Information about "non-rigid airships"

pressurized airships
Airships, which get their shape only in cause of the pressure of the lifting-gas inside the envelope are called airships of the non-rigid type. All extensions, like the fins and the control car, are attached to the envelope. The driving elements are attached to the gondola/control car. These non-rigid airships have a long tradition and were never totally droped out of sight.(especially in USA) The first blimps, which had been really suitable and do also exist in  'modern' versions in the present, were invented by August von Parseval. (click here for more information about Parseval-Airships)
 
One of the most important elements of a non-rigid airship is the ballonet-system. A ballonet is an airbag (one or two of them) inside the envelope, which provided with air from a blower or direct over ducts from the propellers of the engine unit. The air could be removed from the ballonet through valves.
 
The ballonets are used for:


  • The lifting gas increases its volume in cause of higher temerature or a lower airpressure, also decreases its volume  in cause of lower temperature or higher airpressure. If an airship (without a ballonet) is full of gas and also tight, which must be or it won't be suitable, on the ground and starts now, increases its altitude, so the lifting gas inside the envelope will increase its volume in cause of the lower airpressure in a higher altitude. The envelope will burst or the gas will leak through an overpressure valve. If you are going to land this airship, the gas will decrease its volume and the envelope will get slack and there's no chance to control this airship. Therefor you use ballonets filled with air inside the envelope to regulate the changing gas-volume.
  • If the airship has a front and aft ballonet you can also steering the hight of an airship. For example, if you fill the aft ballonet with more air (leak some air out of the front ballonet), the airship will become heavier in the rear part of the envelope (air is heavier than helium), the ship gets an inclined position (nose up). In cause of the dynamic (from the engines), the airship will increase its altitude.
  • The airship can also be trimed through a front and aft ballonet.


 
Sectional elevation of the Parseval-Airship "PL VI", 1910
(red marked are the ballonets inside the envelope)
 
 
Elevator controling via front and aft ballonet, blimp (newer type)
(blue marked is the air/ballonet in the front and the aft section)



The advertising-blimps here in Germany today were build by the Westdeutsche Luftwerbung Luftschiffgesellschaft m.b.H. (WDL Luftschiffgesellschaft m.b.H.)  at Mülheim/Ruhr (near Essen). The WDL is building two different types of blimps. (Information about these types)
The ships are rented by companies (normally for one or two years) and will be painted with the comercial logo. At night there's the chance to make Night Sign - advertising. Therefor are about 10,000 coloured lamps attached to the envelope and controled by computer. (Only airship-type WDL 1b)