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The immediate cause may have been a leaky valve permitting the gas to escape, or a faulty air-pump which made prompt filling of the ballonet impossible. But the effect of these flaws was to deprive the balloon of its rigidity, cause it to buckle, throwing the cordage out of gear, shifting stresses and strains, and resulting in ultimate breakdown.
It appears to be rearing up on end, as if the extremity saddled with the ballonet were weighted. British and French captive balloon authorities are disposed to discount the steadying effect of this attachment, and, indeed, to maintain that it is a distinct disadvantage.
These endeavours culminated in the Parseval-Siegsfeld captive balloon, which has a quaint appearance. It has the form of a bulky cylinder with hemispherical extremities. At one end of the balloon there is a surrounding outer bag, reminiscent of a cancerous growth. The lower end of this is open. This attachment serves the purpose of a ballonet.
The balloon frame was divided into seventeen compartments, each of which held a ballonet filled with hydrogen gas. The purpose of this was similar to the practice of dividing a ship's hulls into compartments. If one or more of the ballonets, for any reason, were injured the remainder would keep the ship afloat.
The chief interest in his design, though it never materialized, lies in the fact that it provided for a double envelope and was the precursor of the ballonet. The first man-carrying airship was built by Henri Giffard in 1852. It had a capacity of 87,000 cu. feet, a length of 144 feet, a 3 horse-power engine, and a speed of 6 miles an hour.
The balloon began to collapse in the middle. Cords subjected to unusual stress began to snap. The air pump, which should have pumped the ballonet full of air to keep the balloon rigid failed to work. Seeing that he was about to fall into a field in which his drag rope was already trailing the imperilled airman had a happy thought. Some boys were there flying kites.
The ballonet became particularly valuable as soon as airship construction became general, and it was in the course of advance in Astra Torres design that the project was introduced of using the ballonets in order to give inclination from the horizontal.
The result was so swift a descent that he dislocated his wrist on landing. Meusnier, toward the end of the eighteenth century, was first to conceive the idea of compensating for the loss of gas due to expansion by fitting to the interior of a free balloon a ballonet, or air bag, which could be pumped full of air so as to retain the shape and rigidity of the envelope.
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