ENGINEERING BEFORE AND AFTER WAR 49 



it may be opportune to make the following- observations 

 on the comparative utility of aeroplanes and airships for 

 commercial purposes. In the case of the aeroplane, the 

 weight per horse-power increases with the size, other 

 things being equal. This increase, however, is met to some 

 extent by a multiplicity of engines, though in the fusilage 

 the increase remains. 



On the other hand, with the airship the advantage in- 

 creases with the size, as in all ships. The tractive effort 

 per ton of displacement diminishes in inverse proportion 

 to the dimensions, other things, including the speed, being 

 the same. Thus, an airship of 750 feet length and 60 

 tons displacement may require a tractive force of 5 per 

 cent., or 3 tons, at 60 miles per hour; while one of 1,500 

 feet in length and 8 X 60 = 480 tons displacement would 

 only require 2% per cent. X 480 = 12 tons at the same 

 speed, and would carry fuel for double the distance. 



With the same proportion of weight of hull to displace- 

 ment, the larger airship would stand double the wind pres- 

 sure, and would weather storms of greater violence and 

 hailstones of greater size. It would be more durable, the 

 proportional upkeep would be less, and the proportional 

 loss of gas considerably less. In other words, it would 

 lose a less proportion of its buoyancy per day. It is a 

 development in which success depends upon the project 

 being well thought out and the job being thoroughly well 

 done. The equipment of the airsheds with numerous 

 electric haulage winches, and all other appliances to make 

 egress and ingress to the sheds safe from danger and ac- 

 cident, must be ample and efficient. 



The airship appears to have a great future for special 

 commerce where time is a dominant factor and the de- 

 mand is sufficient to justify a large airship. It has also 

 a great field in the opening up of new countries where 

 other means of communication are difficult. The only 

 limitation to size will be the cost of the airship and its 

 sheds, just as in steam vessels it is the cost of the vessels 



