130 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1908. 



hang limp when not turning. "When the motor is running, these 

 blades, which are carefully weighted with lead at certain points, 

 assume the proper position due to the various forces acting. The 

 diameter is 13f feet. The propeller is placed above the rear of the 

 car near the center of resistance. Shaft transmission is used. The 

 propeller makes 500 revolutions per minute to 1,000 of the motor. 

 There is a space of 6^ feet from the propeller blades to the gas bag, 

 the bottom of the car being about 30 feet j'rom the gas bag. This 

 propeller has the advantage of being very light. Its position, so far 

 from the engine, necessarily incurs a great loss of power in trans- 

 mission. 



The steering wheel at the front of the car has a spring device for 

 locking it in any position. 



The 1908 model of this airship was constructed for the purpose 

 of selling it to the Government. Among other requirements is a 

 twelve-hour flight without landing and a sufficient speed to maneuver 

 against a 22-mile wind. A third and larger air ship of this type is 

 now under construction. 



The Zeppelin. 



The Zeppelin airship, of which there have been four, differs from 

 all others in that the envelope is rigid. Sixteen separate gas bags are 

 contained in an aluminum alloy framework having 16 sides, covered 

 with a cotton and rubber fabric. The pressure of the air is taken up 

 by this framework instead of by the gas bags. The gas bags are not 

 entirely filled, thus leaving room for expansion. 



The rigid frame is 446 feet long, 42^ feet in diameter, and has 

 ogival-shaped ends. It is braced about every 45 feet by a number of 

 rods crossing near the center, giving a cross section resembling a 

 bicycle wheel. Vertical braces are placed at intervals the entire 

 length of the frame. The 16 gas bags are completely separated from 

 each other by partitions of sheet aluminum. Under the framework 

 is a triangular truss running nearly the entire length, the sides of 

 the triangle being about 8 feet. The total volume of the gas bags is 

 400,000 cubic feet, which gives a gross lift of about 32,000 pounds. 



Suspension. — The two cars are rigidly attached directly to the 

 frame of the envelope and a very short distance below it. 



Cars. — The two cars are built like boats. They are about 20 feet 

 long, 6 feet wide, 3^ feet high; are placed about 100 feet from each 

 end and are made of the same aluminum alloy. To land the air- 

 ship, it is lowered until the cars float on the water, when it can be 

 towed like a ship. A third car is built into the keel directly under 

 the center of the framework, and is for passengers only. 



Motors. — The power is furnished by two 110-horsepower Daimler- 

 Mercedes motors, one placed on each car. Each weighs about 550 

 pounds ; sufficient fuel for a sixty-hours' run can be carried. 



