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Aviation History
1925
1925 - 0203.PDF
APRIL 2, 1925 —that is, 30 per cent, of the total lift—and a speed of only 18 m.s., then you will realise the tremendous headway recorded in the meantime." Dr. Eckener referred to the change in fineness ratio incor- porated in the " Bodensee," which was considerably more plump than the older airships, and he said that the small ratio of length to diameter chosen was only decided upon after wind-tunnel tests had shown that such a proportion could be stabilised without too large tail surfaces. He stated, however, that their experience with the " Bodensee " led them to the conclusion that it was not advisable to reduce the proportion of length to diameter too much, especially with larger ships. Consequently, somewhat less extreme propor- tions were chosen in building the Z.R.III. Some interesting particulars were then given relating to the wind channel used by the Zeppelin Company at Friedrichshaven. This measures 2-9 m. (9 ft. 6 ins.) in diameter, and wind speeds up to 50 m. per second (111J m.p.h.) can be attained. In spite of the great value of this wind tunnel, the lecturer expressed the opinion that a complete transference of the channel results to the full-size airship would scarcely ever be possible without a great number of measurements and experiments with the airship in action. Concerning the Z.R.III Dr. Eckener said :— " The decree of the Ambassadors' Conference had fixed the cubic capacity at 70,000 cub. m. The length of the ship is 200 m., the proportion of diameter to length is about 1:7-3; it is somewhat more slender than the ' Bodensee,' but not quite as slender as the 56,000 cub. m. type used during the War. It has an outright streamline shape, without cylindrical centre-piece. The course stability of the ship is a very good one, particularly as a result of the excellent efficacy of the fins. Trials in the wind channel had shown that the fins are most efficacious when they arc placed at a certain distance from the stern, and our experiences with Z.R.III confirmed this As a consequence the size of the fins could be reduced, which, together with their more favourable location, with regard to the strain on the ship, is equally advantageous, probably particularly so for ships fastened to a mooring mast. " As for the details of the Z.R.III, I shall confine myself to a few characteristic facts, since the ship as a whole is, no doubt, pretty well known to all those interested. The Z.R.III shows a novel construction of the corridor, which deviates somewhat from the circle of the cross-section of the ship's body without, however, thereby reverting to the type of outer corridor, in contrast to the inner one used during the last few years. " Furthermore, the ship was equipped with a new type of engines, namely, 400 h.p. Maybach motors, which have ball bearings instead of the former bearings, and which can be started and reversed by compressed air. "The speed of the Z.R.III is 35-3 m.s., its carrying capacity 46,000 kgs.—that is, 56 per cent, of the total lift. Although the ship does not in point of size, speed, and lift exceed the last War-time types of airship to a considerable degree, it still represents an appreciable measure of progress. For the stability of the ship as a whole has been greatly increased by improved adjustment and dimensioning of the girders, and the coefficient of safety in the individual parts of the ship has been greatly equalised. The vibrations in the framework have been reduced to a minimum, in a manner which is really surprising to every one who knows the last War-time ships. The reason for this progress is to be found in a thoroughgoing improvement and a more exacting form of the static method of calculation." On the question of actual flying of airships Dr. Eckener said that gales were regarded by the layman as dangerous to airships, but that, as a matter of fact, a strong wind would never have other effect than to delay or speed-up the trip of an airship, and that it was the vertical air currents that were of more importance, sending the airship upwards rapidly and necessitating the valving of gas, or dropping it dan- gerously close to the ground. A modern airship was, at least, as capable of flying in rough weather as an aeroplane, and on one of the trial trips of the Z.R.III the weather became so rough that an aeroplane which was accompanying the airship had to land. If care was taken to see that the airship was always properly trimmed as the amount of fuel carried was lessened by consumption there was no danger, and the ship could be kept under control in rough weather. The lecturer considered that an airship pilot should have a certain amount of meteorological training. Referring to the necessity for employing technical means of keeping the airship from getting constantly lighter as fuel is consumed, the lecturer expressed preference for the water-recovery method. As regards the danger of lightning, Dr. Eckener thought that provided the valves and ballonettes were gas-tight and the valves were not used actually in a