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Aviation History
1948
1948 - 2047.PDF
DECEMBER 2ND, FLIGHT 6G5 Discussing the Helicopter The Cierva W.ll "Air Horse"De- scribed and Evaluated : Ad- vantages and Dis- advantages of Three Rotors The Cierva W.ll "Air Horse" is powered by a Rolls-Royce Merlin engine. The all-up weight is 17,500 Ib. LAST week we dealt with four of the five papers readat the joint all-day meeting on November 20th of' the Royal Aeronautical Society and the Helicopter Association of Great Britain. In the following pages we give a summary of the paper read by Mr. Shapiro, of the Cierva Autogiro Company's technical staff. Mr. Shapiro recalled early schemes lor multi-rotor heli-copters, and said that by 1945 the Cierva company became convinced that neither the physical achievement of verticalflight nor the achievement of continuous operation could any longer be considered satisfactory aims. They were searchingfor a project which would offer economically sound commercial operation on a large scale. Such operation could only beenvisaged by increasing the size of the helicopter. The Air Horse design arose primarily as an answer to the demand forlarge loads. It was realized that difficulties increased in pro- portion to rotor diameter, and it was thus natural to increasethe number of rotors. Three rotors were chosen because a body in space is deter-mined by the position of three of its points, provided they are not in line. In the Air Horse the rotors have freelyflapping blades, and the three rotors turn in the same direction, torque reaction being counteracted by horizontal thrust com-ponents, obtained by built-in tilt of the rotors. The rotors are arranged with the single rotor in front and two side byside at the back. Control in pitch and roll is by lift couples obtained throughdifferential application of collective pitch to the three rotors. For control in yaw, cyclic pitch variation in the fore-and-aftphase is applied differentially to the side-by-side rotors. The machine is fitted with an undercarriage having a stroke offive feet and capable of absorbing the shock of high rates of descent. The airframe of the Air Horse is a semi-monocoque structurewith outriggers carrying the rotors and undercarriage. The canopy-covered cockpit is in front, equipped with fully dupli-cated controls and all necessary instruments. Behind the cockpit is a small luggage compartment through which thecrew enter the cockpit. The front undercarriage leg is attached to the fuselage frame at the rear of this compart-ment. Then comes the engine room, which contains, in addi- tion to the engine and its accessories, the distribution gearbox, the "control exchange" mechanism and its ancillary hydraulic equipment, and the fan and radiator unit. A fire-proof bulkhead separates this section from the main load compartment, at present fitted for freight-carrying only. Atail section completes the streamlining of the fuselage. It is in hinged halves to give unobstructed access to the compart-ment. There is a fixed tailplane with adjustable fins at its ends. Streamlined outrigger booms to carry the rotors and under-carriage are of semi-monocoque construction and streamline section to reduce drag at forward speed. The undercarriagelegs, supplied by Lockheeds, comprise telescopic tubes, the n T7 outer of which carry the loads while the inner constitute theoleo-pneumatic shock absorber. Palmer wheels and tyres are fitted. Power is supplied by a Rolls-Royce Merlin 24 with single-stage, two-speed supercharger. The cooling system layout is of shunt type and includes a light-alloy Marston radiator.The exhaust system is a specially developed '' cross-over'' manifold surrounded by a jacket through which cooling air isdrawn by the ejector action of the exhaust gas. The coolant radiator and the oil coolers (including transmission oilcoolers) receive a flow of air from a horizontally mounted variable-pitch fan drawing air from above and ejecting itdownwards through the radiators. The engine drives the distribution gears through itsstandard spur gear reduction and a clutch unit consisting of Genera/ arrangement of Cierva W.ll "Air Horse."
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