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Aviation History
1926
1926 - 0128.PDF
SUPPLEMENT TOFLIGHT 22 THE AIRCRAFT ENGINEER FEBRUARY 25, 1926 By making use of Simpson's First Rule, we can now find all we require. A = area of section. I = least moment of inertia of section, h = corresponding radius of gyration. I f 30 2/5 + 2/7 + 2/9) + 2 yt + yt + 30= 57ri4(2/l 3 + 2/3S + ?/53 + 2/73 2(2/, k = A / i_/I ' AIf required, the greatest moment of inertia may be found in the same way. In this ease, the neutral axis is drawn perpendicular to XY through the centre of area of the section. This lies on XY, its distance from the nose X being x, where I /4 (?/i + 3y3 + oyb + 1y, + 9y9) x ~ 10 \4 (y1 + 2 2 2 2) y6 + Syg) + oyb + 1y, 2/5 + 2/7 + 2 (2y, 2/9) 4j/4 + 2 (2/2 + 2/4 + 2/e + 2/») To some, at first sight, these expressions may appear a little cumbersome, but the cubes can be looked up in a table, and the rest involves no higher mathematics than a little addition, multiplication, and division. For standard stream-line struts these expressions may be further simplified, as for any particular thickness of strut, the values of yx, y2, ya, etc., remain the same for every fineness ratio. Giving the symbols I, t, F, A, I, k, and a: the same meanings as before :— Z =--F* For standard stream-line struts :— yx =0-375/ yz =0-475* 2/3=0-5* y, =0-19* The tail is rounded off, the radius being 0-l<. We now get :— A = 0-725Ff2 I =0-044Fi« h = 0-246* x =0-449F* If these values are plotted for a number of values of t, and such values of F as are being used, the required dimensions of a section for any value of A, I, or k can be read off at once. TECHNICAL LITERATURE. A.R.C. REPORTS. INTERNATIONAL TRIALS. REPORT ON AEROFOIL TESTS AT NATIONAL PHYSICAL LABORATORY AND ROYAL AIRCRAFT ESTABLISHMENT. R. & M. No. 954 (Ae. 173). (46 pages and 7 diagrams.) May, 1925. Price 2s. net. Acting on a suggestion made by the Director of Research, the Aeronautical Research Committee decided in March, 1920, to institute comparative model tests in as many as possible of the aerodynamic laboratories of the world. It was thought that such tests, in which the same models would be tested successively by all laboratories, would supply valuable information which had not previously been available. The aim of wind-tunnel experimental work is to obtain reliable estimates of the forces which would be experienced by bodies moving at specified speeds through still air of infinite extent; but in practice it is necessary to hold the model stationary and to generate a flow of air past it, and measurements made in this way are in some degree open to question, in that the forces imposed upon the model may be affected (1) by the limited extent of the air stream in which they are placed and (2) by the turbulence which can never be entirely eliminated. The results must, furthermore, depend to some extent \ipon the methods adopted for con- necting the models to the measuring apparatus. Different methods are adopted in different countries, and wind tunnels of varying size and design are employed ; thus there is some uncertainty as to the extent to which a comparison can be made, c.y., between different aerofoils tested in different countries, and this uncertainty, it was thought, would be reduced if comparative figures were available from tests upon the same models. The tests finally decided upon included the determination of lift, drag, and C.P. for a standard aerofoil model of R.A.F. 15 section at various angles of incidence. The tests carried out in Great Britain are reported in the present paper (R. & M. 954), and the results plotted in the appended figures. The results should be of general interest to all establishments or firms which use wind tunnels for making experiments on aerodynamic models, and they show the amount of varia- bility that is obtained between the results on the same model tested under a variety of conditions. In general, the agree- ment between the N.P.L. and the R.A.E. wind tunnels may be considered satisfactory with the exception of one of the N.P.L. wind tunnels, namely, the 7-ft. No. 1. It is further to be noted that the results on the 4-ft. tunnels, when corrected for tunnel-wall interference by the Prandtl theory, are in very good agreement with the 7-ft. tunnel results except in the case of the N.P.L. 4-ft. No. 2 tunnel. THE LATERAL CONTROL OF STALLED AEROPLANES. GENERAL REPORT BY THE STABILITY AND CONTROL PANEL. R. & M. No. 1000. September, 1925, 2s. net. The problem of obtaining adequate lateral control of aeroplanes has occupied the attention of research workers and designers for a number of years and it is now certain that the problem is sufficiently understood to permit of a satis- factory solution in the case of the normal design of aeroplane as it is known to-day. The existing form of lateral control is the aileron, which introduces a moment tending to turn as well as to bank the aeroplane, and some device has long been needed which would give the required rolling moment without the accompanying yawing or turning moment. The most satisfactory means yet devised for obtaining this type of control is the slot-and-aileron described in R. & M. Nos. 916 and 968. Smaller improvements in other directions have resulted with the use of increased rudder control, the full- scale tests of which are described in R. & M. No. 972, and by the use of differential ailerons as described in II. & M. No. 964.. The present report commences with a general statement of the problem of the lateral control of stalled aeroplanes,, and outlines the general principles of satisfactory control. The data required and the methods of analysing the data- obtained from models are next discussed in some detail, and an account is given of certain step-by-step calculations made for the motions following from certain initial disturb- ances. The various devices tried for the improvement of lateral control are also described in some detail, and complete references are given to the whole of the work bearing on the investigation. The object of the Aeronautical Research Committee in initiating the experiments here discussed has been to reach a thorough understanding of the principles governing controL of stalled aircraft in any circumstances, and to lay the foundations of precise information upon which can be built up routine methods of predicting, from an inspection of the design, the degree of controllability to be expected in. any aeroplane. It is considered that the first of th?se 110;
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