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Aviation History
1926
1926 - 0404.PDF
• > t j JUNE 17, 1926 INSTITUTION OF AERONAUTICAL ENGINEERS Two Papers DURING the last few weeks two papers of more than ordinary interest were read before the Institution of Aeronautical Engineers. Unfortunately, space does not permit of pub- lishing the papers in full", and for a detailed report of the papers and the discussions following them we must refer our readers to forthcoming Minutes of the Institution, in which the papers and discussions will be published in full. METAL-CLAD AIRSHIPS On June 4 Mr. Ralph H. Upson, M.S.A.E., of Detroit, gave a lecture on "Recent Progress in the Development of Metal- Clad Rigid Airships." Colonel J. T. C. Moore Brabazon, M.C., M.P., was in the chair. The Chairman said that Mr. Upson, general manager of the Aircraft Development Corporation of Detroit, was a bird of passage this time, as he only had a very few days in London. Mr. Upson would tell them of some of the new developments which were taking place with regard to airships. Some of them divided themselves into two camps over aeroplanes and airships, but if airships were a luxury in some countries, in the opinion of the Chairman they were a necessity to an empire like the British, where long distances had to be tackled and big weights and large bales carried very long distances. Mr. Ralph Upson said he regretted that his talk had been variously termed a lecture and a paper. He thought these were possibly too dignified terms for the informal talk which he proposed to give. He had heard certain criticisms of the length of time which it had taken for Great Britain to get at the actual construction of the large airships. In order that no one might be discouraged, he would say that the Aircraft Development Corporation in Detroit had been working for five years on one problem only, that of making better airships, and they had only now reached a point where they were ready to begin construction on a very small demonstration unit. The company was actually organised for the purpose of developing a type of airship which should be thoroughly safe and economical for commercial purposes. The main object of the whole development was improvement in the fireproof qualities of the structure. Helium v. Hydrogen There was, the lecturer said, a good deal of misconception as to the situation in the United States with respect to helium. Many people seemed to think that in America they had large quantities of helium. That was far from being the case, and they were still very far from having a supply of helium which either in quantity or price could be called commercial. By improvements in construction and operation it was possible to use helium in such a way that it would not be wasted to any great extent, but even assuming that there was no loss of helium at all, that it cost nothing except the initial filling, and without allowing anything for valving or fpr leaks, there were still very considerable disadvantages in the use of helium for commercial purposes. In the first place, helium was deficient in lift, and so far it had been impossible to get it in a quality which lifted more than about 90 per cent. of good commercial hydrogen. Later it might be possible to increase the purity so as to get 92 per cent, of the lift of hydrogen, but even on that figure there was a very serious decrease in the useful or paying load. Turning to the subject of hydrogen, the lecturer pointed out that the fact that hydrogen will burn, furnished at the same time one of its principal disadvantages and one of its principal advantages. The fact that it would burn made it .possible to use hydrogen as part of the fuel and so increase the range of action of the ship. In one way that was really one of the factors making for safety, because it increased the reserve cruising range, not only on account of the extra fuel that could be carried, but on account of the gas itself being useful for fuel. Putting everything together, one got as a final result that with a ship of the range and size which was now contemplated, if they wanted to make the greatest possible distance they could attain just about double the dis- tance with hydrogen that would be possible with helium at equal speed. Worked out on a basis of paying load in many cases it would be quite within the range of commercial feasibility to carry considerably more than double the pay- load with hydrogen than with helium. For commercial purposes therefore they were not at all ready to scrap hydrogen. One of the main desirable features they wanted to work out was to get an airship which was sufficiently fire- proof in its own structure to make it as safe with hydrogen as with helium. One was not afraid to ride in a motor car with petrol, providing the petrol was safely contained in a metal tank ; and one was not afraid to live near a large storage tank of illuminating gas, provided the tank was of proper construction. In the same way the metal airship should be to all intents and purposes perfectly safe for ordinary com- mercial use, whether used with hydrogen or helium. Turning to the question of how to get such an airship, Mr. Upson said it was fairly clear before they went very far that Duralumin had very good qualifications. It was "true that Duralumin corroded to a certain extent, but they were learning several practical ways to protect it. As long as the surface was protected the)' knew that Duralumin was of indefinite life. Fabric on the other hand, was affected by the actinic rays striking through any protective dope or varnish pre- paration, and the rays deteriorated not only the covering but the fabric itself. Having decided upon the use of Duralumin, one of the fundamental principles employed in working out the development to a practical point was the assumption that the covering should be made an essential part of the structure. The lecturer compared the problem to that of a steamship, in which the frames and the plating together formed the structure. A similar principle was aimed at in the construction of the metal-clad airship. When it came to the means of putting this theory into practical form, there were considerable difficulties. It was very difficult, for example, to get for the smaller sizes or even for moderate sizes of airship a gauge of material thin enough to compare with the plating of a steamship in proportion to the loads it had to carry. As a matter of fact on simple proportion it worked out as an almost prohibitively thin skin. Thus for the smaller sizes at least it became necessary to allow- a certain propor- tion of the weight for mere covering purposes. This require- ment necessitated a re-design of the entire hull in such a way that the amount of surface would be reduced to a minimum. At the time when Mr. Upson's corporation began work, it was usual for rigid airships to have a fineness ratio of between 8 and 10. That of the " Shenandoah " was 8-7 and the " Los Angeles" had a fineness ratio of approximately 7-2. Mr. Upson had an idea as had also certain other people, that with a proper design of curve it would be possible to make an airship efficient which was very much shorter and more compact than that. Just about this time the thick section wing began to come into favour for aeroplanes, and some astonishing results were being obtained, so that just by analogy they estimated that they ought to be able to design an airship hull with as low a fineness ratio as 3£. Gradually a curve was evolved which they called the E—H curve, because it was a combination of elliptical and hyperbolic curves. The one part of the curve not susceptible to analysis, i.e., the tail, was made in several differing forms of varying fineness. One was carried to an extreme point, and there were three other types that were progressively shorter and more round. The tail which was next to the shortest came out best, everything considered, and was chosen against the others. With this tail the shape evolved had a fineness ratio of approximately 2-8. The first tests were made in the Navy wind tunnel at Washington. According to these tests the hull resistance was approximately one-half of that of the " Shenandoah " hull, which had a fineness ratio of approximately three times greater. There was some doubt as to whether this figure could be accepted as reliable, but even if another 100 per cent, were added to the figure for resistance, it seemed that the lower fineness ratio hull could be made to have a low resistance. One objection to the short hull was that it was unstable. From fundamental considerations it appeared entirely reasonable to suppose that a ship of this kind could be stabilised satisfactorily, and by means of a close study of the proportions, dimensions and arrangement they had been able not only to get satisfactory stability and control, but to effect a very great improvement over anything that had appeared up to that time. They made three different styles of fin surfaces to start with, and eliminated one factor very early in the study by discovering that eight fins were very much better than four. They then gradually narrowed the problem down until they finally had the shape, size and position both circumferentially and longitudinally that gave a very close approach to the absolute maximum of efficiency. Thus by the one means of discarding the old type of fins and re-arranging them, they obtained a ship which was not only not unstable, but which was particularly good as regards 350
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