THE CONQUEST OF THE AIR. 35 1 



The propulsion consists of a 25 H.P. 4 cylinder Daimler motor 

 running- at 1,200 revolutions per minute and using less than 10 

 ounces of benzine per H.P. hour at full speed. The speed of the 

 propellors is 300 revolutions. The latter are kept extended, even 

 when the motor is still, by means of springs. The speed of the 

 ship is about 16 miles per hour. 



I shall next deal in a few words with the semi-rigid type. To 

 prevent the balloon from collapsing when the air bags do not fill 

 rapidly enough, and to get better means for hanging up the 

 gondola, a rigid frame or keel is carried below the balloon. This 

 frame is usually made of aluminium or wood. Otherwise these 

 ships are constructed similarly to the non-rigid types. 



Finally I shall deal with the rigid airship of Count Zeppelin. 

 It has a light polygonal girder running from stem to stern, about 

 130 metres long and 12 metres in diameter. The weight of the 

 girder makes a great volume necessarv, and to obtain this without 

 increasing the head resistance unduly, the body is given a great 

 length compared with its diameter, in the ratio of over 10 to i. A 

 single container of this shape would be subjected to dangerous 

 surgings of gas to and fro as either end rose and fell, so Zeppelin 

 adopted a number of small balloons, 16 to 18 in number, separated 

 from one another by partitions, and from the external covering of 

 the balloon by an air space which serves to insulate the gas from 

 the changes in temperature of the atmosphere. The covering for 

 the balloon consists of a double cot-ton fabric, provided with 

 several layers of rubber. This is preferable to a single thick 

 layer, as it is practically impossible to have two pores in the 

 same place in different layers. With 8,000 square metres of 

 fabric it was found that the loss of upward pressure was only 24 

 kgs. per day. This, of course, will be somewhat increased when 

 the balloon is subjected to vibrations, as the coverings will act 

 similarly to sieves. The total contents of the ship is about 15,000 

 cubic metres, with an upward pressure of 16,000 kgs. at sea 

 level. The weight of the ship is 11,000 kgs., leaving 5,000 kgs. 

 for passengers, equipment, ballast, etc. The first model was 

 somewhat smaller, and the motive power was only 16 H .P. The 

 ship had no damping planes and the ascending and descending 

 was accomplished with the aid of a weight, to be shifted on either 

 side of the centre of gravity. Each separate balloon was provided 

 with safety valves ; air ballonets are not required, since excess 

 pressure is communicated to the rigid frame. A number of bal- 

 loons also carried operating valves. The cars or gondolas were 

 fixed below the keel, the propellors were attached in the proper 

 places, i.e. in the plane of the centre of wind pressure. 



In the second model, damping planes were provided, for 

 lateral steering rudders were still placed below the keel. In the 

 third ship, the rudders were placed between the damping or 

 balancing planes ; later on, a finlike plane was added. The fourth 

 ship, which was destroyed after a very successful trio, and after 

 an effective landing at Echterdingen, had various rudders added, 

 especially one at the prow. This, however, did not act, which 

 may be explained bv the presence of an air cushion which is 

 moved along with the ship, so that a rudder, fixed here, is useless. 



