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Aviation History
1933
1933 - 1330.PDF
SUPPLEMENT TO FLIGHT 92 DECEMBER 28, 1933 THE AIRCRAFT ENGINEER if substantiated, should greatly affect the design of wings tapering in thickness ratio along the span. The Kr for the reflexed sections on Fig. 19 shows max " that there is no p-ain in KL over that of the ° max symmetrical section. The sections given are in the region where the sym metrical sections showed instability at the stall. There is no suggestion of this instability with the reflexed sections. So much for maximum lift, and now the slope of the lift curve will be investigated. Fig. 21 shows the dependence of dK^/dx upon the cube of thickness ratio t. The laws to the curves drawn are given on the graph, and an average value covering the whole series is *** (13) 0-0506 - 5-65 t3 dx The valuation between the slopes for the different series does not appear to be systematic, so that the above generalisation is all that can be done. The next item is the point of minimum profile drag. The value of KL at the point of minimum profile drag is designated at KL opt. In Ref. 2 curves for the 43—63 and the 45—65 series were given; these are reproduced here, together with that for the 44—64 series, but based on the N.A.C.A. definition of camber—Figs. 22, 23 and 24. It is noticed that for the latter the curves drawn all pass through the zero and the law to the curves is KL opt = (6-6 - 25 t) y (14) This indicates that the value of KL opt for a section of no thickness is 6-6 y as compared with 2TCY given by the theory of thin aerofoils. Expressing KL opt as KL opt = (y + K) (A - B <) 1) (15) as in Ref. 2, then K, A, B and D have the values given by the following table. TABLE 13 K A B D Maximum Camber at:— 0-3 Chord 0-4 Chord - 0001 9-7 33-9 + 01 0 6-6 25 0 0-5 Chord - 0-05 8-0 33-3 + 001 The choice of the constant is left to the individual until more information is available. The final estimation of profile drag is then made as shown in the previous article (Ref. 2). TECHNICAL LITERATURE SUMMARIES OF AERONAUTICAL RESEARCH COMMITTEE REPORTS These Reports are published by His Majesty's Stationery Office, London, and may be purchased directly from H.M. Stationery Office at the following addresses: Adastral House, Kingsway, W.C.2; 120, George Street, Edinburgh; York Street, Manchester; 1, St. Andrew's Crescent, Cardiff; 15, Donegall Square West, Belfast; or through any Bookseller. WIND TUNNEL TESTS OF AEROFOILS R.A.F. 38 AND 48. By K. W. Clark, B.Sc., D.I.C., and W. E. Wood, B.Sc. Communicated by the Director of Scientific Research, Air Ministry. R. <fc M. No. 1543. (6 pages and 6 dia grams.) May 27, 1933. Price 6d. net. The lift, drag and pitching moments have been measured on 8 in. x 48 in, monoplane aerofoils from no lift incidence up to 40° in the No. 2 7-ft. tunnel at the R.A.E. The speed of test was 80 ft,/sec. up to the stall and 50 ft./see. beyond. The main characteristics at I = 0-335 x 10° are :— „.;., i.- at no lift Aerofoil KT max. M) (L/D) max. - 0-021 20-6 H.A.F.88 .. .. 0-531 0-0058 K.A.F.48 .. . . 0 600 0 0073 - 0 022 19 6 The lift coefficients drop suddenly at the stall particularly so for R.A.F.48, the drop being accompanied by an increase in drag coefficient and a rear ward movement of the centre of pressure. THE INTERFERENCE OF A WIND TUNNEL ON A SYM METRICAL BODY. By H. Glauert, F.R.S. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1544. (8 pages and 4 diagrams.) May 24, 1933. Price 6d. net. The problem of the interference of a wind tunnel on the drag of a body has been considered by several authors (see list of references), but the subject still remains in a very unsatisfactory state. Lock's analysis', which is the latest treatment of the subject, is based on the use of a system of images to satisfy the necessary boundary conditions and on the calculation of the corresponding induced velocity experienced by the body. On comparison witli experimental results, however, it is found that the theoretical induced velocity must be multiplied by an empirical correcting factor K whose value rises from 1 • 15 for a symmetrical aerofoil section to 3 13 for a circular cylinder. The empirical curve of this factor, K, as a function of the drag coefficient of the body, rests on very slender evidence, and its magnitude casts doubt on