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Aviation History
1914
1914 - 0176.PDF
FEBRUARY 14, 1914. Edited by V. E. The Dependence of Aviation on Model Aeroplane Work. By F. HANDLEY PAGE. (Concludedfrom page 128.) Now that I had a suitable design of a model upon which to ex periment, and had made all the necessary arrangements for testing it, it was neces«ary to plan out a proper scheme of tests to be carried out on these models to obtain the data that was required. In these experiments the lifting capacity of the planes as well as the itability effects obtained, bad to be tried at one and the same time. There were made up many types of planes; some of them of the type which wr are making at the present time, and others with the ordinary square ended planes, in this case the model being provided with a tail. The best results which we obtained were with the plane of the type similar to the present one. Here it is necessary to give a word of warning to the experi menters. It is necessary when comparing results on different types of planes that the standard of workmanship should be exactly the same on each model. If not there is the probability that the model which has the inferior aerodynamical qualities may prove the better flyer owing to its being made better. It is necessary, there fore, to most carefully examine the models to see that each has been made as well as possible. Turning now to the results which were obtained with these model experiments, it was found that if the plane ends were swept back far enough, and there was a sufficient difference of angle between the tips and the main lifting portion of the plane, the model was very stable fore and aft. The reason for this is very easily seen if you refer to the Turnbull experiments of which I have already told you. The centre of pressure moves forward when the angle decreases, and backward when the angle increases, as found by Mr. Turnbull with his plane of double curvature. With a plane of single curvature with the concave side facing downwards, the centre of pressure moves backwards up to an angle of from 15° to 20", and thus there is a change in the results and the centre of pressure moves back again. It is necessary with this type to employ a tail so as to obtain the same movement that the centre of pressure has with a plane of reverse curvature. It is most important when designing a plane with a reverse curve that the negative angle of the rear portion should be exactly right both in length and angle, otherwise there is a tremendous loss of efficiency. This required amount it is only possible to find out by experiment. In carrying out these experiments, we found many things that were not necessary in the planes which we had originally fitted to the models, and that to obtain the best results as regards stability and lighting power, certain curvatures and so forth had to be used. So far I have dealt mainly with the lift experiments on the models, but when the plane was found that gave the best lifting result, it was then that the second problem had to be dealt with—namely, that of stability. In this connection a great many devices were tried with vertical hns placed at different points on the longitudinal axis of the model, mainly with a view to damping out lateral oscillations. It was found that if the plane had a sufficiently large " wash out" and was thick in the centre, a vertical fin between the planes was not necessary. A vertical fin at the tail, of the proper dimensions, was exceedingly useful for keeping the machine facing the wind, and with this small adjustments could be made, and the machine kept on a stiaight course. I have taken this experiment as an illustration of the way in which tests may be carried out to obtain certain definite data to full-sized rnaenmes. They form, when the designer does carry them out, most useful supplementary work to the research wOIk which is now carried out in wind tunnels in the laboratory. In this connection it is very interesting' to note, that with the composite plane upon which I experimented, the centre of pressure ound in he model experiments came at exactly the same point as £ri,»^, CentIe°f ?reSSUre on the Pl««. found by dividing the plane into a series of sections, and for the angle at which the result"* y'ng determmmg its <*«» of pressure from wind tunnel From the model experiments was constructed our first full-sized machine, which was known as the " Blue Bird," it havine been !?Cn H** »'Ue ^ Jhe " Blue Bird" ™ followedV „e JS ?J!lf P>, i0^d bCCaUSe the ffiachine fcU t0 P«ces ; then came another to which no name was given; following it was the "Antiseptic," named by the late Mr. Edward Pet*, owingTo the JOHNSON, M.A. machine having been painted with a non-rusting paint Then there is our old 50 h.p. monoplane, buiit in 1911, and still flying, known as the "Yellow Peril." . I should like to give you some suggestions as to the way m which your future model work might be extended so that experimental results of value might be obtained. There is probably not very much more progress to be looked for in the improvement of the lifting capacity and the diminution of resistance of ordinary planes. Experiments have been, and are still being, carried out all over the world, and plane sections have been evolved which have lift drift ratios of very high value. It is pro bable a maximum of one in twenty to one in thirty will be reached shortly. There are, however, great improvements to be effected as regards the stability of machines. It is the carrying out of tests for the improvement of this feature of machines that should call your attention for the coming year. It is a subject that can only be properly dealt with by model flying tests, and it is one therefore that should demand your closest attention. There seems to be a particular way in which machines of the uture may develop. The modern efficient flying machine will have to be efficient, travelling at a high speed, and capable of a wide speed variation, and to obtain these results to the fullest effect the propeller will have to be placed in the rear of the aeroplane. To understand the reasons for this, let us consider how the power required to drive the aeroplane through the air is split up. Part is used in overcoming the resistance of the planes to their motion through the air, and the other part for that of the body planes. No matter at what speed you fly, planes for a given lift will have approximately the same resistance, provided that they are designed to fly at their most efficient angle at this speed. It is, however, different with the body resistance. Even if the fuselage is most carefully streamlined, and pilot, passenger, and engine, &c, all carefully enclosed, yet the higher the speed at which it is driven through the air, the higher will be the resistance which has to be overcome. The characteristics of a slow-speed machine will be that the largest proportion of its power will be necessary to drive the planes through the air, whilst in the high-speed machines the power will be required for the body. In the slow-speed machines, the pro peller blowing in front upon the fuselage increases its small resistance a negligible amount. In the high-speed machine the body resistance, already a serious item, is increased considerably if the propeller is placed in the front of the machine. It will pay them to place the propeller in the rear in the high-speed modern machine, just as it pays in a steamship, where the whole of the resistance is the body and wave making resistance. From the point of view of Naval and Military requirements, the propeller behind the machine is much the better type. It offers such splendid opportunities for observation or for firing a gun. From the point of view of both efficiency and service, the propeller- behind machine scores every time. There are many ways in which a propeller-behind machine may be made :— 1. As in the Maurice Farman machine, with a tail boom and out riggers surrounding propeller. 2. As in the Paulhan Tatin or the old Petre aeroplane, with the propeller at the extreme end of the fuselage. 3. With the split type fuselage and the propeller revolving on one of the fixed tail booms, as in the Grahame-White Military aeroplane shown at the Olympia last year. 4. With a tailless plane and swept back wings. In the Farman machine the increased efficiency obtained by the propeller position, is to a large extent nullified by the large re sistance of the rear frame-work exposed to the air. This type is also not quite so easy to handle when built for hydroplane work as a. fuselage machine. The second type with the propeller at the tail has a large moment of inertia owing to the heavy tail shaft, and is weak constructionally. The propeller position necessitates the tail being a long way off the ground, and this leads to an increased length of chassis struts with a consequent increase in resistance. Type 3 is also very weak mechanically, and heavy. Type 4 would appear to have the best future, as there is nothing in the rear of the propeller to detract from its efficiency, and it is a type which has good longitudinal and lateral stability. It is, there fore, in this direction that I think progress will be made. 76
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