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They have been fostered upon a smaller but equally effective scale. The semi-rigid Parseval and Gross craft have met with whole-hearted support, since they have established their value as vessels of the air, which is tantamount to the acceptance of their military value.
While out cruising with a crew of four officers one of the propeller blades was suddenly fractured, and, flying off with immense force, it entered the balloon, which it ripped to pieces. The majestic craft crumpled up and crashed to the ground, killing its crew in its fall. In the illustration facing p. 17, of a Lebaudy air-ship, we have a good type of the semi-rigid craft.
It is the introduction of this rigid girder which is responsible for the descriptive generic term of "semi-rigid." On the other hand the "non-rigid" type may be roughly described as a pisciform balloon fitted with propelling machinery, inasmuch as the car containing the driving machinery is suspended from the balloon in the manner of the car in the ordinary drifting vessel.
The balloon is divided into three compartments, so that the heavier air does not move to one part of the balloon when it is tilted. In the picture there is shown the petrol storage-tank, which is suspended immediately under the rear horizontal plane, where it is out of danger of ignition from the hot engine placed in the car. Hitherto we have described the rigid and semi-rigid types of air-ships.
Although the rigid type never has met with favour in France, there is yet a solitary example of this system of construction the Spiess, which is 460 feet in length by 47 feet in diameter and has a displacement of 20 tons. The semi-rigid craft are represented by the Lebaudy type, the largest of which measures 293 feet in length by 51 feet in diameter, and has a displacement of 10 tons.
For work farther out at sea and in all weathers, airships known as the coast patrol type, and more commonly as 'coastals, were built, and later the 'N.S. or North Sea type, still larger and more weather-worthy, followed. By the time the last year of the War came, Britain led the world in the design of non-rigid and semi-rigid dirigibles.
As to the former, I think it is pretty well agreed that the bar only one, please answers the purpose of a support and vibrator, as opposed to the soundpost, which is of a quite opposite nature, being semi-rigid and a conductor of sound. I will try to make this very vital point clear to you.
Sufficient to say that Tom's craft consisted first of a great semi-rigid bag, or envelope, made of specially prepared oiled silk and aluminum, to hold the gas, which was manufactured on board. There were a number of gas-tight compartments, so that if one, or even if a number of them burst, or were shot by an enemy, the craft would still remain afloat.
Among them are the semi-rigid Parseval and Gross types which found great favour among the military authorities during the war. The latter is merely an adaptation of the highly successful French ship the Lebaudy, but the Parseval is the result of a slow evolution from an ordinary balloon.
As is well known Zeppelin evolved what may be termed an individual line of thought in connection with his airship activities. He adopted what is known as the indeformable airship: that is to say the rigid, as opposed to the semi-rigid and flexible craft.
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