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Aviation History
1913
1913 - 1175.PDF
NOVEMBER I, 1913. Lines of force influence the aircraft that has become an electro scope. For this reason one can determine more or less exactly at at certain moments of the day, that when flying above a known spot an aircraft is subjected to a finite movement. Not knowing to what to attribute these harsh movements, which the control is unable to counteract, they have been called by the general terms " heat remous," " air-holes," &c. They are very dangerous and very rough. One wing alone sometimes enters the region of disturbance, and is suddenly arrested in a way that swings round the machine. Often the whole aircraft is suddenly drawn down or thrown upwards, without those on board following the same movement. These are the lines of force due to the nature of the soil and sub-soil, which under the influence of the solar rays pass through maxima and minima, acting on the flying electroscope. Since for the moment we cannot change the intensity or direction of the lines of force, we must try and render the aircraft as slightly sensitive as an electroscope as possible. What changes its sensitive ness is its surface electric potential, so we we must look first of all for the means of producing the least electricity possible, and secondly for means for neutralising its effect, or for facilitating its rapid dissipation into the surrounding medium. Let us take, for example, the Bristol monoplane, which I know in every detail. I need 49 h.p. to fly horizontally at 120 k.p.h., with a weight (of machine only) of 830 kilos. For support and driving power proper, eliminating friction, we use 42 h.p. Thus, 7 h.p. are absorbed by friction. In measuring the heat generated by the friction, we see that it corresponds to no more than a fifth part of the calories, equivalent to 7 h.p. It remains, therefore, to ascertain in what form the other four-fifths of the 7 h.p. manifests itself. The varnish on the wings has a cellulose base. If we rub lightly, and at a moderate temperature, on this varnished surface, we find that the varnished surface quickly adheres to the hand. This electricity is dissipated, however, after an interval under an ionising action. If the surface is varnished with a material having an acetate of cellulose as a base, and is coated on the surface with a varnish made according to the directions of E. Castelaz and Depoully, in a patent of 1879, we shall find a tendency towards a more rapid dissipation of the electricity into the surrounding air. This tendency is again augmented by the procedure of Wachendorff, described in a patent of 1905. Wachendorff mixes in his varnish a hydro-oxide or a basic silica of aluminium. The latter procedure facilitates such rapid discharge of the electricity that it is difficult to exactly measure the quantity produced by the friction. The colour of the varnish has a great importance under the influence of the ionising rays. The best colour for varnishes of a cellulose base is blue-black or brown-black. In measuring the work done on overcoming air friction on a moving surface, we arrive at results similar to those of Zahm and Franck. Their formulas, however, cannot give a perfect relationship, since they neglect the exterior of the surface. I, therefore, made the following experiment:— The conduct of these tests is a delicate matter, on account of the very feeble forces to be observed and the complications that inter vene. In a bell-jar I produced the best vacuum that I could obtain. Therein I placed a very thin flywheel, which was rotated by an electric motor. By this means I measured the friction of the bearings. Then I admitted air, and measured the power absorbed at different speeds, from whioh figures I subtracted the correspond ing losses in the bearings, and so determined the work done on air ® ® An Aeroplane Rally at Monte Carlo. ONE of the most ambitious schemes which has yet been put forward by responsible people in connection with the aeroplane is nothing less than an International Rally on somewhat similar lines to the meetings for motor cars which have proved so popular on the Continent. The organisation is by the Sporting Club of Monaco, and it is proposed to have the rally at Monte Carlo during the first fortnight of next April. Seven routes have been provisionally selected, each of approximately the same length :— 1. London-Calais-Dijon-Toulon-Monte Carlo. 2. Brussels-Calais, and then as No. I. 3. Paris-Angers-Toulouse-Toulon-Monte Carlo. 4. Gotha-Frankfort-Dijon-Toulon-Monte Carlo. 5. Madrid-Bilbao-Toulouse-Toulon-Monte Carlo. 6. Vienna-Agram-Venice-Genoa-Monte Carlo. 7. Rome-Turin-Venice-Genoa-Monte Carlo. The entrants will be free to start from March 31st to April 14th, and they must arrive at Monte-Carlo not later than April 15th. The prizes amount to ^3,000, and will be divided as follows : To the pilot making best time over any itinerary ^1,000, the best time by a machine of over 25 square metres surface, ^400, the second best time over any itinerary ,£200. The best time over each route will secure for the pilot .