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Aviation History
1925
1925 - 0279.PDF
MAY 7, 1925 Symbol A im. q = kg/m^ Reynolds No. I 00 e.sa £37 10.20 26.1 173.00067 6 440,000 151 0 940,000305.0 1,820,000 19.80 62C.0 3.470,000 Gottingen 387 Liff and drag choracierisiics as tesied in the —"'—Variable Density Wind Tunnel from I to I9.Q atmospheres. number of different airfoils, etc., indicates that this apparatus, or the equivalent, is essential if we are to make a thoroughly reliable second approximation to the performance of an airplane from model tests. " Reynolds' number—LV jv—is a compound ratio whose numerical value in the case of any given object depends upon the ratios between the actual values of LV and v and their unit values. Unfortunately, each type of object has its own series of Reynolds' numbers, because as a rule the values of L are not comparable for dissimilar objects. Thus, for an airplane wing we naturally use for L in Reynolds' number the length of the chord. For an airship we would use the length or the diameter or any linear function of the two. But L for the airship wouldjnot be comparable with /. for the airplane. "" " Considering airplanes as they are using the chord of the wing in inches as L, and speeds in statute miles per hour, the Reynolds' numbers come out fairly large. Thus, for an airplane of 5-ft. chord, at 100 miles per hour in a normal atmosphere the Reynolds' number will be some 4,800,000. For its model of 6-in. chord in a wind tunnel at ]00 miles per hour with normal air the Reynolds' number will be 430,000. " Attention is invited now to Figs. 1 to 3, giving in con- densed form results of recent tests of three airfoils of well- known form in the variable density wind tunnel. Necessary' data as to the conditions and the airfoil section to which they apply are shown on each figure. Results are plotted as curves of lift and drag coefficients as ordinates over angles of attack—a as abscissa;, following the standard practice of the U.S. Advisory Committee. Fig. 1 shows results for an American section, U.S.A. 27 ; Fig. 2 shows results for a British section, R.A.F. 15 ; Fig. 3 shows results for a German section, Gottingen 387. It happens that these three typify the medium, the thin and the thick sections. " Ignoring minor eccentricities due to accidental causes, unavoidable experimental error, etc., these curves seem to warrant a few broad conclusions which, by the way, are in agreement with other results too numerous to include. In the first place, the scale effect appears to have more influence upon the drag than upon the lift. This may be explained upon theoretical grounds. " In the second place, the scale effect increases more and more slowly as the Reynolds' number increases, so that conclusions drawn from experiments with airfoils within the Reynolds' number range of ordinary wind tunnels cannot safely be extended to much larger Reynolds' numbers. " In the third place, the consistency of the results gives us reason to think that for present-day airplanes we are justified in ignoring the effect of other factors than Reynolds' number in reaching our second approximation to aero- dynamic properties of airfoils. " In the fourth place, the thin airfoil appears to show less scale effect than the thick airfoil. " In the fifth place, so far as airfoil action is concerned, the scale effect is, after all, secondary, though by no means negligible when we undertake to estimate closely. '' The comments above apply only to airfoils. They do not necessarily apply to wires, struts, etc. Such appendages can be tested separately in the ordinary wind tunnel at Reynolds' numbers much closer to the numbers on the full- sized airplane than is possible M*ith the airplane structure proper." The last sections of Dr. Taylor's paper dealt with the subject of airscrews. Wright Bros.' Historic Biplane for England ORVILLE WRIGHT has announced that it is his intention to present the original Wright biplane, designed and con- structed by himself and his brother, to the Science Museum, South Kensington. This machine, which made its first nights at Kitty Hawk, South Carolina, on December 17, 1903, will, indeed, form a most valuable and acceptable addition to the already extremely interesting collection of aircraft exhibits at South Kensington. Royal Air Force Iraq Dinner IT is proposed to hold this dinner at the Holborn Restaurant, at 8.15, for 8.45, on the evening of June 27, 1925 (the day of the R.A.F. Display). All tickets must be applied for before June 1, 1925, and a remittance must accompany the application, together with a statement of the unit with which the officer served. The dinner will be purely for Royal Air Force Officers who have served in Iraq since the Armistice, and admittance will be by ticket only. Air Marshal Sir John Salmond, K.C.B., C.M.G., G.V.O./D.S.O., has kindly consented to take the chair, and Air Commodore A. E. Borton, C.B., C.M.G., D.S.O., to act as Vice-Chairman. Tickets, 12s. 6d., exclusive of all wines, on application to R.A.F., Iraq Dinner Committee, A. and A.E.E., Martlesham Heath. Gordon Bennett Balloon Race THE Royal Aero Club will be represented by three com- petitors in the Gordon Bennett Balloon Race at Brussels on Sunday, June 7 next, as follows :—Mrs. John Dunville's " Banshee III " (80,000 cub. ft.) ; pilot, Lieut.-Col. John D. Dunville or Squadron-Leader F. W. Baldwin. E. Allen's " Elsie " (80,000 cub. ft.) ; pilot, Capt. J. F. Johnson or Commander F. L. M. Boothby, R.N., and E. Allen. Mrs, Arthur Spencer's " Miramar " (80,000 cub. ft.) ; pilot, Capt. C. W. Spencer or Capt. C. W. Berry. British Empire League AIR VICE-MARSHAL SIR W. S. BRANCKER and Mr. Alan Cobl.am will be entertained to luncheon by the British Empire League, on Thursday, May 21, at the British Empire Club, in connection with their recent flight to Rangoon and back. Major-General J. F. B. Seely will preside. The Royal Air Force Memorial Fund A MEETING of the Grants Sub-Committee was held at the offices of the Royal Air Force Memorial Fund, 7, Iddesleigh House, Caxton Street, London, S.W.I, on Thursday, April 30, the following members of the committee being present : Lieut.-Commander H. E. Perrin (Chairman) ; Mrs. L. M. K. Pratt-Barlow, O.B.E. ; Mr. W. S. Field ; Squadron-Leader E. B. Beauman. The Committee considered 18 cases of appeals for assistance, and made grants amounting to £103 Is. 6d. The " R.E.P. Joy-Stick " Claim IN connection with the famous " R.E.P. Joy-Stick" case—to which we have previously referred—it is an interest-ing fact that the first patent in the world for a single-stick aircraft control was granted to a British subject in 1906, namely, A. V. Roe. The difference between Enault-Pelterie's patent and Mr. Roe's was very slight. M. Enault-Pelterie was claiming something in the neighbourhood of £1,000,000 from the British Aircraft Constructors for using his invention, but the Paris Court non-suited him. It was decided that Mr. Roe was merely acting as the agent of the British Govern- ment, which ordered aeroplanes provided with " joy-sticks," and as a foreign Government cannot be sued in the French courts, the suit must fail. 279
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