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Aviation History
1913
1913 - 1308.PDF
this paper, but I would urge that when discussing it we should have fair play as between the two types. Lines of Development Here and Abroad.—The develop ment of the airship in England and on the Continent has proceeded on different lines, due, I fancy, largely to the differences in the nature of the countries and of national temperament. Here, we have set rather the maximum power of control and handiness as our aim ; abroad, they have gone in for weight-carrying capacity and long distance work. In consequence the foreign airships appear clumsy to our eyes and difficult to manage ; while ours, no doubt, appear to them as puny and contemptible. When the Parseval airship, which now belongs to the Navy, descended after its first flight in this country, I asked the German pilot what he thought of our country from the air. He remarked at once that it was so very full of trees, and added that he did not con sider it a good country for airships. He was right and yet wrong : right from his own point of view and wrong from ours. It is un deniably not a good country for German airships such as the Parseval and others, but it is excellent for the type that has been developed in England. Now, please do not misunderstand me in this connection—I do not now refer to the relative sizes of the airships, but to their methods of control. In Germany or France an airship pilot selects a wide open space to land in ; in England we look for a field completely surrounded by trees and just big enough to take the airship. On manoeuvres last September we had two airships, " Delta" and " Eta," and these were moored out in the open behind a row of trees about 55 ft. high, such in fact as one finds all over England. " Delta " stands 65 ft. high, that is to say, quite markedly more than a Zeppelin or other rigid ship, and yet throughout the week it was in the open, whether the wind was 50 m.p.h. or whether it was a calm ; the ship's crew of six or eight were ample to look after it, except when landing. This compares favourably with the 200 or more required to hold a Zeppelin in the open. And I maintain that a rigid ship of the largest size could have been managed in the same way by a score or so of men, though possibly, and perhaps I should say probably, not of the Zeppelin type of construction. Both our two ships were out in much rain and other bad weather. Speed.—A year or two ago Major Baden-Powell informed the world, through the Daily Telegraph, that non-rigid ships could not hope to greatly exceed 35 miles per hour, because the flexible envelope would not stand it. To-day the " Astra Torres " airship, or as it now is, Naval Airship No. 3, has achieved a speed, independently of the wind, of over 51 miles per hour. It is there fore the fastest non-rigid airship in the world and may well be even better than the Zeppelins, but precise information on this point is lacking. Competent designers assure us that 55 miles per hour can be easily obtained and another year or so may produce the 60 miles per hour airship. From the war point of view this increase in speed has a most important corollary; it means that the era of the slow-speed aeroplane, that is to say, those of under 60 miles per hour, will be gone for ever. Everything that they can do can be done so much better by the airship. If ever airships achieve 70 miles per hour it is difficult to see where the aeroplane, as we know it to-day, will come in at all for war purposes; and this, of course, applies equally to seaplanes. This is no idle boast, but the natural result of increase of speed. Safety,—We have all been appalled by the recent disasters in Germany. We can only surmise what happened in each case and must on no account, therefore, jump to conclusions too hastily. As I said before, the statement in the Standard that the Zeppelin is proved a failure and should be abandoned, seems to me particularly foolish and unfortunate. We are very badly served by our Press in aeronautical matters ; so-called experts do not hesitate to write down amazing rubbish, and editors print it gladly ; the general public accept it as gospel, and so the trend of public opinion is induced into wrong lines and the cause of aeronautics suffers. But to return to the question of safety. In any airshipySVr is above all the greatest danger. If you will bear with me I would like to analyse this question a bit. There are three main sources of fire :— (1) From the engines. (2) From the " wireless " apparatus. (3) From other sources, such as defective wiring in the electric lighting circuit, matches, and so on. There are also three sets of combustible material which may be set alight :— (1) The gas within the envelope. (2) The petrol for the motors. (3) Such portions of the car and framework as are not made of metal. Of the sources of fire :— (1) At the engine a great deal can be done to render the risk small, but it cannot be entirely eliminated. The carburettor can be and should be enclosed in wire gauze, and the red-hot portions of the exhaust pipes should be dealt with in the same way. Large and ample silencers are valuable because not only do they quiet the engines, but they cool down the exhaust gases. . (2) All dangers from "wireless" sparks can be eliminated by suitable design, but the apparatus wants most careful working as accidental damage to the insulation is almost certain to cause a spark. (3) Risks from other sources are small and can be easily provided for. Then as to combustible materials. We have to use hydrogen in the envelope, and there must be occasions when that hydrogen must escape. An entirely satisfactory automatic valve which can be placed on top of the envelope has yet to be devised. In semi- and non-rigid airships the automatic gas valves: are placed at the extreme stern. In rigid ships they cannot be placed there, and there is some ground for believing that the importance of this point has been overlooked. It is possible, though I must confess I think it is very unlikely, that a sufficiently light gas can be found which, when mixed with hydrogen, will render it non-inflammable, and yet not materially impair its lift. It is certainly a point to which chemists should turn their attention. Petrol we have to carry ; we may use heavy oils one day— certainly not for some time. It is scarcely necessary to say that petrol is harmless while enclosed in its tanks, especially if they are far removed from any source of fire. We have therefore two opposing requirements:—For maintaining balance it is necessary to keep the tanks amidships, and as a fire precaution to keep them away from the engines. One solution would be to keep them inside the envelope, but this adds a variety of other difficulties in connection with refilling, leakage, and so on. If petrol is carried near the engines, it should be aft them so that petrol vapour, due to leakage, is carried away, by the natural draught, out of danger. It is undoubtedly better if all fabric and other combustible material be kept away from the car ; but this involves an increase of weight which cannot be faced in small ships, and we have then to resort to fire-proofing and similar palliatives. Of risks other than that from fire, I look upon the possibility of a propeller blade breaking and flying into the envelope as the worst. This danger is comparatively small in a Zeppelin, because the gas is confined in 17 different compartments and only one can be rent by a propeller breaking. In a non-rigid ship such an accident will be fatal and involve the complete destruction of the ship unless the envelope is provided with a proper system of internal partitions. Partitions are also needed for other reasons, as I will show below. This is no small risk, as such things as a cap, a nut, or other article getting into the revolving propeller is practically certain to cause the blades to break and fly. Guards are not practicable for the large propellers now in use, and in any case their weight and head resistance render them out of the question. There are, of course, other risks in airship work, but they are of lesser importance and need not be considered in estimating the safety of airships. Design Details.—To turn now to matters of detail in design. Envelopes.—The envelope is usually made of a fabric of cotton and rubber and is dyed yellow. In England we have also tried varnished silk and gold-beater's skin. Silk was not a success ; difficulty was experienced in making the seams strong enough. Gold-beater's skin is excellent in many ways ; it lasts in the most wonderful manner without deterioration, holds gas well, and can be easily repaired. But in wet weather it absorbs a great deal of moisture and takes an appreciable time to dry. The materials of which it is made are difficult to obtain quickly, and the process of manufacture is rather slow. Cotton and rubber fabric has been hitherto the stand-by of all airship manufacturers. It is, however, heavy compared with silk, and succumbs very quickly to the effects of rain and sun. It absorbs a fair amount of moisture in wet weather, but not so much as gold-beater's skin. It is easy to repair and can be manufactured with ease by machinery. A new material has now been discovered, and it is hoped that with this we shall have the following advantages :—-Firstly, it is easily made; secondly, it will hold gas well ; thirdly, it will not deteriorate ; fourthly, it will absorb no moisture. So far these advantages have been borne out in practice, but further trials will be necessary before we can say quite positively. 1334
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