British Airships, Past, Present and Future | Page 8

as on occasions they have been known to jam, and the loss of gas has not been discovered until the ship had become unduly heavy. Pressure should be kept as constant as possible. Most airships work up to 30 millimetres as a maximum and 15 millimetres as a minimum flying pressure. During a descent the pressure should be watched continuously, as it may fall so low as to cause the nose to blow in. This will right itself when the speed is reduced or the pressure is raised, but there is always the danger of the envelope becoming punctured by the bow stiffeners when this occurs. HOUSING ACCOMMODATION FOR AIRSHIPS, ETC. During the early days of the war, when stations were being equipped, the small type of airship was the only one we possessed. The sheds to accommodate them were constructed of wood both for cheapness and speed of construction and erection. These early sheds were all of very similar design, and were composed of trestles with some ordinary form of roof-truss. They were covered externally with corrugated sheeting. The doors have always been a source of difficulty, as they are compelled to open for the full width of the shed and have to stand alone without support. They are fitted with wheels which run on guide rails, and are opened by means of winches and winding gear. The later sheds built to accommodate the rigid airship are of much greater dimensions, and are constructed of steel, but otherwise are of much the same design. The sheds are always constructed with sliding doors at either end, to enable the ship to be taken out of the lee end according to the direction of the wind. It has been the practice in this country to erect windscreens in order to break the force of the wind at the mouth of the shed. These screens are covered with corrugated sheeting, but it is a debatable point as to whether the comparative shelter found at the actual opening of the shed is compensated for by the eddies and air currents which are found between the screens themselves. Experiments have been carried out to reduce these disturbances, in some cases by removing alternate bays of the sheeting and in other cases by substituting expanded metal for the original corrugated sheets. It must be acknowledged that where this has been done, the airships have been found easier to handle. At the outbreak of war, with the exception of a silicol plant at Kingsnorth, now of obsolete type, and a small electrolytic plant at Farnborough, there was no facility for the production of hydrogen in this country for the airship service. When the new stations were being equipped, small portable silicol plants were supplied capable of a small output of hydrogen. These were replaced at a later date by larger plants of a fixed type, and a permanent gas plant, complete with gasholders and high pressure storage tanks was erected at each station, the capacity being 5,000 or 10,000 cubic feet per hour according to the needs of the station. With the development of the rigid building programme, and the consequent large requirements of gas, it was necessary to reconsider the whole hydrogen situation, and after preliminary experimental work it was decided to adopt the water gas contact process, and plants of this kind with a large capacity of production were erected at most of the larger stations. At others electrolytic plants were put down. Hydrogen was also found to be the bye-product of certain industries, and considerable supplies were obtained from commercial firms, the hydrogen being compressed into steel cylinders and dispatched to the various stations. Before concluding this chapter, certain words must be written on parachutes. A considerable controversy raged in the press and elsewhere a few months before the cessation of hostilities on the subject of equipping the aeroplane with parachutes as a life-saving device. In the airship service this had been done for two years. The best type of parachute available was selected, and these were fitted according to circumstances in each type of ship. The usual method is to insert the parachute, properly folded for use, in a containing case which is fastened either in the car or on the side of the envelope as is most convenient. In a small ship the crew are all the time attached to their parachutes and in the event of the ship catching fire have only to jump overboard and possess an excellent chance of being saved. In rigid airships where members of the crew have to move from one end of the ship to the other, the harness is worn and parachutes are disposed in the keel and cars as are lifebuoys in seagoing vessels. Should an emergency arise, the nearest parachute can