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Aviation History
1914
1914 - 0693.PDF
JUNE 26, 1914. Edited by V. E. The Use of Models in the Development of the Aeroplane. (Concludedfromp. 666.) Where the Present-day Aeromodellist has Failed. Now it is just here, it appears to me, where the present-day aero modellist has failed, failed signally, though let us hope not disas trously, Aeromodellists, generally speaking, do not appear to have kept either accurate or scientific records of their experiments. This may be, of course, a gross libel, I should only be too pleased to know it was such. Even supposing they have done so, there has certainly been no general pooling of results. Now if the model is to be worth anything from a scientific point of view in the future, it will not be by each experimentalist ploughing his own lonely furrow, but by a number of real workers and enthusiasts combining together to carry out a certain series of experiments with some useful and definite end in view. By useful and definite end I mean some point on which designers and builders of full-sized machines desire further practical knowledge, which knowledge it appears at least) highly probable can be obtained from careful and accurate experiments carried out with models. Full-sized Workers and Modellists must meet. For this to beome possible, it is an obvious inference that full- sized workers and model workers must meet and discuss matters ; so far but little has been done in this way ; but a beginning has been made, with, I am very glad to be able to say, the most happy results. Each found the other had knowledge unknown to both, and more than one full-sized worker has afterwards quite frankly confessed, that he felt quite sure he had gained as much knowledge as he had given. Personally, I regard this intercourse of the two parties as essential, if the model is going to play any part in the future development of the aeroplane. One result of such an intercourse will undoubtedly be for the full-sized man to think more of the model and the model man to think less, with, I am sure, the most happy results to all concerned. Where the Model Scores. The model scores most heavily, of course, on the score of expense, and from, the fact that such experiments can be carried out without danger to human life. In days of adversity, of depleted exchequer and other antagonistic circumstances, the full-sized worker not un naturally casts his eyes on the model, and is prone to ask himself the question : Is this thing any good ? Or it may be that he has at last become convinced, through circumstances into which it is not necessary to enter, that experiments with models can be applied successfully to full-sized work ; with the result that his one regret is he had not made more use of such experiments and thereby very possibly saved himself or the company, whose real head he is, thousands upon thousands of pounds. The Scientific Model. For well over two years I have carried on in FLIGHT a campaign on behalf of the scientific model: a campaign which I am glad to say is I think at length beginning to bear fruit. Now what do I mean by a scientific model? I mean several things, and I do not of necessity mean the same thing now that I meant last July or that I may mean next August. A rubber-driven machine built solely for either duration, distance, altitude, &c., is not what I should term a scientific model; it is a scientific toy, that is all. Now there is all the difference in the world between a scientific toy and a scientific model. It does not matter how much scientific knowledge you may cram into your toy, not even if, as I once heard someone say, " It be fair burstin' with it," it is still only a toy. It is a toy because its design is such that it cannot by any stretch of the imagination be applied to fall-sized design. Such machines are absolutely useless to full-sized designers or for real scientific experiments, experiments, i.e., which can be usefully applied to mil-sized work. I do not say they were not or could not have been of use in the past, but that is gone, and their chance in this respect has been, practically speaking, lost. We must give up our single sticks, our celebrated A frames, and many other of our most cherished constructional items if we are to build a machine to which the term MODEL can be in any way truth fully and justly applied, and if we do not experiment wilh models of what use considering at all the question, " The Use of MODELS in the development of the Aeroplane " ? Our competitions also must be so arranged that they both can and will be won by real models 693 JOHNSON, M.A. and not flying-sticks, no matter however well designed, constructed, and full of science they may be. Our model aviation knowledge of to-day is far in advance of what it was two or three years ago ; there is no need, no necessity what ever to build 6uch a type ofmachine to get it to fly. Quite good flights can now be obtained with machines to which the term model can with some truth be applied. By quite good flights, I mean flights of half a minute and upwards, and a flight of half a minute even is quite long enough to make a scientific observation, more especially if 50 such flights be made and the mean result be taken. 7*he Type of Model Experiment that is wanted. We especially want experiments with models fitted with covered- in fuselages of the Canard type, with tailless models of the Dunne type, with models of such a design as to be suitable for military purposes, fighting aeroplanes, capable of firing astern as well as ahead, with models of the combined airship and aeroplane type, a type whose total weight is somewhat heavier than air, but which is capable of rising and flying when propelled through the air at a low velocity. We also want experiments with models carrying, say, small toy cannon, or such like device, and capable of firing them whilst in actual flight in order that we may observe the effect of the gunfire on the model's stability, course, &c. We also require, perhaps, above all things, a hydro-aeroplane which can arise from and alight on the surface ol really rough water. Model experiments could undoubtedly help us here, although 1 am afraid in this caie the model would have to be a large one driven by a petrol motor. The foregoing are only a very few of a long list of experiments that could be carried out wilh considerable gain to aviation work generally. Model Research Work. No real distinction, no hard and fast line can very possibly be drawn between investigations made with what I have termed the scientific model and model research work ; save that much of the latter is generally carried out in the laboratory, and is very frequently confined to some portion of the machine in model form, and not to the machine as a whole. Such research work is generally carried out either on a whirling table or in a wind tunnel, generally the latter, the circular course of the former being obviously a greal drawback, and for anything like even fair results necessitating a very long arm. The great advantage of the wind tunnel is that by means of having the model stationary and the air travelling past it, you can, by having a glass window in the tunnel close to the model observe very carefully and accurately what is going on. Its chief disadvantage is that it must be of very large size in pro portion to the size of the model if really accurate results are desired, which necessitates a powerful and expensive motor if the air is to be moved through the same at a high velocity. And it is experiments in winds of comparatively high velocities that arc so much needed. Another manner in which such a problem could be tackled is by propelling or drawing such a model along a long wire or aerial line suitably supported at a high velocity. The model would have of course to be fitted with suitable self-recording instru ments. In the writer's opinion not nearly enough use of thin method has been made. Another method of attacking the problem would be by fitting a suitable attachment to a swift motor car. This latter method would have the great advantage that the model or part model experimented on would lie under personel observation all the time. I'roblems of stability appear to be most suitably studied in actual free flight. If we except the model research work which has been carried out at the National Physical Laboratory, at a few technical colleges, and by some private individuals, but little work of this character has been carried out in this country. Such work, I am sorry to say, does not appear to appeal to the average aeromodellist in the least; in fact, you have only to bring up the subject, for him to look round for some avenue of escape. If you tell him that if the pro bable error in any single observation is 10 per cent, then at least 100 observations are necessary to reduce the probable error to I per cent. ; that is quite enough, he wants to hear nothing more. Where Model Experiments are so often at Fault. And yet it is just in this very respect that ordinary model ex periments or deductions are so often at fault. The observation itself and the consequent deduction may have been quite all right so far as they went; but the data, the number of the experiments made
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