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Aviation History
1932
1932 - 0522.PDF
FLIGHT, JUNE 3, 1932 New Methods of Research S (IP^HIS year's Wilbur Wright Memorial Lecture was \^) II delivered before the Royal Aeronautical Society JIL by Mr. H. E. Wimperis, C.B.E., M.A., F.R.Ae.S., Director of Scientific Research at the Air Ministry, and Vice-President of the Royal Aeronautical Society, on May 26, in the Science Museum, South Kensington. Mr. Wimperis had called his lecture " New Methods of Research in Aeronautics," and recalled that it was twenty years ago, almost to a day, since the world was saddened by the news of the death of Wilbur Wright. In speaking of the early work of the Wright Brothers, Mr. Wimperis said that although their tools were primitive, their methods were scientific. " How different," he said, " from some of the impetuous inventors of to-day! '' Pointing out that nine years had passed since a Wilbur Wright lecturer dealt with the subject of research, the lecturer on that occasion being Dr. J. S. Ames, chairman of the American National Advisory Committee for Aero nautics, Mr. Wimperis said that in the world of aero nautics nine years was a long time, and that new methods of research had called for new tools. By these he meant the new wind tunnels of America and Europe, the new testing tanks for seaplane hulls, and the Farnborough vertical tunnel for spinning tests. What he proposed to do was to give a comparative study of these new tools in relation to the objects sought to be attained. Before dealing with the new tunnels, etc., Mr. Wimperis outlined the history and internal structure of British aero nautical research. The Compressed-air Tunnel The force which motion through the air applied to any structure might be very nearly proportional to the square of the speed, but not quite. A coefficient known as the Reynolds number was brought in. The law could be written: F = VaL.3f(R), where F was the force, V the velocity, L the principal length and R the Reynolds number. If this were con stant, it would be easy to transfer results from model to full scale. Unfortunately, it varied with the velocity, the length, and the kinematic viscosity of the fluid in which the motion took place. The new wind tunnels aimed at the reproduction of the actual Reynolds number. In the new British compressed-air wind tunnel it was possible, by increasing the density, to test models at full Reynolds number without the need to go to large models or high speeds. Mr. Wimperis gave the following comparative data of the American and the N.P.L. compressed-air tunnels: American British tunnel. tunnel. Diameter of jet (ft.) Pressure (in atmospheres) Wind speed (ft./sec.) .. Reynolds number Mr. Wimperis pointed out that the fact that we were aiming at a Reynolds number nearly twice the American was a result of the greater speeds attained by aircraft since the American tunnel was built, and the fact that we had been able to profit by America's experience, which had been fully communicated by the American N.A.C.A. The Large Air Tunnel at Farnborough Before dealing with the reasons which led to the con struction of the new 24-ft. jet tunnel at Farnborough, Mr. Wimperis recalled the experience of the American N.A.C.A., first with their 20-ft. tunnel and recently with their new 5 20 70 R 6 25 90 .. 1.93R FOR WORK AT FULL REYNOLDS NUMBER : The compressed-air, or variable density tunnel at the National Physical Laboratory at Teddington. The tunnel was made for the N.P.L. by John Brown & Co., Ltd., of Sheffield, while the steel rings and domed ends were made by Firth & Sons, Ltd. The inside diameter of the tunnel is 17 ft. and the finished weight 230 tons. 482
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