain in overall performance in the reverse direction. Refrigeration to —60 deg C showed that an inlet pressure of 86 lb/sq in was required at this temperature to initiate movement. Static testing with the output shaft locked showed leakage from the two ports of 710 cc/min and 600 cc/min, respectively, at an inlet pressure of 4,000 lb/sq in, the allowable leakage being 1,000 cc/min. Specification Cylinder bore ... ... ... ... ... ... ... 0.53m Stroke (swashplate at 13J deg) ... Swept volume Maximum pressure Maximum-pressure torque Maximum r.p.m. ... Maximum-pressure output Minimum speed Minimum output (4,000 Ib/sq in) 0.672in 0.741 cu in 4,000 Ib/sq 400 lb in 2,500 15.8 h.p. 300 r.p.m. 1.9 h.p. "Exploded," the five piston and valve assemblies are revealed. The valves are actuated by disc cams mounted on the main output shaft. HELICOPTERS TO ASSIST TAKE-OFF? SPEAKING at the Convertiplane Congress in Philadelphia recently, Dr. J. Bennett said that a helicopter tug, beneath which a fixed-wing aircraft could be attached, could be used to assist the take-off and landing, thereby eliminating the necessity of large airfields. He explained that the tug would lift the fixed- wing machine into the air and release it at a forward speed within the speed range of both types. For landing, the fixed-wing craft would attach itself to the tug in the air "in much the same manner as aircraft are refuelled in flight by tankers." Dr. Bennett expressed the opinion that large aircraft carriers at sea would thus be rendered obsolete, and that it would become feasible for fixed-wing aircraft to operate from merchant ships on anti-submarine duties.
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