£200. riction. I then enlarged the flywheel so as to increase the peripheral surface, for which I could ascertain the exact speed. Again I made a vacuum in the bell-jar, and again introduced air as before. In this way I ascertained that the friction within wide limits is proportional to the air pressure on the surface and to the square of the speed. I changed the hygrometric state of the air for a given pressure, and found very slight variation in the power. In enlarging the surface I noticed that the friction was not directly proportional thereto, but that it was proportional to the total pressure exerted on the surface. Finally, I insulated the surface from the rest of the flywheel, and was thus able to measure the static electricity produced. The charge rapidly attained a maxima, and stayed there. This maxima varied within wide limits with the quality of the surface. The temperature variation around the flywheel, or on the flywheel itself, is very difficult to measure. From these experiments I found that the greater part of the power expended on friction went into the production of surface electric potential, which establish a state of equilibrium by contact with the surrounding medium. If we take a wooden surface that is highly polished, and is under a pressure of 760 mm., we can prove the formula of Franck to be correct. This formula gives : F = 0'365 kg. /meter- for a speed of which the second power is i.oco. So long while the maximum value observed on the ordinary varnish is very high, the results for metallic varnishes reach very low maxima—that is to say, they facilitate the rapid discharge of the surface electricity into the surrounding medium. In order to complete these tests I tried, but without much success, to make some out of door experiments with large kites. Also I tried model kites in a wind tunnel to obtain the pull on the wire for varying wind speeds. Experimenting afterwards on a much larger scale, I hoped to determine the speed of the wind by the pull on the wire (taking account, of course, of the weight of the wire). The results were unsatisfactory, and I do not think the means employed were of the best. However, I was able to ascertain in a very high wind by covering the cable with a small copper wire to make it a good conductor, the anchorage of the cable being insulated from the earth, that the electrical state varies very little while the sky is free from clouds. These changes become very irregular when the sky is overcast, and when clouds cross the sun so that the kite flies either in full sunlight or in shade. The variations did not correspond at all to the changes in the pull on the cable, which was produced by a fluctuating wind. I do not, however, care to deduce anything from those experiments which, although interesting, were not very perfect. From my experiments I conclude that an aircraft is an electroscope, the more sensitive if it flies fast, its sensitiveness being proportional to the square of the speed. The sensitiveness is also related to the weight of the machine on account of the connection between pressure and weight. The size of the surface itself is of no consequence. Then, to be able to fly in daylight under the electro-optical reactions between the solar rays and the earth over which the machine is flying, it is necessary that the aircraft should fly slowly and should be light, and that its colour should facilitate the rapid discharge of surface electricity generated during flight by the friction of the wings. Further to facilitate the discharge it would be useful to turn towards the rear of the machine such members as may conveniently be made pointed in shape. ® ® AIRSHIP MEWS. The New Veeh Dirigible on Trial. THE new Veeh dirigible was out for a trial on Saturday last, and after a short voyage along the Rhine valley with thirteen persons on board, returned to her shed at Dusseldorf. When she came to landing, however, the airship refused to answer the helm, and as the wind threatened to drive the vessel against her shed, there was considerable anxiety for some few minutes. Eventually the airship was got under control, but not before three soldiers had been injured. The Causes of the Zeppelin Disaster. A REPORT by Dr. Eckener on the catastrophe to the German naval Zeppelin L2 attributes the disaster to :— 1. The passage-way connecting the gondolas having been placed inside the carcase. 2. The gondolas having been brought nearer to the envelope. 3. The placing of a wind screen at the front of the leading gondola, which contained two motors. The report indicates that it was the wind screen which was really the primary cause of the disaster, as owing to its suction effect it caused the gas escaping from the ballonets when the airship rose, to collect in the gondola where it was ignited by a spark from the motor. 1201
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