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Aviation History
1924
1924 - 0687.PDF
OCTOBER 23, 1924 turning the machine side on to the wind and allowing the latter to get under the windward wing, owing to the very large dihedral. Mr. J. D. North said it was not that he doubted the accuracy of Dr. Rohrbach's statements, but simply that, not having seen an advance proof of the paper, he had not been able to follow step by step the logical conclusions and deductions of the lecturer. He thought the comparisons between biplane and monoplane, and the result at which the lecturer had arrived as regards the relative efficiency of the two types, required qualification. He would like to know in what way the in crease in wing loading was brought about, whether by altering the span or by reducing the size in some other respect. If the span was altered, then changes in the induced drag might be expected. Flight-Lieut. Lucking said he thought the lecturer had not made out as good a case as he might have done for the all- metal seaplane. P'or instance, he related a case in which a large flying boat weighing some 18,000 lbs. when completed, gathered weight to the extent of 600 lbs. or so, a weight that could not be accounted for by the amount of bilge water. and which must therefore be ascribed to water soakage. The amount was a large proportion of the total weight, and if the all-metal flying boat avoided such soakage it was. he thought, one of the strongest arguments in favour of its adoption. With regard to the heavily loaded machine he said it might be expected that considerable difficulty would be experienced in taking off, unless the power-loading was very low. He would like to know whether the lecturer had found any trouble in getting the machine off. Col. Cave-Brown-Cave desired to know if the side-float arrangement adopted by Dr. Rohrbach gave good riding in a seaway. He also expressed some astonishment at the fact that, as far as had been possible to judge from the lantern slides, the hull was flat-bottomed. He would like Dr. Rohr bach to give the reasons which had caused him to adopt this hull form, assuming that this was the shape of the hull. Dr. Rohrbach in replying to the questions raised, said he agreed with Mr. Manning that the tapered wing was more economical in weight than the wing of rectangular plan form and without taper. It was, however, a question of expense. The tapered wing cost much more to build, at any rate so long as only small quantities were produced. If a type came to be produced in large quantities the tapering wing would, he thought, be adopted. On the question of corrosion, he had found that if care was taken to have the rivets made of the same alloy as that used in the sheet no trouble arose, while all seams and joints where two pieces of metal met should be electrically insulated from each other by some form of protective painting. As regards torsional strength of a wing, as a result of two years' experience, during which experiments had been made with portions of wings sand loaded and tested to destruction, it was now possible, by observing the direction and form of the fractures, to calculate the torsional strength and to strengthen the wing in the right place, lightening it in others, and thus provide the necessary strength without additional weight. In reply to Mr. North, the lecturer stated that the increase in wing loading was arrived at by a geometrical reduction in the size of the more heavily loaded machine. The two types were not of equal span, the one being of 20 m. span and the other of 29 m. span. The aspect ratio and other proportions remained unaltered. As regards the difficulty of getting oft with a heavily loaded machine, this was, Dr. Rohrbach stated, mainly a matter of designing the planing bottom of the hull so as to be in sym pathy with the higher wing loading. On the question of danger of the machine getting blown over by a lateral wind, the experiments were still being continued, but so far there had been no reason to fear that there would be any trouble on that score. The machine had been moored out in a high sea, and yet when tilted laterally to the extent of the dihedral angle (6 degrees) so that the one wing became horizontal, the wing tip had not touched even the crest of waves 4 ft. high. Col. Ogilvie expressed his agreement with the lecturer in the opinion that the question of the large machine could best be solved by adopting heavy wing loading. A very hearty vote of thanks was then passed, and an interesting evening came to a close. 0 IS E E COMMERCIAL AIRSHIP DESIGN* IT is useless to expect airship-owning firms to start running regular lines till they are convinced that the aeronautical engineers can provide them with airships that will attract passengers. Airships will not attract passengers till they are safe, and till the fares can bo low enough to bring them within the means of the average individual. Our commercial airship must fulfil the following requirements :— (1) It must be structurally strong. (2) It must be safe against fire. (3) It must be very controllable in any weather. (4) It must be cheap to run. Experience with earlier airships of the R 33 type and others has shown that ample strength can be obtained when half the total displacement is devoted to the hull and engines. The new commercial Zeppelin, Z.R. 3, has this proportion. With increase in size it is possible to allot a smaller proportion ate weight to the hull and engines while keeping the same strength. As to the type of airship—whether rigid or semi-rigid— for commercial purposes, it is too early to form a definite opinion. My personal preference lies with the semi-rigid, anyhow for the smaller sizes. The new Parseval type, for instance, consists of a keel the whole length of the ship supported by gas-bags, as in the Zeppelin type, but divided longitudinally as well as transversely. They are under steel nets, and over all goes an outer cover, leaving a six-inch space between it and the gas-bags all round, which is very suitable for filling with inert gas. The upkeep of such an airship should be simple and cheap, and the whole of the metal-work under compressive loads is easily kept under supervision, which is not the case in the rigid type. The advantages and disadvantages of the two types are so nicely balanced, that till a ship of each type, of similar size, and employed on the same service, has been tested over a long period, it will not be possible to reach a decision, but it may be accepted that both types are perfectly capable of running an airship service quite efficiently. Abstract of Paper read by Commander F. L. M. Boothby. C.B.E., ,™ tu„ i *.*.....•.._ -c A ._._ i.-..i cnrWioorc at tfie Engineers Club, before the Institution of Aeronautical Engineers, at oventry Street, W., on October 17 Safety against fire. The first and most pressing need is the abolition of petrol. There are always petrol fumes hanging about in large airships, and in hot climates the evaporation is serious. The most direct and simple way, of course, is to fit engines of the heavy- oil Beardmore type. A second way is to use hydrogen drawn from the gas-bags in conjunction with a heavy fuel in the ordinary engine, and the third way is to gasify crude oil, by a new process shortly to be introduced to the public by an inventor, a well-known petroleum expert. Before considering the merits of these three systems, we have to consider another point—namely, the protection of the hydrogen against fire by putting a layer of inert gas round it. Various methods have been suggested from time to time, such as double-walled gas-bags containing nitrogen or ammonia gas. Here we met the difficulty that when the airship rises the protective gas will expand and blow off into the atmosphere, and there is no means of replacing it. It has been proposed to insert ballonnets into each gas-bag, into which the inert gas would flow as it expanded, but in that case it would push out hydrogen and make the ship heavy. The double-walled gas-bags are also of undue weight. Bv far the simplest and most efficient means appears to be to utilise the exhaust gases for protective purposes. There is an ample and constant supply of these which have only to be cleaned and cooled below boiling point, so as not to hurt the fabric, and then turned into the ring space between the gas-bag and outer cover. The ordinary doped outer cover should be quite gas-tight enough to contain it. We need only deal with a portion of the exhaust gas, such as can be dealt with by the weight of apparatus we can afford to carry, and a large part of the cooling is done in the ring space. First we can use the gas for cooking, as at present, and then for warming the living spaces. If it requires further cooling it can be passed betwe en metal plates let in flush with the side in the slip stream of t he propeller and finally expanded into the ring space. Here, being heavier than air it will accumulate at the bottom, and the air will be forced out through lightly-loaded valves into the trunks for leading away hydrogen gas when valved, being' taken down to the bottom of the trunk below the hydrogen gas valve by a duct. When all the air is forced 687
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