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Aviation History
1925
1925 - 0117.PDF
FEBRUARY 26, 1925 which have been devised for ease of measurements. The author drew attention to the fact that recently photo-elastic laboratories have been established in various parts of the world, some of which are especially interested in applications to aeronautical problems of stress distribution, and, since it seems probable that this will lead to developments in this field, he made special reference as to its possible uses. Several interesting illustrations were given—such as the case of the simple stiff joint, an aeroplane strut, eye-bolts, and finally, the case of the problem of the stress in a main cross-frame of a rigid airship. Some suggestions were also made as to the best ways of obtaining the stress distribution in such a case by large- scak- photo-elastic experiments in a special form of polariscope. Prof. Coker then dealt with the design of various parts in order to obtain the least weight of aeroplane and airship framing, and concluded with a description of some specific cases in which the general nature of the problem and the methods of solution were outlined. Some extremely interesting pictures of gear-wheel models were shown, in which the stress distri- bution was clearly shown under various conditions. At the conclusion of the paper Dr. Thurston expressed the opinion that photo-elastic methods would be of great value in connection with aeronautics, and asked if it would be possible to render wood—which material aircraft constructors had to employ very extensively—transparent, and so obtain an insight as to its somewhat peculiar behaviour under stress by means of the polariscope. Failing this he suggested coating the surface of the wood with silver or the like and placing over this the transparent material, to which the stresses in the wood might be transmitted, and taking the " polarised readings " from this. Another suggestion made by Dr. Thurston was to the effect that it might be possible to" build up a structure as near as possible to that of wood—consisting of numerous transparent tubular members " stuck together " —and in this way obtain polarised pictures. AMERICA'S SUPER-ZEPPELIN IN our issue of December 18 last, we published a report to the effect that U.S. Naval and Air experts had laid before Congress plans for an airship of about 6,000,000 cub. ft. capacity. This week we are able, through the courtesy of our American contemporary, Slipstream, to give further par- ticulars of this monster airship. These details have been given out by Mr. P. \Y. Litchfield, Vice-President and General Manager of the Goodyear-Zeppelin Corporation, and may, therefore, be taken as authentic. Working plans for this super-airship, which will be twice as large as any airship ever built, and slightly larger than the two 5,000,000 cub. ft. airships being built for the British Imperial service to India, were started with the arrival in America last year of Dr. Karl Arnstein, formerly chief engineer to the German Zeppelin Co., and a selected staff of twelve technical men from. Friedrichshafen—the birthplace of the Zeppelin. Dr. Arnstein, under whose direction nearly 100 Zeppelins were constructed in Germany, now holds a similar capacity with the Goodyear-Zeppelin Corp., a sub- sidiary of the Goodyear Tire and Rubber Co., which took over Zeppelin rights for North America. In answer to the question " Why build an airship of such large capacity as 5,000,000 cub. ft., when smaller ships like the ' Shenandoah ' and the Z.K.3, or ' Los Angeles,' have shown themselves capable of accomplishing successfully big flights, such as the 9,000-mile trip twice across the United States, and the 5,000-mile non-stop journey from Germany to America," Mr. Litchfield makes the following statement :— The most important consideration is that the airship reaches its highest efficiency in the larger units. The larger the air- ship is, the higher is the proportion of useful lift in com- parison to size. The earliest Zeppelins carried only from 10 to 20 per cent, of their weight uschil load, while the Z.R.3, inflated with gas and under normal temperature and pressure conditions, weighed when empty about 45 tons, but was able to lift a total weight of some 90 tons—or a useful load of 50-60 per cent. A ship twice the size of the Z.R.3 would not require twice the amount of fuel or twice as large a crew, and would thus have a considerable larger percentage of space for passengers, mail, etc. A ten-million cub. ft. airship could carry a proportionately greater pay load than a five-million cub' ft. ship. However, it is logical to start first in the intermediate size of a five to six-million cub. ft. ship and learn what problems