Do ballonets control the buoyancy of a Zeppelin NT?
The NT, being semi rigid, does not work like a balloon where buoyancy of the airship is controlled by adding or releasing helium. The quantity of helium carried is set at the beginning of the flight, and is set so that the aircraft is heavier than air. Vertical motion is then controlled by engine power. Buoyancy control is not the ballonet's purpose.

Ballonets are used to maintain constant pressure in the hull, as this is required for structural integrity. Whatever additional volume is required beyond that consumed by the helium carried is filled by air pumped into the ballonets. This air may also be released to control pressure as the craft ascends, and pumped back in as the craft descends. The hull is not designed to be pressurized beyond 5mbar.

Zeppelin GMBH technology


  Envelope - Non-flammable Helium, contained in a high strength, multi-layered laminate, provides the necessary lift. The envelope pressure is maintained at only 5mbar above atmospheric. Air chambers, the so-called “Ballonets” help to keep a constant interior pressure at all flight altitudes, and maintain a rigid hull.