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EXPERIMENTS WITH DIRIGIBLE

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Originally appearing in Volume V01, Page 270 of the 1911 Encyclopedia Britannica.
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EXPERIMENTS WITH DIRIGIBLE BALLOONS Giffard, the future inventor of the injector, devised a steam-engine weighing, with fuel and water for one hour, 154 lb per horse-power, and was bold enough to employ it in proximity to a balloon inflated with coal gas. He was not able to stem a medium wind, but attained some deviation. He repeated the experiment in 1855 with a more elongated spindle, which proved unstable and dangerous. During the siege of Paris the French government decided to build a navigable balloon, and entrusted the work to the chief naval constructor, Dupuy de Lome. He went into the subject very carefully, made estimates of all the strains, resistances and speeds, and tested the balloon in 1872. Deviations of 12° were obtained from the course of a wind blowing 27 to 37 M. per hour. The screw propeller was driven by eight labourers, a steam-engine being deemed too dangerous; but it was estimated that had one been used, weighing as much as the men, the speed would have been doubled. Tissandier and his brother applied an electric motor, lighter than any previously built, to a spindle-shaped balloon, and wenf up twice in 1883 and 1884. On the latter occasion he stemmed a wind of 7 M. per hour. The brothers abandoned these experiments, which had been carried on at their own expense, when the French War Department took up the problem. Renard and Krebs, the officers in charge of the War Aeronautical Department at Meudon, built and experimented with in 1884 and 1885 the fusi-form balloon " La France," in which the " master " or maximum section was about one-quarter of the distance from the stem. The propelling screw was at the front of the car and driven by an electric motor of unprecedented lightness. Seven ascents were made on very calm days, a maximum speed of 14 M. an hour was obtained, and the balloon returned to its starting-point on five of the seven occasions. Subsequently another balloon was constructed, said to be capable of a speed of 22 to 28 m. per hour, with a different motor. After many years of experiment Dr Wolfert built and experimented with in Berlin, in 1897, a cigar-shaped balloon driven by a gasoline motor. An explosion took place in the air, the balloon fell and Dr Wolfert and his assistant were killed. It was also in 1897 that an aluminium balloon was built from the designs of D. Schwarz and tested in Berlin. It was driven by a Daimler benzine motor, and attained a greater speed than " La France "; but a driving belt slipped, and in coming down the balloon was injured beyond repair. From 2897 onwards Count Ferdinand von Zeppelin, of the German army, was engaged in constructing an immense balloon, truly an airship, of most careful and most intelligent design, to carry five men. It consisted of an aluminium framework containing sixteen gas bags with a total capacity of nearly 400,000 cub. ft., and it had two cars, each containing a 16 h.p. motor. It was first tested in June 1900, when it attained a speed of 18 m. an hour and travelled a distance of 31 M. before an accident to the steering gear necessitated the discontinuance of the experiment. In 1905 Zeppelin built a second airship which had a slightly smaller capacity but much greater power, its two motors each developing 85 h.p. This, after making some successful trips, was wrecked in a violent gale, and was succeeded by a third airship, which, at its trial in October 2906, travelled round Lake Constance and showed itself able to execute numerous curves and traverses. At a second series of trials in September 1907, after some alterations had been effected, it attained a speed of 36 m. an hour, remaining in the air for many hours and carrying nine or eleven passengers. A fourth vessel of similar design, but with more powerful motors, was tried in 2908, and succeeded in travelling 250 M. in 11 hours, but owing to a storm it was wrecked when on land and burnt at Echterdingen on the 5th of August. Subscriptions, headed by the emperor, were at once raised to enable Zeppelin to build another. Meanwhile in 1901 Alberto Santos Dumont had begun experiments with dirigible balloons in Paris, and on the 19th of October won the Deutsch prize by steering a balloon from St Cloud round the Eiffel tower and back in half an hour, encountering on his return journey a wind of nearly 5 metres a second. An airship constructed by Pierre and Paul Lebaudy in 1904 also made a number of successful trials in the vicinity of Paris; with a motor of 40 h.p., its speed was about 25 M. an hour, and it regularly carried three passengers. In October 1907 the " Nulli Secundus," an airship constructed for the British War Office, sailed from Farnborough round St Paul's Cathedral, London, to the Crystal Palace, Sydenham, a distance of about 50 m., in 3 hours 35 minutes. The weight carried, including two occupants, was 3400 lb, and the maximum speed was 24 M. an hour, with a following wind of 8 m. an hour. Thus the principles which govern the design of the dirigible balloon may be said to have been evolved. As the lifting power grows as the cube of the dimensions, and the resistance approximately as the square, the advantage lies with the larger sizes of balloons, as of ocean steamers, up to the limits within which they may be found practicable. Count Zeppelin gained an ad-vantage by attaching his propellers to the balloon, instead of to the car as heretofore; but this requires a rigid framework and a great increase of weight. Le Compagnon endeavoured, in 1892, Dirigible balloons. Dia- Con- Lifting Weight Weight Speed Year. Inventor. Length. meter. Capa- of of H.P. per tents. city. Balloon. Motor. hour. Ft. Ft. Cub. ft. lb. lb. lb. Miles. 1852 Giffard d . . 