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Aviation History
1914
1914 - 0420.PDF
I/ED two layers of air travel smoothl , with only the smallest area of disturbance between the two layers ; and when it is remembered that there are thousands of square miles over England alone of contact surface between the two layers, one must at once realise that the friction between the two layers must be infinitesimal in order to preserve their distinct directions. I now come to the third point—namely, why the wind should fall calm on the ground whilst remaining in swift motion above. It is obvious that wind travelling in contact with the ground must meet with considerable resistance. This is proved by the comparatively slow travel of air when measured close to the ground, and its increase in speed at higher altitudes. Consequently, the air under the influence of friction drag caused by proximity to the earth's surface, tends to arrest the progress of the air above, and if the tenacity of the large bulk of air be sufficient to move the ground layer, the latter travels with it ; if it be insufficient, then the air splits, leaving the lower portion stagnant, and the upper portion travelling at the original pace. This would explain why they separate, but it does not explain why they join again when the sun rises. I assume that a constant mixing or interchange between the travelling atmosphere and the ground layer is necessary in order that the ground layer may be moved under the influence of the upper layer. At night there is nothing to cause disturbance in calm air on the ground, but when the sun comes out in the morning, objects on the ground become slightly heated, and cause bubbles of air to rise from the stagnant portion below into the portion which is moving above. A bubble of warmed air rising soon becomes a twisting column, and when you think that the proportion of thickness between the two layers of air may be likened to two table-cloths spread over a table, it will be readily realised that when some thousands or millions of these columns or bubbles are rising from one layer to the other layer, and similar quantities of cooler air are descending to take the place of the rising air, then the effect is similar to the effect of the upper table cloth becoming pinned to the stationary under table-cloth, with the result that the two layers again move along together. In order to show that I have not digressed too far away from my subject, I will endeavour to illustrate how an understanding of these wind conditions might have saved the lives of perhaps more than one flyer. Imagine an aeroplane coming down from a great height, head on to a wind blowing twenty miles an hour. On arriving, say, loo ft. from the ground, the machine runs suddenly into the stagnant ground layer of air, and the flying speed through the air is immediately reduced by twenty miles per hour. The machine naturally stalls and dives, and the altitude being insufficient to recover control, the machine strikes the ground before control can be recovered. Many accidents have occurred owing to the diving of machines just prior to landing when perhaps loo ft. in the air, and I cannot help thinking that wider knowledge gained in balloon ing may add to the understanding of the air, and thus increase the safety of pilots when flying and prove beneficial in their training. Lieutenant Fletcher's Paper. Mr. Griffith Brewer has raised a large number of interesting questions in his share of this lecture, and has covered the ground very completely. It is left to me to remark on special features of the subject in their application to military aviation, and perhaps to amplify somewhat further some of the original problems. The Pioneer Work of Ballooning.—It will probably never be recognised how much the science of aviation owes to ballooning. Ballooning at the present day is in danger of sinking into complete obscurity, at least in this country, and I think also in France. Its use becomes less apparent every day, and I am very glad to have the opportunity to plead for it, though I cannot but regret that you should have been robbed of the pleasure of hearing Major Maitland speak on a subject on which his experience gives him the first claim to address you to-night. He has, however, very kindly allowed me to draw on his experiences and ideas. Ballooning must be given credit for the work it has done in the past. Many of the most elemental y bits of knowledge stored away in the experience of aeroplanists of to-day owe their entire con ception to ballooning. The whole branch of lighter-than-air flying owes its being to ballooning. And the grcund has not yet all been broken. There is a great deal of work to be done ; and many lines of study are daily opened to balloonists, and can, indeed, only be carried out by balloonists. The subject falls into two headings, viz., the value of ballooning as a preparation for flying and the value as actual training. I wish to make it clear that the first heading is a fair sub-division of the lecture. It is to my mind of the utmost importance from a Service point of view. Experience of the air we fly in is necessary. Accurate knowledge cannot be gained from mobile aircraft; it is our object to show that it may, in part, at any rate, be gained from a proper development of the science of ballooning. Wind Charts.