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Aviation History
1936
1936 - 1221.PDF
504 FLIGHT. MAY 14, 1936. MODERN AERODYNAMICAL DEVELOPMENT A "Popular" yet Accurate Reviezv by the Superintendent of the Aerodynamics Department of the N.P.L. •^mi&saBiMekSSfc.-' TWENTY-TWO YEARS AGO : One is reminded of the old saying that "there is nothing new under the sun" by this photograph of the S.E.4, which was designed and built by the Royal Aircraft Factory (now the Royal Aircraft Establishment) in 1914. The machine was flown in June of that year by Mr. (now Group Captain) N. C. Spratt and by Major (now Marshal of the Royal Air Force Sir John) Salmcnd. It is interesting to note that the machine incorporated such "modern " features as a streamline fuselage, faired axle and strut joints, inter-plane I-struts, four-bladed airscrew with spinner, long-chord engine cowling, and variable-camber wings. Later the pilot's cockpit was roofed in. THE forty-second James Forrest Lecture before the Institution of Civil Engineers was given last week by Mr. Ernest F. Relf, A.R.C.Sc, F.R.Ae.S., Superin- . terident of the Aerodynamics Department of the National Physical Laboratory. Mr. Relf gave a masterly review of what has been achieved during the last six years (Professor R. V. Southwell delivered his lecture—the pre vious aeronautical lecture in this series—in 1930) and succeeded in treating his subject, "Modern Developments in the Design of Aeroplanes," in a manner which, while perfectly clear to an audience consisting of civil and not of aeronautical engineers, would have passed muster by the most critical high-brow scientist. In other words, Mr. Relf was "popular" without being inaccurate, instructive with out being condescending. Flight would have liked to publish the paper in full, but space does not permit. Mr. Relf called attention to the fact that in 1914 Dr. Lan- chester prophesied that advance in aircraft performance would come mainly from aerodynamic sources, and that no great improvement could be expected from increased efficiency of the petrol engine. Professor Southwell, in 1930, showed clearly that this was one of the rare occasions on which Dr. Lan- chester's predictions had not been correct. During the last six years, Mr. Relf continued, the pendulum had swung over to Dr. Lanchester's side, and great advances had been made in aerodynamic efficiency. By way of an example the lecturer made a comparison between the Fairey Fox, a good machine of 1930, and the De Havilland Comet. The Fox had a top speed of 152 m.p.h. with an engine of 540 b.h.p., and the Comet did 235 m.p.h. with two engines totalling 470 b.h.p. Of the Comet Mr. Relf said that, "There were no elaborate wind tunnel tests 011 this machine; it was produced simply by the determination of a very able designer to apply all the available ideas en aerodynamic and structural improvement. It was built in an amazingly short space of time, and its suc cess was phenomenal." While on the subject of surface smoothness, Mr. Relf men tioned that the Fairey company had made a model by press ing indentations into a thin copper sheet and wrapping it around a wooden aerofoil, the object being to simulate the rivet heads used in stressed-skin construction. At low Reynolds numbers the drag curve broke away frora that for the smooth wing, but as the Reynolds number increased, a maximum was reached, and then there was a falling until, at the upper limit, the curve was not much above that for a smooth wing. The Use of Slots Of the Handley Page leading-edge slot Mr. Relf said that it was not very useful in reducing landing speed, as it needed a tall undercarriage to get the necessary large ground angle. The slotted flap developed by the same firm he described as better than the split flap because it gave greater extra hit with very little change of drag when put at a small angle, and was still as effective as the split flap for landing when put down to 60 degrees or so. - - , Discussing stability, Mr Relf mentioned that cases nau occurred recently in which the stability of some of the moder monoplanes had not been satisfactory, because t'lc.,lU't developed from experience of the thin-wing biplane could n be applied sufficiently well, and also because there exis e relatively little experimental data on the stability denvatw of the monoplane in comparison with data for the o types of machine. Research was in hand, and there was ' ^ likelihood of dangerous instability in the new designs, D great deal of time would be lost if the new machines haa
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