Fig. 79.—Control platform of an Airship.
A.A. Wheels operating elevating-planes and rudder; B. Height recorder; C. Speaking-tube to communicate with engineers.
Fig. 80.—Hull of a Zeppelin during construction.
Craft of the semi-rigid type provide a link between small, non-rigid ships and the very large machine which is built with an entirely rigid framework, and has its example in the Zeppelin. The maker forms a skeleton hull of aluminium or some light metal alloy, a method that is shown in [Fig. 80]. The hull of a Zeppelin, slightly more than 500 feet in length, is sheathed with tightly stretched fabric; and within it are the gas-containers—a row of seventeen separate balloons, each in a compartment by itself, and containing a total of nearly 1,000,000 cubic feet of gas—which give these airships a lifting power of close upon 30 tons. The arrangement of the gas-holders, and the general outline of the machine, may be observed from [Fig. 81]. The vessel offers comparatively little resistance to the air, despite its size, and this is due to the finely tapering shape of the hull; while its rigidity allows it to be driven at speeds of more than 50 miles an hour. The lifting capacity, also, enables long flights to be made. Taking up crew and petrol, such a craft can remain aloft for several days, and travel distances of more than 1000 miles.
Fig. 81.—A Zeppelin Airship.
A.A. Rigid hull covered by fabric; B. Section showing the skeleton framework of hull; C. Arrangement of the interior gas chambers; D. Elevating-planes; E.E. Rudders; F.F. The two cars containing engines and crew; G. Passage-way between the cars; H. One of the propellers, of which the craft has four—two at the front of the hull, upon either side, and two at the rear.