—How many aeroplanists are aware of the APRIL 18, 1914. interesting phenomenon mentioned by Mr. Brewer that the wind direction varies at different altitudes ? And of those who know that the wind's direction alters how many have tried to make use of their knowledge ? On July 13th, 1912, a long-distance balloon raca was held. The day was hot and thundery and the ground wind fickle. Pilot balloons sent up berore the race drifted eastwards down the Thames. Those who watched the clouds saw the lower ones travelling South, but the mackerel sky above travelling North. Seven balloons went up from Hurlingham, of which four went South to Brighton at an average height of not more than 5,000 feet. The other three, choosing various altitudes, according to their ballast capacities, made Sauthampton, Bith and Market Harborough respectively. The last-named must have travelled at an average height of 12,000 feet. The billoon I was in described a very marked " S,'' the northerly inclined limb, from south oi Godalming to Fleet, being at 10,000 feet. An aeroplane flying on that day from London to Vork, 200 miles approximately, could, by flying at 10,000 ft. instead of 3,000, have saved about two hours on the journey. The two opposing currents were, I should siy, about 20 m.p.h. at each level. The condition can be predicted by meteorologists, and it is of no small importance to aeroplanes to know and make use of it. Their endurance is limited to say five or six hours at war load. If, then, they can fiud favourable currents in all directions, they can save much petrol and oil, and add a considerable percentage (in the case we have con sidered about 50 per cent.) to the number of miles they can travel in the air. On the chance of effecting such a saving it is worth while to climb to various heights and observe progress over the ground at those heights. This can now be done very easily by means of a little camera-obscura apparatus, in which the time taken for the image of a ground object to pass between two lines can be read off directly (as a function of the height) as speed over the ground. It might well be remarked here to those who object that too much is being demanded from the aeroplane pilot, that war is a scientific game, and must be waged scientifically. If by application of scientific methods we can increase the aeroplane's radius of action ever so little, then those methods are worth adopting ; and the pilot must be trained accordingly. Sea breezes.—Sea breezes provide another important field of research for balloonists. On one occasion Major Maitland left London in his balloon in a flat calm. After hanging motionless for an hour or so he decided to go up higher, and went to 9,000 ft. through the clouds. There he remained i^ hours out of sight of land. I have his permission to point the moral which follows. For he then heard the hoot of a steamer, and on coming down to investigate, found the Newhaven boat just arriving, as it were, at his feet. Moral : Do not remain in balloons for more than half-an- hour anywhere in England out of sight of the ground. This is made an order for military balloons, and should never be forgotten by anyone. A record descent was made, but at about 800 ft. a strong sea breeze was met, which carried him Londonwards at 25 m.p.h. Unfortunately, lack of ballast prevented him from saving railway fares to any appreciable extent, and he had to land. It would have been interesting to know where and why that breeze would have failed. Many countries in this world have nothing but sea and land breezes for six months in the year. Use could be made of them in much the same way that the barge and the steamer alike use tides to help them up and down the Thames, The e matters can only be properly investigated by balloonists, for, as Mr. Brewer points out, you cannot investigate wind strengths and directions from the deck of an ocean liner. Suggested Scientific Organisation of Ballooning.—I should like here to plead tor some kind of organisation among balloonists in this country. A few individuals make weekly ascents from London. They store up for themselves a vast deal of experience and weather wisdom, but little of this gets any further. On the other hand, most Germnn aeronautical papers give a page or two to ballooning, A sym psis of balloon ascents for the month chronicles always some v two or three hundred agents. Another page is given to the more interesting ascents ; and altogether, it is clear that an organisation exists to provide a common fund of experience from which all can diaw. I would go further. I would suggest that the Meteorological Office amplify its wind chart system, and publish daily information of the upper currents, so far as they can be ascertained or predicted, and that ultimately a probability chart be got out showing upper wind directions and forces for all systems of weather. These charts would be liable to daily revision by telegraph, but they would be a great guide to pilots flying high. It is a formidable task. But if more people ballooned from more centres, and if they sent in their reports to a central registry, and if they would as>ist in the pilot balhon ascents made under the auspices of the I.M.A., we should, in five \eais, have an invaluable fund of knowledge. Night flying, fog flying, flying above clouds, would be as safe and certain as 420
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