MILITARY AERONAUTICS SQUIEE. 121 



SO that when the gas expands all the air is driven out of the ballonet 

 before there is any loss of gas. The ballonet valves open at a pres- 

 sure of about 0.78 inch of water, the gas valves at about 2 inches. 



Stability. — Vertical stability is maintained by means of fixed 

 horizontal planes. One having a surface of 150 square feet is attached 

 at the rear of the gas bag, and due to its distance from the center of 

 gravity is very efficient. The elliptical frame attached under the gas 

 bag has an area of 1,055 square feet, but due to its proximity to the 

 center of gravity has little effect on the stability. Just behind the 

 elliptical frame is an arrangement similar to the feathering on an 

 arrow. It consists of a horizontal plane of 150 square feet and a 

 vertical plane of 113 square feet. To maintain horizontal stability, 

 that is, to enable the airship to move forward in a straight line with- 

 out veering to the sides, fixed vertical planes are used. One runs from 

 the center to the rear of the elliptical frame and has an area of 108 

 square feet. 



In addition to the vertical surface of 113 square feet at the rear of 

 the elliptical frame, there is a fixed plane of 150 square feet at the 

 rear of the gas bag. To fasten the two perpendicular planes at the 

 rear of the gas bag, cloth flaps are sewed directly on the gas bag. 

 Nickel-steel tubes are placed in the flaps which are then laced over 

 the tubes. With these tubes as a base a light tube and wire frame- 

 work is attached and waterproof cloth laced on this framework. 

 Additional braces run from one surface to the other and from each 

 surface to the gas bag. The rudder is at the rear under the gas bag. 

 It has about 150 square feet and is balanced. 



A movable horizontal plane near the center of gravity, above the 

 car, is used to produce rising or descending motion, or to prevent an 

 involuntary rising or falling of the airship due to expansion or con- 

 traction of the gas or to other causes. After the adoption of this 

 movable horizontal plane the loss of gas and ballast was reduced to a 

 minimum. Ballast is carried in 10 and 20 pound sand bags. A pipe 

 runs through the bottom of the car from which the ballast is thrown. 



There are two long guide ropes, one attached at the front of the 

 elliptical frame and the other on the car. On landing, the one in 

 front is seized first, so as to hold the airship with the head to the wind. 

 The motor may then be stopped and the descent made by pulling 

 down on both guide ropes. A heavy rope, 22 feet long, weighing 110 

 pounds, is attached on the end of a lG4-foot guide rope. This can be 

 dropped out on landing to prevent coming to the ground too rapidly. 

 The equipment of the car includes a " siren," speaking trumpet, car- 

 rier pigeons, iron pins and a rope for anchoring the airship, reserve 

 supply of fuel and water, and fire extinguisher. 



After being enlarged in September, 1907, the Patrie made a num- 

 ber of long trips at an altitude of 2,500 to 3,000 feet. In November, 