the adequacy of the theoretical analysis. An attempt lias therefore been made to examine the problem more closely and to derive a more satisfactory explana tion of the observed phenomena. The whole problem has been reviewed on the assumption that the inter ference depends partly on the induced velocity of the current theory and partly on a wake correction, analogous to the old choke correction. Experimental results have been analysed to check the validity of this conception and to derive values of the wake correction. Apart from two anomalous cases, where the experimental results them selves are open to question, the results appear to bo consistent with the new dual conception of the interference. The effective width of the wake, affecting the interference correction, is shown to be represented by a single curve against the fineness ratio for all shapes of body. * ('. N. H. Lock. " The Interference of a Wind Tunnel on a Symmetrical Body." E. & M. 1275. (1029.) INFLUENCE OF WING ELASTICITY I*PON THE LONGI TUDINAL STABILITY' OF AN AEROPLANE. By A. G. Pugslev, M.Sc. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1548. (11 pages and 2 diagrams.) January 13, 1933. Price 9d. net. Discussions of the stability of an aeroplane have hitherto been based upon the assumption that the whole of an aeroplane may be regarded as rigid. Recent work in connection with wing flutter, wing divergence, and reversal of aileron control, however, has drawn attention to the general importance of wing elasticity and led to the suggestion that this elasticity might materially influence the stability of an aeroplane at high speeds. In the present report the influence of wing elasticity is considered in relation to longitudinal stability. Approximate expressions for the effect of wing elasticity upon each of the relevant derivatives are given and methods of evaluating the terms involved put forward. A numerical example is then discussed and, following a more general consideration of the problem, certain practical conclusions are noted. Wing elasticity will normally have upon the longitudinal stability of an aeroplane a detrimental effect, which will tend to be more or less dangerous according as the speed of the aeroplane is close to or remote from the diverg ence speed for its wings. As practical measures for the reduction of this effect, knit for the wings should be small and the torsional stiffness of the wings large. FUEL VOLATILITY AND CARBURETTER FREEZING. By W. C. Clothier, M.Sc., Wh.Sch. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1549. (14 pages and 7 diagrams.) February 7, 1933. Price 9d. net. During the course of tests in connection with the freezing of carburetters some variation between the results of tests with different fuels was noticed and it was decided to develop a piece of apparatus that would measure these differences. A laboratory apparatus in which a mixture of air and the fuel under test is sprayed on to the bulb of a thermometer, was constructed and measure ments were made of the temperature difference between the intake air and the temperature recorded by the wetted thermometer (spray temperature) for a number of fuels. The spray apparatus provides a simple method of comparing fuels on a basis of their liability to promote freezing. With care absolute measurements may be made, but for most purposes it would be better to compare with a standard fuel. The spray temperature depends on the pressure and tem perature of the intake air, and also on the humidity if this is sufficiently high to cause saturation before the final temperature is reached. Distillation curves give a guide to the relative tendency of fuels to promote freezing but the results are hot easy to interpret. The temperature at which 25 per cent, is distilled appears to be on the whole the best criterion. REPORTS AND MEMORANDA OF THE AERONAUTICAL RESEARCH COMMITTEE PUBLISHED BETWEEN APRIL 1, 1932, AND SEPTEMBER 1, 1933. R. & M. No. 1550. (7 pages.) September, 1933. Price 6d. net. Previous lists of the Committee's published papers are Reports and Memo randa 650, 750, 850, 950, 1050, 1150, 1250, 1350 and 1450. For a classitlea list of reports on sale as separate issues, with prices, see I ist B, for wnicn application should be made to H.M. Stationery Office. 1310/?
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