Ballonet

A ballonet is a balloon-like air bag in the interior of a semi-rigid airship, or baffle, with the aid of which the change in volume of the carrier gas is equalized. It ensures that the inside of the float always there is a slight positive pressure, to thereby hold him tightly. This overpressure is only a few millibars, usually about five millibars.

It was proposed this solution for the first time in 1784 by Jean -Baptiste Meusnier de la Place ( 1754-1793 ).

Ballonets inflate within the case with air, which is branched off from the air current of the drive propeller. In some models but they are also separate blower for use. The size of such ballonets is in the fully inflated condition usually about 25 - 40 percent of the total shell volume.

The carrier gas changes its volume by changes in outside temperature or the external pressure ( eg by changes in altitude or weather phenomena ) according to the general gas equation:

(p = pressure, V = volume, T = temperature)

Most airships two ballonets are provided, which are arranged in the vicinity of the bow and the stern in the shell to enable a static trim of the airship to the transverse axis, without additional ballast. The pilot can control the filling and emptying by appropriate valves and shift the focus of the entire airship by different degrees of filling of the ballonets.

If the pressure of the lifting gas within the envelope of a limit, then valves automatically open to the ballonets and let air into the environment in order to give room for expansion the gas. The height at which the ballonets are empty and the carrier gas occupying the entire volume of the sleeve is referred to as a baffle height. Increasing an airship about its bounce height, the pressure inside will increase further because with decreasing pressure outside the supporting gas volume can not be increased. Automatic safety valves then let off lifting gas to prevent the bursting of the shell in height.

One of the most ballonets has a ripcord, which allows to open the ballonet within the shell. This is used when the shell itself has a leak and carrier gas escapes. Then air can after opening the ballonets blown directly into the shell and the inner pressure and thus the shape and controllability of the ship obtained until it has landed.

Also, the Zeppelin NT as a semi-rigid airship has two ballonets.

• Airship Technology