144 39 88,300 3,978 2,794 462 3.0 6.71 7 Dupuy de Lome . . . 118 49 120,088 8,358 4,728 2000 o•8 6.26 1884 Tissandier 92 30 37,439 2,728' 933 616 1.5 7.82 1885 Renard and Krebs . . 165 27 65,836 4,402 2,449 174 9.0 14.00 1897 Schwarz . . 157 ) 346 9 130,500 8,133 6,800 Soo? 16•o 17.00 1900 Zeppelin I. 420 39 400,000 25,000 19,000 1500 32.0 18.00 1901 Santos Du- mont VI. 108 20 22,200 .. .. .. 16.20 19.00 1908 " Republique " 195 35 130,000 3,100 .. .. 8o 3o 1908 Zeppelin IV. . 446 421 450,000 .. .. .. 220 270 to substitute flapping wings for rotary propellers, as the former can be suspended near the centre of resistance. C. Danilewsky followed him in 1898 and 1899, but without remarkable results. Dupuy de Lome was the first to estimate in detail the resistances to balloon propulsion, but experiment showed that in the aggregate they were greater than he calculated. Renard and Krebs also found that their computed resistances were largely exceeded, and after revising the results they gave the formula R=o•o1685 D2V2, R being the resistance in kilograms, D the diameter in metres and V the velocity in metres per second. Reduced to British measures, in pounds, feet and miles per hour, R= o•0006876 D2V2, which is somewhat in excess of the formula computed by Dr William Pole from Dupuy de Lome's experiments. The above coefficient applies only to the shape and rigging of the balloon " La France,” and combines all resistances into one equivalent, which is equal to that of a flat plane 18/0 of the " master section.” This coefficient may perhaps hereafter be reduced by one-half through a better form of hull and car, more like a fish than a spindle, by diminished sections of suspension lines and net, and by placing the propeller at the centre of resistance. To compute the results to be expected from new projects, it will be preferable to estimate the resistances in detail. The following table shows how this was done by Dupuy de Lome, and the probable corrections which should have been made by him: RESISTANCES—DUPUY DE LOME'S BALLOON Computed by Dupuy de Lome. MoreProbableValues. V = 2.22 in. per sec. V = 2.82 m. per sec. Part. Area, Co- Air Resist- Co- Air Resist- Sq. effici- Pres- ance, effici- Pres- ance, Metres. ent. sure. Kg. ent. sure. Kg. Hull, with- 172.96 ,/3o 0.665 3.830 1/15 0.875 IO.091 out net. . Car 3.25 1/5 ,, 0.432 1/5 ,, 0.569 Men's bodies 3.00 1/5 „ 0.400 1/2 „ 1.312 Gas tubes . 6.4o 1/5 „ 0.850 1/2 „ 2.750 Small cords Io•oo 1/2 3.325 1/2 ,, 4.375 Large cords 9.90 1/3 2.194 1/3 „ 2.887 11.031 .2P984 When the resistances have been reduced to the lowest possible minimum by careful design, the attainable speed must depend upon the efficiency of the propeller and the relative lightness of the motor. The commercial uses of dirigible balloons, however, will be small, as they must remain housed when the wind aloft is brisk. The sizes will be great and costly, the loads small, and the craft frail and short-lived, yet dirigible balloons constitute the obvious type for governments to evolve, until they are superseded by efficient flying machines. (See further, as to the latter, the article FLIGHT AND FLYING.) The chief danger attending ballooning lies in the descent; for if a strong wind be blowing, the grapnel will sometimes trail for miles over the ground at the rate of ten or twenty miles Practice an hour, catching now and then in hedges, ditches, roots t aero- s tation. tion. of trees, &c.; ; and, after giving the balloon a terrible s jerk, breaking loose again, till at length some obstruction, such as the wooded bank of a stream, affords a firm hold. This danger, however, has been much reduced by the use of the " ripping-cord,” which enables a panel to be ripped open and the balloon to be completely deflated in a few seconds, just as it is reaching the earth. But even a very rough descent is usually not productive of any very serious consequences; as, although the occupants of the car generally receive many bruises and are perhaps cut by the ropes, it rarely happens' that anything worse occurs. On a day when the wind is light (supposing that there is no want of ballast) nothing can be easier than the descent, and the aeronaut can decide several miles off on the field in which he will alight. It is very important to have a good supply of ballast, so as to be able to check the rapidity of the descent, as in passing downwards through a wet cloud the weight of the balloon is enormously increased by the water deposited on it; and if there is no ballast to throw out in compensation, thevelocity is sometimes very great. It is also convenient, if the district upon which the balloon is descending appear unsuitable for landing, to be able to rise again. The ballast consists of fine baked sand, which becomes so scattered as to be inappreciable before it has fallen far below the balloon. It is taken up in bags containing about i cwt. each. The balloon at starting is liberated by a spring catch which the aeronaut releases, and the ballast should be so adjusted that there is nearly equilibrium before leaving, else the rapidity of ascent is too great, and has to be checked by parting with gas. It is almost impossible to liberate the balloon in such a way as to avoid giving it a rotary motion about a vertical axis, which continues during the whole time it is in the air. This rotation makes it difficult for those in the car to discover in what direction they are moving; and it is only by looking down along the rope to which the grapnel is suspended that the motion of the balloon over the country below can be traced. The upward and downward motion at any instant is at once known by merely dropping over the side of the car a small piece of paper: if the paper ascends or remains on the same level or stationary, the balloon is descending; while, if it descends, the balloon is ascending. This test is exceedingly delicate.
End of Article: EXPERIMENTS WITH DIRIGIBLE
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