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Military


Airship Sheds

The construction of airship sheds had been an important item in the expense of airship work. The cost of the shed increases very rapidly with height and with the span, both of which must be considerable with any but the very small ships. Apart from tHe cost of the shed, there is considerable difficulty in taking a ship into the shed in any but very calm weather. When a wind is blowing across the mouth of the shed, the airship has to be hauled broadside on to the wind in order to pass in through the door, and this represents a very difficult operation when the wind is of considerable strength or of a gusty nature. In order to afford protection during this operation, all early airship sheds were provided with windscreens running from the corners of the shed outwards parallel to the axis. These screens were of a height nearly equal to that of the shed, and afforded considerable protection against the horizontal force of the wind. They, however, caused a serious eddy to be formed, which produced a vertical disturbance on the ship nearly as difficult to overcome as the horizontal force which would have existed had there been no wind-screens present. Experiments were carried out with the wind-screens formed of expanded metal, and with screens of corrugated iron in which 30 % of the sheeting had been omitted. These screens, although they reduced the horizontal wind to a smaller extent than the solid screens, avoided the serious vertical air disturbance and were, for that reason, considerably preferable.

Experience in Germany had, however, shown that a system of rails provided with easily running trolleys was the most satisfactory system of supporting the ship against sideways forces. These rails ran out from the corners of the shed parallel to the axis, and the side-guys of the ship were attached to trolleys running on these rails. The support of the ship obtained in this way is so good that wind-screens are rendered unnecessary, and the vertical air disturbance connected with them is thereby avoided. Even with this system of handling rails, the housing of an airship presents considerable difficulties. A landing party of several hundred men is required to receive a 60-ton airship on the landing ground, to carry her to the end of the handling rails and to haul her round parallel to the rails. The air in the neighbourhood of the shed is necessarily so disturbed that considerably greater difficulty is experienced near the shed than when on the open landing ground or in the neighbourhood of a mooring mast. The difficulties connected with airship sheds are, therefore, considered to be so great that the shed must only be regarded as the dock, the mooring mast being regarded as the normal method of securing an airship between flights.

When secured to the mast the airship can be supplied with gas, water ballast and fuel. The passengers can be passed up the mast by a lift and can walk through the bow of the ship down to the cabin. The airship appears to behave satisfactorily in any wind. The most difficult conditions to meet are those in which there is no wind but rapid changes of temperature which affect the lift of the ship. This necessitates rapid adjustment of the ballast in the ship by taking in or discharging water. As long as there is a considerable wind the trim can be regulated by the elevators, as in flight.

Attempts have been made to anchor a ship to the ground by a single wire. This operation would have considerable advantages for a ship which became broken down and required to avoid drifting with the wind. At sea a drogue can be lowered into the water, and the ship will ride to it satisfactorily provided she is correctly trimmed some five degrees up by the bow in order to derive the necessary dynamic lift. It is, however, necessary to steer the ship continuously while secured in this way, exactly as though in flight. Anchoring to the ground is a considerably more difficult problem. A grapnel cannot obtain a sufficiently firm hold to resist the impulsive upward pull in the airship trail rope. Experiments were carried out with a form of dropping grapnel consisting of a large, suitably shaped weight dropped from a height of some 200 feet. This grapnel obtained a satisfactory hold either on very hard ground or on soft ground where the penetration was very deep. The hold was, however, quite unyielding, and the shock produced on the ship when thus checked was far too serious. Various forms of friction device to allow a gradual check to be brought on the ship were tried, but were never found sufficiently satisfactory for adoption.





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Page last modified: 11-07-2011 15:29:15 ZULU