CAB38-23 — Page 145

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SECRET.

REMARKS BY ADMIRAL OF THE FLEET SIR A. K. WILSON.

I.

IN considering what airships can really do, it is necessary to take into account the conditions which limit their weight-carrying capacity.

The total weight-carrying power of the "Schwaben" (see p. 49 of Report and Proceedings of the Technical Sub-Committee of the C.I.D. on Aerial Navigation, 1912), was 21,000 kilom. at sea level and normal temperature.

Deducting its own weight and that of the motor, leaves 5,000 kilom. for all other weights.

If the ship has to rise 3,000 feet she must sacrifice 10 per cent. of her total lifting power, say, 2,100 kilom.

If she has to rise to 6,000 feet she will have to give up 20 per cent., or 4,200 kilom., leaving only 800 kilom. available, which is little more than the weight of the crew, and leaves nothing for fuel.

A shower of rain may cause a further loss of probably another 500 kilom., and a fall of snow much more.

A hot temperature reduces the weight-carrying by about 40 kilom. per degree Fahr., say, roughly, 1 per cent. for each 51° Fahr.

If the gas in the balloon and the surrounding air are at the same temperature, but above the normal 62° Fahr., the lifting power will be reduced in the above proportion.

If the ship starts with the gas at the same temperature as the surrounding air with the weights balanced, and the gas in the balloon is then heated by the sun to a higher temperature than the surrounding air, ite buoyancy will be increased in the above proportion, and hydrogen must be let out to restore the balance. If the gas is then subsequently cooled, weights must be discarded, or there will be negative buoyancy.

In the non-rigid type, the ballonets must be filled before starting sufficiently to reach the maximum height desired without expelling all the air, as if the ship goes higher than this, hydrogen would have to be let out and the weights dropped to balance the loss. The capacity of the ballonets governs the height that can be reached safely, as if the ship starts with the ballonets full, and then rises higher than the ballonots provide for, hydrogen will have to be released, and when the ship comes down it will be impossible to keep up the pressure necessary to maintain the form of the ship.

A further cause of loss of weight-carrying power is that when, as will generally happen in practice, an airship has to be kept inflated for a considerable time, air is liable to leak in at the same time as hydrogen leaks out. This causes a gradual loss of buoyancy which cannot be remedied except by entirely deflating and refilling with pure hydrogen.

The Use of Guns against Airships.

From the above considerations it will be seen that if an airship is required to go a long distance, or to carry considerable additional weight such as guns or bombs of large size, she is not likely to go as high as 3,000 feet. Below this height some of the guns as now mounted in our ships can be given sufficient elevation to hit an airship at ranges which vary with the type of gun and mounting. For example, a 12-inch Mark X gun, with mounting allowing of 13° of elevation, can hit an airship at the height of 3,000 feet at ranges from 11,000 to 6,000 yards. A table should be prepared and circulated to ships showing at what ranges the different types of gun as mounted can be fired at airships at each 500 feet of height up to 3,000 feet, so that they may know under what conditions the guns can be used. The target presented by a Zeppelin is larger than a battleship, and therefore should be easily hit at the ranges at which battle practice is carried out if the same care is taken in range finding and fire control, although the fire cannot be corrected by "spotting."

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