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Aviation History
1911
1911 - 0298.PDF
r/ucHT) APRIL I, 191 I. PROBLEMS RELATING TO AIRCRAFT. By MERVYN O'GORMAN. Continuedfrom page 266.) 42- Massing the Weights near the Centre of Gravity.— There are reasons for keeping the moment of inertia of the aeroplane round its centre of gravity as small as it possibly can be kept, and we must not attempt to improve on the effects above indicated, by spreading the weight to add to the inertia of the wings for example, otherwise we shall soon find trouble which will far outweigh these small advances towards stability. 43. One more suggestion is to free the two main wings so that they can bodily flex or hinge upwards to a limited extent; and to connect each wing by a pull wire to an aileron at the other side. The object of this arrangement is that, if a local gust lifts the right wing, its movement upwards shall, by pulling the Fig. 14.—Showing the contrast between the sections of a spar of a British-made Farman aeroplane and a good fair shape for ^dirigible work. The eddy caused by the spar will be considerable. left aileron down, thus throwing down more air on the left, at once lift the left wing to a corresponding degree. The movements should be nearly simultaneous so as to avoid a delay during which equilibrium may be lost sufficiently for the man to become aware of it; the mere flexing upwards of the whole of the right wing in itself, apart from the control of the opposite aileron, conduces to stability, since this movement reduces the effective supporting area, and alters the direction of its reaction. 44- Head Resistance.—The one essential improvement which we require in aeroplanes, other than in stability, is the diminution of their head resistance. To make the idea graphic at once it is only necessary to state that during certain periods the average w nd over large portions of the globe, including parts of the British Isles, is reputed to move slightly (i.e., at an angle of 40) upwards ; if therefore we could reduce the head resistance of our aeroplanes till their gliding angle instead of being 8° were 20, we could often remain in the air like birds supported by the wind, fluttering, perhaps, from point to point to keep in the upstream, but still acquiring a totally new advance in the art of flight. Progress in connection with the diminution of head resis tance can only be made by an extremely slow process, namely, the detailed study of every individual organ and part. It is a double investigation—we require to sacrifice nothing of strength—yet we must gain all that can be taken away of head resistance. 45- Spars.—All spars at present in use have a section which is more or less fair shaved, but if we compare them to the shape found to give the minimum head resistance for irigibles we get the contrast shown by Fig. 14, in which the spar section appears much too fat for its length, and has the maximum diameter too near the middle part. We want to know as a certainty (for we already suspect it strongly) that ® ® Invention During 1910. AERONAUTICS are still most prominent in the field of inventive activity, according to the annual report of the Comptroller-General of Patents. It states that efforts are now being mainly directed towards perfecting the details of aeroplanes, such as the balancing, controlling and landing devices. But, in addition, the development of the science is making itself evident in other fields of invention. One of less head resistance and weight would be involved by making larger spars of better form and fewer in number. When, however, we begin to give to the spar an appreciable depth, C, D, the fin effect of this will react a little upon the steering quality and stability of the airplane in gusts, and this must be tested before any statement of the utility of such an alteration can be made. 46. It does not necessarily follow that the airship form, having the maximum diameter at F, E, is the best for struts, but at any rate one machine which has a notably good gliding angle adopts these thin-shaped spars—I mean Mr. Cody's— which is often careering about Laffan's Plain and Farn- borough Common. I have pleasure in thanking him for the several occasions on which I have been his passenger. 47. Curved Planes.—The total skin frictional resistance of an aeroplane is about 10 per cent, of the whole resistance, and in investigating the subject it seemed advisable to study the form resistance carefully, and above all the lift, drift, and movement of the centre of pressure for various inclinations of each. Thus a series of aeroplane curves linked together by some common mathematical quality was necessary before any intelligent sequence could be given to a series of experi ments. Supposing one has got a set of equations which include all the curves of all known aeroplanes, [and I will show how this may be done,] we may proceed as follows — Make a model according to any selected equation, conduct a quantitative experiment upon it, and repeat this experiment on other models whose equation differs from the first by one variable only. Plot the curves and find the minima and maxima desired. 48. I do not propose to enter into any details of the ex perimental investigations, but the equation method is as follows:— After many hours of assiduous " trial and error" and plotting work at various times by Mr. W. C. Claypole, Mr. John Damon and Mr. Watts, we found that the head equation of any such shape can be given by a curve of the form aym — x" (x- A)'* (Equation A.) while the trailing end is given by another curve of very similar equation, viz. x" (x - tf (Equation B.) with very little trouble these two curves are made to meet and osculate at a point of maximum rise. An investigation of these equations shows that— The constant a determines the rise, The constant b determines the chord, While m determines the quickness of curvature of the curve, And n the position of the maximum camber. 49- The Effect of Varying m.—If m increases the leading edge becomes bluffer, i.e., bluntly curved down ; if m' in creases the trailing edge becomes bluffer, i.e., bluntly curved down ; but the effect of m is always more marked because of the forward position of the maximum camber. For a value of m' = 1 the trailing edge becomes cup-like and lies parallel with the chord, but a smaller value of m can usefully be employed for the leading edge curve. SO. The Effect of Varying n.—In practice the position of the maximum ordinate of the curve-—i.e., the maximum height of the camber is distant from the front of the plane from 25 per cent, to 35 per cent, of the length of its chord. Now it can be shown that if this percentage is expressed by p, then^ = 33'33« ,718B (Equation C.) when n is the exponent of x in Equations A and B above. For instance, if n = o-68, then the maximum camber occurs at a point one-fourth of the distance along the chord. If the maximum camber is required one-third of the way along, then n — 1, and the Equation A becomes expression ay™ = x (x - 6fi (To be continued.) ®^ ® the'most striking examples of this is seen in the increase in the number of internal-combustion engines adapted for flying machines, particularly in those engines having revolving cylinders. Aeronautics have also made possible a new mode of attack in time of war, and to meet this danger inventors have been giving much attention to guns and projectiles suitable for destroying aerial craft. 300
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