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Aviation History
1934
1934 - 1460.PDF
SUPPLEMENT TOFLIGHT 1002A n THE AIRCRAFT ENGINEER SEPTEMBER 27, 1934 its ends than in its central portion. As another example, let us consider the shortening of a bent strut of length il under an end-load P. If the strut is of uniform section, it will, under end load, tend to bend to a sine curve, if " tapered," to a curve intermediate to a sine curve and a circular arc. In the first case the bow strain coefficient is 0.616, •while for a circular arc it is 2/3. An estimate then of say 0.64 will probably be quite near enough for practical purposes. If the load bends the strut to a known camber d, the shortening of the strut will be expressed by the equation : . • " ' " /dy d* (bow strain) x -a/ = 0.64 ( %-) 2/ = 1.28 -j If d is not known, but one knows 8 the " effective "Ve initial camber*, d = — 8 approximately where Pe is the Euler load for the strut. The substitution of this value d in the preceding equation gives the shortening of the strut for any end-load P. * Approx. = the initial camber -f 1.2 X eccentricity of the neutral axis due, for example, to want of uniformity in the thickness of a tubular strut. 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; cr through any bookseller. NOTE ON A METHOD OF REPRESENTING SPAR TESTS. By H. R.Fisher, B.A. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1537. (26 pages and 16 diagrams.) Feb-ruary 2, 1933. Price is. gd. net. Professor Southwell has put forward a method* of graphical representation in which the points representing the observations iall approximately on a straight line whose slope is a measure of the load corresponding to elastic instability. It is thus possible to obtain an indication of the value of this critical load when elastic failure of the material prevents this load being nearly approached. A spar, which may have a small initial bowing, is1 supposed subject simultaneously to end load, which may be applied eccentrically, and to symmetrically distributed lateral loading. Calculations of its behaviour, made on the usual assumptions, are put in a form showing the amount of deviation from linearity of the curve obtained by plotting deflection against deflection/load,* both when the lateral load is constant and when it is kept proportional to end load. The effect of zero errors in measurements of deflection and end load are con- sidered. Experimental confirmation of the theory is obtained from tests on a steel bar within the elastic limit, and results are shown of applying the method to tests in which the elastic limit is exceeded. Below the elastic limit approximations of tlie Berry type make the method -of Reference 1 applicable to spar tests, provided the deflection is appropriately defined. The rough experimental material at present available suggests that it may also be of use beyond the elastic limit. • E.F.297. " On the analysis of experimental observations in problems of elastic stability." R. V. Southwell. Also Proc. R. Soc. (A), Vol.135,1932. ; EXPERIMENTS ON THE DISTORTION OF A STRIPPED TWO-SPAR METAL WING UNDER TORSIONAL LOADING. By D. Williams, B.Sc, A.M.I.Mech.E., and H. F. Vessey, B.Sc., A.F.R.Ae.S. Communi- cated by the Director of Scientific Research, Air Ministry. R. & M. No. 1571. (17 pages and 21 diagrams.) April 19, 1933. Price is. net. In some recent work on the elastic deformation of two-spar aeroplane wings under torsional loading, theoretical results have been obtained on the convenient assump- tion that the rite connecting the spars are rigid in their own planes and so impose on the spars the same angular displacement as the wing at each point along the span. A subsequent investigation (4) suggests that actual ribs will behave very approximately according to this assumption, and the primary object of the experi- ments described in Part II of this Report was to discover whether ribs do behave in this manner, and if not, to find the effects of their flexibility. In other words, it was desired to check the accuracy of wing stiffness calculation on the basis of the " rigid rib " assumption, by actual experiment. Good agreement between theory and experiment was obtained and the basis of the theoretical work above referred to appears to be established. PART I. MODEL TESTS. By A. V. Stephens, B.A., and J. Cohen,B.A. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1576. (10 pages and 2 diagrams.) July 16, 1932. Price gd. net. The Pterodactyl is controlled by large flaps on the wing tips, which function as elevators when moved together and as ailerons when operated differentially. There are also small rudders on either wing tip, so connected that the starboard one only is deflected when the right rudder is applied and vice versa. In the past ailerons and other wing tip controls have been found to be of little value in recovering from spins and it was thought possible that the controls of the Pterodactyl might prove altogether inadequate. The Pterodactyl exhibits unusual properties in that the ailerons are of paramount importance in establishing or recovering from a spin, whereas the rudders are in- effective. The tests show that rapid recovery from any spin should be obtained pro- vided that the pilot is able to exert sufficient force to set the ailerons fully against the spin, or alternatively to move the control column fully^ forward. The existing rudders are inadequate and an appreciable improvement can* be effected by doubling their area. SOME CALCULATIONS ON THE STRESSES INDUCED BY GUSTS IN THE FUSELAGE OF A PARTICULAR AEROPLANE. By H. H. Fisher, B.A. