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Aviation History
1949
1949 - 0584.PDF
AIR HORSE Design Analysis' of the Largest and Heaviest Helicopter in the World WHEN the Cierva W n Air Horse was firstexhibited to public view at the S.B.A.C. Farn-borough Display last September, it created an enormous amount of interest. To the layman it presented an uncouth picture of almost Wellsian fantasy, but to the technician it appeared as the fruition of years of pains- taking development and a very considerable stride forward in the art of rotary wing aircraft. Over the years, Flight has published many articles cover- ing the process of development which forms the pedigree of the Air Horse, but we feel it relevant to restate a synopsis of the main line of development, if only to give perspec- tive to the review of the aircraft itself. Helicopter development in this country really sprang from the W.3 jump-start Autogiro, built in 1933 by G. and J. Weir, Ltd., as licensees of the Cierva Company. The problems involved in this aircraft made transition from the autogiro to the helicopter a logical step, and as a result, Mr. C. G. Puffin, who was chief engineer of the Weir rotating wing department, started to work on such a project. An enormous amount of pioneer research was entailed and it necessarily took a good deal of time. At last, however, the results of these years of labour were embodied in the twin side-by-side rotor W.5. This air- craft, which made its initial test flight in June, 1938, was the first British helicopter to achieve free controllable flight. (Incidentally, it is worth noting that Igor Sikorsky did not make his first successful helicopter flight until 1940.) The following year, 1939. the W.6 made its appearance and flew successfully : a somewhat larger, metal, 200 h.p- engined version of the little W.5, it employed the same basic configuration. Work on helicopters then unfortun- ately had to give way to the urgent demands of war, and it was not until ,1944 that progress could be resumed. Although conceived chiefly as a solution to the omni- present problem of torque reaction, the Pullin side-by-side rotor layout had proved to be possessed of excellent flying and control characteristics, although fore and aft stability in the pitching plane was known to be a subject for im provement. Thus, when thoughts on helicopters were once more engaging attention, a third, balancing, rotor was envisaged to give " tail surface " compensating effect. A full-sized mock-up was made in the form of a skeleton employing hardly any fuselage worthy of the name, and it was this design study which was first christened the Air Horse (Flight, July 4th, 1946). Tunnel tests were made at the Royal Aircraft Establishment during 1946 with the three-rotor configuration, as a result of which the theory was proven that the third rotor should be positioned at the front of the aircraft rather than at the back. .';. Within the present ambit of knowledge and practic- ability , an effective limit is set on rotor diameter to some- thing of the order of 50ft., and as the functions of lift and control are dependent on rotor parameters, the amount that can be lifted is, to a certain extent, dependent on the number of rotors employed. Thus, each rotor of the W.i 1 has something of the same ratio of lifting capacity as the Bristol 171 and the Sikorsky S.51, the three rotors enabling the aircraft to fly at an all-up weight of 18,000 1b.
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