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Aviation History
1939
1939 - 0371.PDF
FEBRUARY 9, 1939 FLIGHT. 143 DELAYING the STALL Flight Tests of Compound Aerofoil About to Begin : Willoughby Delta 8 as Flying Scale Model of Large Passenger Machine, Delta 9 RATHER more than a year ago, on November 18, 1937, to be exact, Flight published a brief advance • description of an interesting project which is now about to become a reality. In that issue of Flight we gave the general arrangement drawings of a small two- seater designed and to be built by the Willoughby Delta Company, of 20, Kingsway, London, W.C.2. That the construction of this machine has taken so long is due in part to the fact that it was desired to obtain results of extensive pressure plotting tests with a wind tunnel model before completing the actual machine. In the meantime these tests have been made and the two-seater, which has been named St. Francis, is now all but ready for its flight tests at Witney aerodrome, Oxford, where it has been constructed. It should be explained at the outset that the two chief aims in the design were to provide an airform which should be, for all practical purposes, free from the vice of stalling, and which should, at the same time, be an approach to the all-wing ideal and should carry its load well distributed spanwise so as to make for low structure +*• weight. The all-wing idea was, of course, first suggested in the now-famous Patent of the late Professor Junkers, taken out in 1909 or 1910. Even if a longitudinally stable wing is produced, by using a reflexed curvature, it is necessary, in the ordinary high-aspect ratio wing, to go to a very large size before sufficient headroom can be provided within the wing. With the airform developed by the Willoughby Delta Company there is an opportunity of approaching the all- wing ideal without introducing an excessive size. Much research work was necessary before even the small machine, which is intended as a flying scale model of the large type contemplated, could be designed and built with any assurance that it had no unsuspected tricks. The plan form is so unusual that stability and control data derived from orthodox aeroplanes were of little use as a guide. Mr. Willoughby has had very extensive wind tunnel tests made both in this country and in America. Tests in England include such research establishments as the N.P.L., the City and Guilds, Farnborough, and Queen Mary College. And in America pressure plotting tests were made at the Guggenheim Institute of the New York Lift distribution, from pressure plottings, on side wings, centre-section and wing tips at large and small angles of incidence. At high speed the side wings carry practically no load, but at low speed they take over a fairly large proportion of the total lift.
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