GAS FOR AIRSHIPS.

Taranaki Daily News, 22 February 1922, Page 8

GAS FOR AIRSHIPS.

POSSIBILITIES OF HELIUM. AMERICAN EXPERIMENTS. OVERCOMING FIRE DANGERS. London, Dec. 29. Reports have been received from the United States concerning tests made with the naval non-rigid airship C 7, inflated with heli.um gas. As a result of the experiments that are being made relative to buoyancy, permeability of fabric, and valve-control it is considered the practical use of helium as a gas for the inflation of airships has been demonstrated beyond doubt, tn addition to the very great advantage of non-in-flammability, the use of helium facili-

tates operating, as it does not expand and contract nearly as rapidly as hydrogen. besides which the diffusion through fabric is much less. Helium gas has 92 per cent, of the lifting power of hydrogen gas. The natural gas wells in the United States afford a practical monopoly of the known sources of supply of helium gas. According to the estimate,. helium is escaping into the atmosphere at the rate of 1,250,000 cubic feet a day, or at volume sufficient to fill four large airships in a week. The gas is only 5 per cent, heavier than hydrogen; but this disadvantage is rather * greater than the figure shows, because it has not yet been possible to secure so high a degreee of purity as is attainable with hydrogen. Nevertheless, the employment of helium would, it is pointed out, probably permit weightsaving modifications in design, owing to the reduction of the fire danger, and this might malye up for the deficiency in lift. It is possible to make a non-in-flammable mixture of about sev pprts of hydrogen to one of helium, but further tests will be necessary before deciding whether this would be practicable in airship work. For coming experiments it will be necessary in every possible way to prevent the leakage of gas through the airship envelope and valves, and the work that is being done may. therefore, prove to be of value also to hydrogen airships. * The cause of fire in airships, apart from enemy action, is at least as likely, and probably more likely, to be petrol fumes, so that for commercial airship the problem of the moment is rather to find a less volatile fuel than petrol, and this will in all probability be found before the supply of helium is sufficient for general use.

An explosion is caused by a mixture of hydrogen and air meeting a spark. In the case of a small leak in the envelope, the escaping gas from which becomes ignited, the danger is due to the rapid enlargement of the aperture. Some contrivance preventing this rapid enlargement would therefore be of enormous value. It has been proposed to use helium only as an outer layer; thus acting as a protective fireproof covering; and it is also almost certainly possible to contrive a protective sheath filled with some fire-quenching matter, such as the exhaust tames from the engines. The weight of extra envelopes is. however, a serious drawback, for with some increase of airship speed, which is desirable, it is unlikely that any saving of weight can be effected in the framework. It is suggested that one way of preventing fire, so far as the hull is concerned, would be to have a small helium compartment adjoining each o£ the engine cars, so that fire or sparks arising in them would not reach the hydrogen.