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 15S1. (18 pages and 7 diagrams.) January 31, 1933. Price is. net. It has been suggested that gusts may sometimes give rise to serious stresses in an aeroplane fuselage and this report describes some calculations for a particular aeroplane which have been made with a view to determining the order of the stresses actually likely to occur. A method similar to that given in R. & M. 1463» has been applied to calculate the behaviour of the aeroplane when flying fully loaded at 116 m.p.h. into a gust perpendicular to the wing-chord whose velocity increases linearly along the flight path. Curves are given showing the history of the forces in various members of the fuselage. A gust of 30 f.p.s. is not capable in the conditions assumed of adding in any member examined a load of more than 0.23 of its estimated strength. Calculations for other cases, elasticity being considered, would be very unlikely to raise this figure to as ' much as 0.5. Sudden tail forces due to irregular air motions not amenable to cal- culation would have their efforts reduced by about 50 per cent, in the front bay of the rear fuselage, because of the inertia of the rear fuselage and tail. Fuselage stresses due to gusts thus appear in general unlikely to be of serious magnitude. • R. & M. 1463. Acceleration of Aeroplanes in Vertical Air Currents. Part I, by H. R. Fisher. WIND TUNNEL TESTS ON JUNKER TYPE AILERONS. By F. B. Brad-field, Math, and Nat. Sci. Triposes, and W. E. Wood, B.Sc. Com- municated by the Director of Scientific Research, Air Ministry.R. & M. No. 1583. (6 pages and 7 diagrams.) August 26, 1933. Price 6d. net. Wind tunnel tests have been carried out on ailerons of Junker type, to determine whether this is a suitable type for use when a very high degree of balance is required. The aileron is an independent surface carried below and behind the trailing edge of the wing, giving in effect a slotted flap, but arranged so that the aileron is not shielded behind the main wing. This arrangement gives a larger rolling moment per unit aileron area than the balanced aileron forming part of the wing section. In the ^.following tests the Junker aileron has a chord width of 0.2c to give rolling moments JHJomparable with those of a Frise aileron of the same span and of chord 0.3c. The Junker type of aileron produces roughly 50 per cent, greater rolling moment per unit aileron area than a Frise balance aileron of normal type, and the moment is less reduced at the stall. The yawing moments for a given rolling moment are somewhat larger on the Junker aileron except at the stall, when they are no worse than for the Frise aileron. The ailerons may be closely balanced. AN EXPERIMENTAL STUDY OF THE STALLING OF WINGS. Aeronautics Laboratory, Cambridge. R. & M. No. 1588. (21 pages and 12 dia- grams.) December 28, 1933. Price is. 3d. net. The problems presented by the flight of aeroplanes near their minimum flying speeds are not yet completely understood. Predictions of behaviour in flight based on wind tunnel experiments have not hitherto been uniformly successful and do not explain why aeroplanes generally similar in design and having the same nominal wir.g profile may differ widely in the reputations which they acquire for behaviour, at low speeds. One cause of these difficulties may lie in variation in the mode of separation of the air stream from the upper* surfaces of the wings as incidence increases. For it is known that this separation may be either sudden or gradual and that sudden separation causes sudden changes in the air reactions, while the mode of separation mav depend upon small variations in wing form or surface rough- ness which may fall within the customary tolerances of full-scale construction. The experiments were accordingly undertaken to relate observations of turbulence above the surfaces of wings to the air reactions upon them, during the process of stalling. Measurements of lift, drag and centre of pressure, and of distribution of pressure and total head were made upon a series of wings about which the flow was approxi- mately two-dimensional. These measurements were correlated with observations of turbulence obtained by exploring the field of flow with very small silk threads attached to the points of thin wires. Observations of turbulence can give a good idea of the character of the force- incidence curve for a portion of a wing as it passes from the unstalled to the completely stalled state, and it is possible to recognise those changes of turbulence which lead to ambiguities and dicontinuities in the curves. The observations throw light on the process of the stall and the nature of scale-effect and suggest that, in certain cir- cumstances, discontinuities which may affect aeroplane manoeuvre may not be revealed in the force-incidence curves obtained, either on the model or the full scale, by methods in use at the present time. * The words " upper " and " lower " will be used with reference to an aeroplane flying in the normal manner.
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