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Aviation History
1937
1937 - 1114.PDF
SUPPLEMENT TO FLIGHT 420/1 23 THE AIRCRAFT ENGINEER APRIL 29, 1937 that the lift be taken as proportional to the chord. By so doing, it is possible to work out the tail characteristics quickly and with fair accuracy. The slope of the lift curve with floating elevators (at) is given by 1 a, !0 9 8 7 6 5 4 3 •> FIC 3.8 SLOPE OF LIFT CURVES OF RECTANGULAR WINGS OF DIFFERENT ASPECT RATIOS. II 1 ^vv 'Equivalent Monoplane asf. 1 ' 1 4H '; LotA* . 0.66 1 1 - a 0 • 2-83 I Mean) pe r radian a \ )ect ratio • Slope of lift 1 •urve 1 / / i / V 1 *iE e Si .25 SE where e = .25 — .4Z2 where ST = Tail plane and elevator area SE = Elevator area. — a2 1 b1 »i — '"5' ~ TABLE : FOR VALUES / = 0.10. E .03 .06 .00 .10 .15 .20 .30 .40 .50 .60 .70 a2 «1 .133 .212 .273 .294 .376 .447 .371 .671 .758 .832 .881 - h (E) .1-2:1 .181 .218 .229 .265 .280 .288 .265 .220 .176 .121 CP .237 .225 .2135 .209 .1895 .1695 .131 .094 .057 .021 -.009 fi .584 1.452 2.421 2.77 4.71 7.08 13.29 22.28 37.10 61.80 117.80 £5 19.45 24.2 26.9 27.7 81.4 35.4 44.3 55.7 74.2 103.0 154.0 1-4 1-5 1-6 1-7 1 1 1 1 1 I 1-8 !-9 2-0 2-1 2-2 2-S 24 Per Radian -i—I •025 •033 0J5 Per Degree 040 A summary of the results of the previous article is given below :— KL = axa.t + «2Ti where at = incidence of part ahead of hinge 7] = angle between elevator and fixed portion. Km0=/W -A(E) where f(f) = i — 4.9^ A(E) = - (1 - E) VE(i - E) + .0036E + .0453 (1 - E) CP 1 6, 1 .1 — = 1 — /,(E) fit) with elevators free. e -25*1*1 57-3 The CP (floating elevators) for small values of E is given approximately by CP — = x - 1-54 E It is the exception rather than the rule for the elevators to extend over the entire span of the tail plane. If we accept the uniform loading assumption the slope of the lift curve with floating elevators becomes 1 1 • a,— 1 (1 -*,•-• ~ ST SE «i ' .25 SE/ST «! ' .25 where SE = elevator area ST = total tail plane and elevator area and J2 = E£i- Where the tail is tapered the value of E for reading off the graphs is taken at the mid point of the semi-span of the elevators. REFERENCES 4. A.P.970. 5. N.A.C.A. 458. " Relative Loading of Biplane Wings," Walter S. Diehl. 6. N.A.C.A. 501. " Relative Loading of Biplane Wings of Unequal Chord," Walter S. Diehl. 7. " Aerofoil, and Airscrew Theory," H. Glauert. 8. N.A.C.A. 539. " Investigation of Full-scale Split Trailing-edge Wing Flapi with Various Chords and Hinge Locations," Rudolf Wallace. 9. Aircraft Engineer, October, 1935. "The Characteristics of Plain Flaps" W. R. Andrews. TECHNICAL LITERATURE SUMMARIES OF A.R.C. REPORTS R EPORTS published by His Majesty's Stationery Office, London, which 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 booksellers. A COMPARISON OF THE DRAG OF TROUSERED AND RETRACTABLE UNDER CARRIAGES. By R. Jones, D.Sc, A. H. Bell and A. F. Brown, B.Sc, erf the Aerodynamics Department, N.P.L. R. & M. No. 1651. (6 pages and 5 diagrams.) February 3, 1936. Price is. net. The experiments described below were conducted at the request of the Aero nautical Research Committee on models kindly provided by the de Havilland Aircraft Co., Ltd. It was desired to obtain typical figures for the drag of a trousered undercarriage and to estimate the gain that would result if the undercarriage were completely retracted. The best way to obtain the required data was to mount two nacelles on a standard aerofoil, .first with the undercarriages pf the trousered type attached, and secondly faired as they would be with a retracted undercarriage. The difference of drag could thus be obtained in the presence ol a wing,- thus closely representing the practical problem. 1 , The experiments were conducted over a range of incidence in the Compressed Air Tunnel at values of R of 0.3 and 4 millions approximately. The addition of the nacelles results in a decrease of kLmax. of about 7 to 10 per cent., with a change of about 0.8° in the no lift angle. The drag of the wing, nacelles, and trousered undercarriages is 65 per cent, greater than that of wing and nacelles, at a high Reynolds number. NOTE ON THE STRUCTURE OF TURBULENCE IN A NATURAL WIND, CONTAINING ALSO A DESCRIPTION OF A SENSITIVE PRESSURE GAUGE. By A. Graham, M.Sc, D.I.C., of the Royal Aircraft Establishment. R. & M. No. 1704. (16 pages and 11 diagrams). January 24, 1936. Price 2s. 6d. net. In order to extend knowledge of the structure of a natural wind the pressure fluctuations from a Dines head, mounted on the top of the wind tower at the National Physical Laboratory, were analysed by a Photo-integrating method to determine the frequency distribution of gust velocity. These experiments are described in this report together with a description of a sensitive diaphragm pressure gauge, of general utility, which was developed for the experiments. The structure of winds prevailing at the time of the experiments having mean velocities between 10 and 15 ft./sec. was analysed and it was found that the frequency distribution of gust velocity follows very closely the normal error law. The diaphragm gauge appears to be a satisfactory instrument for recording and measuring continuous,, small and rapid pressure fluctuations. A SUCCESSIVE APPROXIMATION PROCESS FOR SOLVING SIMULTANEOUS LINEAR EQUATIONS. By J. Morris, B A., A.F.R.Ae.S. Communicated by the Director of Scientific Research, Air -Ministry. R. & M. Ko.- i/ii. (12 pages.) November 1, 1935. Price 2s. net. Simultaneous linear equations of three or more variables are commonly trouble-' some to solve numerically. This report describes a successive approximation method of solution which has been developed as a result of work on the simultaneous equations arising in structural problems. The process is essentially a tabular one based on the iteration principle. A detailed description of the procedure is given by reference to full examples and^ the conditions governing the convergence of the process are discussed. Certain' special devices for the treatment of difficult cases are also mentioned. The process is found to be of practical value, particularly for the treatment of a system of simultaneous equations in which the coefficients of the unknowns in the principal diagonal are large compared with the other coefficients. Such systems of equations are common in structural problems.
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