are involved there before going to the next step. In taking up the design of the five to six-million cub. ft. ship, writes Mr. Litchfield, they are undertaking a new problem, and there are various considerations that must be taken into account. Whether the first requirements of America would be for a military or commercial airship is a primary factor, involving many variations in design. If the ship is a commercial one, built for speed, then some- thing can be sacrificed in the pay load it may carry. If it is to be built primarily for transport, and the matter of 10 or 15 in.p.h. difference in the rated speed of the engines is not important the engineers must include that fact in their computations. If the ship is designed for travel over-land sav_ between the Atlantic and Pacific Oceans—the altitudeto be reached or the ceiling of the ship is an important factor, for on the journey from west to east the airship must cam- its maximum weight over the Rocky Mountains, and in the higher altitudes the air pressure is less and the temperature is lower both factors affecting the lifting power of the gas. If +hc ship is designed for coast patrol with the fleet, making comparatively short, but fast, scouting trips, it will have different requirements from a ship that is to carry passengers, mail and express across the Atlantic without opportunity for refueling en route. These and other primary facts have to be studied before the final lines of design can be settled, but it is possible to set down in approximate figures at least the general limitations somewhere within which the proposed ship will find itself. First and foremost the capacity of the gas bags is set at being between five and six million cub. ft. The " Shenaji- doali " is 680 ft. long and 78 ft. in diameter. The Z.R.3, somewhat shorter and fatter, is 660 ft. long and 101.6 ft. in diameter. This gives a ratio of slenderness for the " Shen- andoah " of 8.7, and the Z.R.3 ratio is about 7.2. The proposed super-Zep. may be between 860 and 930 ft. long, the maximum diameter 115 to 120 ft., with the overall height from the ground (i.e., including control car) 10 ft. more, and with a slenderness ratio of about 7.5. Let the power required to drive this big ship be set down at 4,000 h.p., as against 1,500 h.p. for the " Shenandoah " and 2,000 h.p. for the Z.R.3. With the engines this size a ship should develop a speed of 80 to 85 m.p.h., and driven at a maximum speed with a full fuel reserve, passengers, freight and mail, should have no difficulty in making a 6,000-mile non-stop flight. If driven at a cruising speed of 75 m.p.h., it could go, say, 8.000 miles non-stop. As to pay load, it might carry, say, from. 50 to 125 pas- sengers, 3 to 6 tons of mail, and up to 12 tons of freight over these distances. What will the ship be like ? Assume it is designed for overseas transport as a commercial airship, supplementing the steamship service by giving a two-day service between New York and London for that class of passengers to whom time- is important and who would make many more trips a year if they could make the round trip to Europe and back in a week or ten days. We may visualise a passenger cabin, extending along the keel of the hull, with a promenade deck and chairs, comfortable berths, dining-room service, shower baths and the like, furnishing a pleasant and easy journey, without sea-sickness or other discomforts of present methods of travel. As regards fares, Mr. Litchfield points out that, while thousands of flights were made by Zeppelin airships in the past, when some 35.000 passengers were tarried without accident or mishap, the experience in operating airship services has been too limited to draw final conclusions as to the cost of airship travel. What may be said is that the Zeppelin airships offer a new and faster method of long-distance transport, and that interest- ing developments are ahead. America is now able to draw upon the accumulated experience of twenty-five years of the Zeppelin organisation in construction and operation of air- ships. It has the added advantage of American factory methods of construction, etc., plus the fact of a great con- tinent and two great oceans to operate over without having to cross the borders of another nation. In conclusion, it maybe of interest to note that Dr. Hugo Eckener, head of the Zeppelin plant and commander of the Z.R.3 on its delivery flight, will be a member of the board of directors for the Goodyear-Zeppelin Company, his presence and that of Dr. Arnstein and E. A. Lehman (formerly of the Zeppelin Company) being an assurance that the full resources and experience of successful Zeppelin operation will be at America's disposal. 117
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