M. Santos Dumont built an extraordinary collection of small airships during a period of several years commencing in 1898. His first effort was a cylinder of varnished Japanese silk, 82½ feet long and 11 feet in diameter, with pointed ends, which gave it a capacity of about 6,300 cubic feet. It was fitted with the usual internal air balloonet and a 3½ horse-power motor-cycle engine weighing 66 pounds. The engine was fitted to an ordinary balloon basket, which hung beneath the envelope and drove a two-blade propeller. The pilot also sat in the basket. The poise of the vessel was controlled by shifting weights, and steering was effected with a silk rudder stretched over a steel frame. In September, 1898, this miniature airship left the Zoological Gardens at Paris in the face of a gentle wind, and performed all sorts of evolutions in the neighborhood.
M. Dumont’s No. 5 was fitted with a four-cylinder, air-cooled motor driving an enormous propeller of 26 feet in diameter, which gave a thrust of 120 pounds at 140 revolutions per minute. There is, however, some difference between this number of revolutions and the 1,400 per minute now generated by all the standard aeronautical motors. Among other novelties water ballast was used and piano wires replaced the old type suspension cords.
No account of the lighter-than-air machine would be complete without mentioning the man after whom the Zeppelins were named. As a matter of fact Count Zeppelin added nothing strikingly new to his airships—he simply made them much larger than any of their predecessors; thus increasing the net lifting power and multiplying the number of engines and the horse-power.
Count Ferdinand von Zeppelin first began to experiment in 1898. His first rigid dirigible was 410 feet and the gas-bags contained 400,000 cubic feet of hydrogen, and the net lifting power, after allowing for the engines, fuel, gear, etc., was about two tons. The framework was of aluminum latticework divided into seventeen compartments, fifteen of which had gas-bags. Two cars were attached and in each was a 16 horse-power German Daimler gasoline motor driving two propellers, and the machine gained a speed of 15 miles an hour, which was far in advance of any airship of that period.
By this time practically all the fundamentals of construction of dirigibles had been incorporated in these airships. Further refinements were made, more engines and balloonets added, and the length of the dirigible and the volume of hydrogen gas used for inflation was increased, as was also the horse-power, but nothing more in the way of radical changes was employed to the end of the Great War. Therefore a description of the Zeppelin which was brought down in England will serve as an excellent idea of the size of these mammoth airships.
The Zeppelin forced to land in Essex measured from 650 feet to 680 feet in length and measured 72 feet across its largest diameter. The vessel was of the stream-line form, with a blunt, rounded nose, and a tail that tapered off to a sharp point. The framework was made of longitudinal latticework girders, connected together at intervals by circumferential latticework ties, all made of an aluminum alloy resembling duraluminum. The whole was braced together and stiffened by a system of wires, arrangements being provided by which they could be tightened up when required. The weight of the framework is reckoned to be about 9 tons, or barely a fifth of the total of 50 tons attributed to the airship complete with engines, fuel, guns, and crew. There were 24 balloonets arranged within the framework, and the hydrogen capacity was 2,000,000 cubic feet.
A cat-walk, an arched passage with a footway nine inches wide, running along the keel enabled the crew, which consisted of twenty-two men, to move about the ship and get from one gondola to another. This footway was covered with wood, a material which, however, was evidently avoided as much as possible in the construction of the ship. The gondolas, made of aluminum alloy, were four in number; one was placed forward on the centre line, two were amidships, one on each side, and the fourth was aft, again on the centre line.
The vessel was propelled—at a speed, it is thought, of about sixty miles an hour in still air—by means of six Maybach-Mercedes gasoline engines of 240 horse-power each, or 1,440 horse-power in all. Each had six vertical cylinders with overhead valves and water cooling, and weighed about 1,000 pounds. They were connected each to a propeller shaft through a clutch and change-speed gear, and also to a dynamo used either for lighting or for furnishing power to the wireless installation. One of these engines with its propeller was placed at the back of the large forward gondola, two were in the amidships gondolas, and three were in the aft gondola. In the last case one of the propellers was in the centre line of the ship, and the shafts of the other two were stayed out, one on either side. With the object of minimizing air resistance the stays were provided with a light but strong casing of two or three ply wood, shaped in stream-line form. The gasoline tanks had a capacity of 2,000 gallons, and the propeller shafts were carried in ball bearings. The date, July 14, 1916, marked on one of them, is thought to indicate the date of the launching or commissioning of the vessel.
Forward of the engine-room of the forward gondola, but separated from it by a small air space, was first the wireless operator’s cabin and then the commander’s room. The latter was the navigating platform, and in it were concentrated the controls of the elevators and rudder at the stern, the arrangement for equalizing the levels in the gasoline and water tanks, the engine-room telegraphs, and the switchboard of the electrical gear for releasing the bombs. Provision was made for carrying sixty of the latter in a compartment amidships, and there was a sliding shutter, worked from the commander’s cabin, which was withdrawn to allow them to fall freely. Nine machine-guns were carried. Two of these, of 0.5-inch bore, were mounted on the top of the vessel, and six of a smaller caliber were placed in the gondolas—two in the forward, one each in the amidships ones, and two in the aft one. The ninth was carried in the tail.
The separate gas-bags were a decided advantage over the free balloon and earlier airships which carried all the gas in one compartment, for if the latter sprang a leak for any reason it had to descend, whereas the Zeppelin could keep afloat with several of the separate compartments in a complete state of collapse.