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Aviation History
1913
1913 - 0396.PDF
1/llGHT Germans have only been paying the price of that experience which has given them a substantial lead over other countries where this type of aircraft is concerned. Germany has only been undergoing in the air what America and France and ourselves went through in the evolution of the submarine, except that in the latter case there was not so much said about the failures, and only the successes were made known, and then very meagrely. And, having paid the price demanded, with their eyes wide open, the Germans have done what they set out to do—to lead the world in dirigible construction. It is useless to blink apparent facts, and that this is the solid, cold-drawn truth admits of no argument. Now, what is the lesson that we have to learn and digest? Briefly and simply it is this, that if a Zeppelin airship can travel from Friedrichshafen to Luneville, it can equally accomplish the voyage from Cuxhaven to Sheerness, Harwich, or even Portsmouth or Devonport. It is beside the point to argue that " Z 4 " was a lame duck when she came to earth at Luneville. The cold fact is that she did arrive there, and that in getting there she had passed over certain of the French frontier fortresses, and that what has been done once can be done again and yet again. True, if the political relations between France and Germany were in such a state of tension that war was to be apprehended, the French air-fleet would have something to say in such a matter. The mere presence Of a German aircraft on the wrong side of the frontier would in all probability be taken as a legitimate casus belli—and the fortune of war would decide whether the Zeppelin accomplished its mission or not. That is why the PYench have an air-corps. They were the first to realise that attack from the air can only be efficiently and properly met in the air. But if British dockyards or towns were the objective instead of French fortresses, how much of the " fortune of war " would there be in it ? We have no air service like that of France to fend off an attack. Our diminutive dirigibles would be worse than useless, for their employment would simply mean the loss of lives that could ill be spared. Our aeroplane fleet, save the mark, might do something, but it is quite unknown yet whether or not the dirigible can be out fought by the aeroplane. So far, the idea is that it should in part be met by craft of its own char acter. Nothing but the actual shock of war can tell us definitely how things will work out. It is not of great use theorising in the absence of any kind of data. The safest, nay, the only course in the first instance, is to build dirigibles to fight dirigibles. That lesson seems slow to penetrate the minds of those in authority, which to us is more than a little strange. Supposing, for the sake of apt comparison, we, or any other reputable organ of public opinion, were to suggest to the Admiralty that the millions spent on building battleships for the express purpose of fighting battleships were absolutely wasted, and that if we spent half the money on small torpedo craft to fight the enemy's capital ships we should be quite safe, and save into the bargain. What would be said by naval experts? The answer is so self-evident that we need not trouble to set it down. And yet that is precisely what .we are doing in the air; or, to be more exact, we are talking about building a handful of aerial torpedo craft in readiness to fight battleships I Quos Deus vult perdere, prius dementat. APRIL 12, 1913. An interesting letter from a correspon- 3******"* dent in the current issue ought to be ° 1CS' read with appreciation by several of our other correspondents, who have been labouring with the problem of fair-shaped bodies mainly through the exercise of their imaginations. It is highly meritorious to use the imagination at all times, but it is also very desirable to feed it now and again on solid items of fact. Thus, in connection with fair-shaped bodies there is now a certain amount of information which it is impossible to disregard. Tests have been conducted at the National Physical Laboratory, and the results thereof have been published in the Technical Report of the Advisory Com mittee. In the last Technical Report are some photo graphs illustrating the fluid flow around various strut sections. Rough sketches which accompany our corre spondent's letter are substantially correct in giving a general idea of the result of three specific cases. They emphasise the turbulence in the wake of the obstruction, and they show how important is the tail portion of any fair-shaped body. In dealing with strut sections from a practical standpoint, it is, of course, primarily necessary to bear in mind that the main object of a strut is to be strong and also to be light. The question of weight, however, is also bound up with resistance, because if it is possible to save one pound in resistance it is possible, on most machines, to carry an extra six pounds weight by virtue of this saving. The reason for this is that most machines nowadays have a gliding angle that is at least one in six, which means to say that a pound resistance is as much of an obstruction to motion as six pounds weight in flight. It is assumed, of course, that the extra dead weight is hidden inside some obstruction that already exists, and does not add thereto the resistance of its own form. The problem of designing fair-shaped bodies for dirigibles is complicated by considerations of gas-carrying capacity in addition to strength and resistance, while in the case of a fair-shaped body for the purpose of enclosing the engine and the pilot on an aeroplane there is the fact that both objects to be enclosed already possess a certain size. In analysing the nature of the resistance of a fair- shaped body, there are two points of view that deserve consideration. One of them assumes that the resistance is of two parts, that due to friction and that due to form. The alternative line of thought regards the resistance as indivisible. Of the two arguments the latter, in so far as it affects long bodies, is, we think, best supported by experimental evidence. Those who favour the division of streamline resistance into friction and form are faced with the necessity of supposing that the whole of the frictional resistance is given by Zahm's formula and coefficient. The remainder is thus arbitrarily assigned to the projected area of the cross-section, and, therefore, is assumed to conform to the V2 law as being related to the pressure on a flat plate. Zahm's formula, as corrected by the N.P.L., is F lbs. = -0000082 A0-93 zA'86, while the face pressure formula for a flat plate is F lbs. = ^ Aw*. 400 In the above expressions the term A in the first case relates to the exposed surface, and in the second place to the area of the projected cross-section. Assuming that the frictional formula is to be applied as it stands without altering the numerical value of the 402
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