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Aviation History
1957
1957 - 0745.PDF
31 May 1957 The M.L. Utility Mk 1, with its inflatable wing, "buzzes" cameramen to give them a close-up view. At right, David Masters, the Fairey test pilot who flies the Utility, in the front seat. AIROPLANE The Inflatable-wing M.L. Utility Mk 1 Demonstrated LAST week, at White Waltham, the M.L. Aviation Company,Ltd., gave a remarkable and very convincing demonstrationJ of their Utility Mk 1. In two years of development under M.o.S. contract, the principle of the inflatable wing, originallyconceived by the M.o.S. research and development establishment at Cardington, appears to have been well proven. For the purposes of the demonstration, the wing was blown upin about 15 minutes by a small electrically driven pump, fuel tanks were attached under the wing, the engine was started and themachine took off in a very short space. In bumpy conditions David Masters, the test pilot loaned by Faireys, drove it roundvery purposefully, clearly displaying its controllability in turns very close to the ground and during several take-offs and landings.After the flight he said that the machine was very light, but remarkably stable directionally and laterally. He doubted whethera Tiger Moth pilot, for example, would find the Utility altogether easy to fly, as it has a delta wing and is controlled by elevons.But there was no great problem in handling and, though a stalling speed of 30 m.p.h. was officially quoted, it was doubtful whetherthe elevons were in fact powerful enough to achieve the stalling angle of attack. Mr. Masters added that behaviour close to thestall was quite straightforward. About 40 hours' flying have been completed to date. The Utility Mk 1, registered XK 776 (the second machine built),consists of a two-seat gondola-type open fuselage mounted by faired but unsprung legs on three large-tyred wheels. The nose-wheel is directly controlled by pedals for steering on the ground. There is no direct aerodynamic control in the yawing plane and,though the pilot normally uses the rudder bar instinctively, he obtains no directional control in the air from swivelling the nose-wheel. On the ground, the nosewheel does give very precise directional control and a very tight turning circle. Cable-operatedbrakes, controlled from a single lever on the cockpit coaming, are mainly for parking, but they were also effectively used to shortenthe landing run. Mounted on the rear of the gondola, the little inverted four-cylinder Walter Mikron drives a two-bladed wooden propeller. Instrumentation consists of an altimeter with its own static sensing-head attached; a tinplate-and-spring A.S.I, of the Tiger Moth pattern; E.2A magnetic compass; wing-pressure gauge and warn-ing light; and r.p.m. and oil pressure gauges. For test purposes a battery-operated, single-channel V.H.F. set is carried and thepilot wears a parachute. The rear cockpit is decked over and the enclosed space taken up by test instrumentation. Made up of light wooden spars, with a loose khaki-fabric cover-ing, the gondola carries a longitudinal beam overhead which acts as the locating and support structure for the inflatable wing. Afelt gasket prevents scuffing and main wing-to-gondola attachments are in the form of Terylene rope harnesses. This type of rope isalso used for the series of lift wires. Four on each side are moored to a fitting on the relevant mainwheel axle and three others areattached at the nosewheel mounting bulkhead. Their length is preset and no rigging adjustments are required during preparationfor flight. The rigidity of the wing is maintained entirely by air pressureat 0.5 lb/sq in, supplied initially by electric or hand-operated pump and, in the air, by an electric pump inside the gondola. This canbe left to run continuously or switched on as required. To com- pensate for increases in pressure caused by continual pumping, orby temperature and altitude changes, a relief valve is built into the underside of each wing, close to the leading edge alongsidethe gondola. The profile of the symetrical aerofoil (series 0024 modified) is maintained by a number of spanwise porous-cottondiaphragms designed to permit the passage of air during inflation or retard it after damage. A puncture caused by bird strike, riflefire from the ground, or other incident, would therefore not become catastrophic before the pilot had a chance to make an emergencylanding. The fabric of the wing envelope itself is of rubberized cottonof a drab colour. Elevon hinges are in the form of fabric tubes, which give some stiffness as well as transferring air to these other-wise separate surfaces. A short kingpost and guy ropes maintain the rigidity and required deflection angles of the elevons, the lowerend of the post being linked by wooden push-pull rod to the outermost bell-crank of the control run. A length of bungeestretched from elevon trailing-edge to a point on top of the wing provides a form of mass balancing. Another bungee provides atrim force on the stick. The aircraft is generally insensitive to load changes, as both fuel and passenger loads Ere virtually on thee.g. Larger alterations can be accommodated by shifting the wing on its mounting—on the ground, of course. The very low e.g.materially assists stability. Fuel load is carried in two cylindrical tanks, each holding sixImperial gallons, slung on tape cradles under the wing and con- nected to the carburetter by flexible piping. They are filled beforebeing set in place. A fuel-quantity reading is given by a vertical polythene pipe attached to the side of each tank. Directional stability in the air is assisted by small rectangular The inflation sequence from the rigged (but collapsed) state to nearly complete erection. The fabric inflation- pipe is attached at one wing-tip. An electrically driven centrifugal air pump does the job in about IS minutes. "Flight" photographs
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