thunderstorm, there was little danger. " In most cases," the lecturer continued, " the airship can circumvent such atmospheric disturbances. As a matter of fact, however, I am convinced that, in order to remove the last vestige of danger in connection with the use of hydrogen, we must and will come to a combination of hydrogen and helium. Then we shall emit hydrogen only when it is absolutely safe, and when we can thereby save the expensive helium." " I have discussed the imaginary and actual dangers at considerable length because of their basic importance, though 1 may add that they did not cause us over much worry or difficulty during the transatlantic trip of the Z.R. III. We were certain that we would be equal to them. However, we were obliged, in the interest of propaganda for airships, to ' put over ' our flight in good style, that is, in the briefest possible time, and it is from this viewpoint that I enter- tained some doubts and concern only with regard to the sufficiency of our fuel supply. I calculated that in all proba- bility we could take along about 30 tons of fuel, provided that we limited crew and ballast to a minimum. This amount of fuel would suffice for about 70 operating hours, if we let all five 400 h.p. engines run full speed. Thus we would have covered about 8,700 km. (4,650 nautical miles) in wind-stillness. But if one counted upon an average of 6 to 7 m.s. of counter-wind—which is not too high an esti- mate in the Atlantic in the fall—we would have covered with our 30 tons benzine only about 7,300 km. But the route via the Azores, which we had chosen in view of the advanced season, is 7,500 km. Thus it was clear that we must at any rate travel with reduced speed, that is, with 300 h.p. to each engine instead of 400 h.p. In this manner we could last 96 hours with 30 tons of benzine and cover 8,600 km. with 6 to 7 m.s. counter-wind, that is, we could make the 7,500 km. in approximately 83 hours. I was a bit concerned over the question whether the 30 tons of benzine would really bring us to the Atlantic coast. For we had to travel over some medium mountains in France at a height of about 850 m. ; we had to figure upon possible high temperatures in the noon hour, and, finally, we had to anticipate a con- siderable cooling of the gas toward evening from 6 to 8 degrees. All this was likely to give our ship an overweight of from 9 to 10 tons towards evening. The dynamic lift of the Z.R. Ill, it is true, amounts to 8 to 9 tons with 6 degrees elevation and 31 m.s. speed, but one does not like to take such a heavy ship out into the sea at night. As soon as only one engine failed even temporarily, we would have had to throw off ballast and benzine. Fortunately, thanks to the alu- minium coat of the outer cover, the gas-overheat was only 2 degrees, and thus we had at any rate gained an amount of approximately 1J tons as against our calculation. " The ship ascended in Friedrichshafen in dense fog, in a temperature of 10° C, 400 m. above the sea level, carrying a useful lift of roundly 39 tons, of which 30 tons were benzine, 2 tons oil and H tons water ballast. During the first half of the flight the "weather was favourable ; over the Azores and over the European Continent there lay a high, and in between a zone with a small disturbance, an outgrowth of a low in the north. Likewise, between Newfoundland and the Bermudas in the Gulf Stream region, there seemed to develop a disturbance of originally indeterminable scope. On our trip across France we had fine weather, with a light south- easterly wind, and made progress with a speed of 105 km. per hour. We crossed the summits of the Cote d'Or as low as possible at a height of only 50 m., and in this way, although over the Cote d'Or, we had a temperature of 21° C, we succeeded in reaching the Atlantic coast with a ship that weighed only 5 tons. This load we could well drag through dynamically, especially inasmuch as we reduced it hourly by 310 kg. by benzine consumption. Towards 7 o'clock in the evening we ran into the afore-mentioned little disturb- ance ; it brought us from 10 to 12 m.s. wind with rain squalls. Under the steep coast of Spain, at Cape Ortegal, the growing wind made itself noticeable in the shape of strong falling gusts which at times caused a more violent yawing and stamping of the ship. An old experience ; over land the air turbulence is greater than over the open sea. Toward midnight we had run through the atmospheric disturbance, the wind having changed from south over west to north-west, and now followed a stretch of finest weather until the next exening about 10 o'clock ; a clear sky and from 2 to 3 m.s. of wind, at first north-easterly, then from a southerly direction. " The navigation was governed by drifting measurements by means of piling bombs, which we dropped, according to necessity, every two to four hours. Navigation was some- what difficult and unsteady during the first part of the night, since the wind changed abruptly both in direction and force, and the next morning we stood about 1° more to the south 203
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