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Jun 09, 2011, 10:20 AM
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Take Off Weight

Bit of a trivial question, but since a blimp is neutrally buoyant would it's take off weight as classified by an aviation authority be 0kg? Or do they consider the take off weight as the mass?
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Jun 09, 2011, 01:08 PM
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The authorities are interested in what might fall on peoples heads. For models up to 150kg 'weight', at least in Germany, it counts what you could put on the scales. Without lifting gas. This is sometimes called 'weighable mass' or 'weight without gases'.

The German commuter airship requirements (LFLS) and the the transport airship requirements (TAR) are addressing a 'design equilibrium weight' in [kg]. This equals the weight of the air displaced by the nominal envelope volume (including Ballonets). So this would be comparable to 'displacement' for ships. What you would measure if you put your fully inflated airship on the scales is called 'static heaviness'. For the Zeppelin NT N07 this is about 5% of the nominal displacement.

'Take off weight' is then defined as equilibrium weight plus static heaviness.
Last edited by johannes.eissing; Jun 09, 2011 at 01:10 PM. Reason: definition of take off weight
Aug 20, 2018, 02:33 PM
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Now, 7 years later, 21b (2) LuftVO (the German air traffic regulation) states that the use of UAVs with a "start mass" of over 25 kg is forbidden. (Though the authorities can give exemptions.) Start mass sounds pretty unambiguous, so the situation for small unmanned airships seems much more restrictive today than what you described in 2011.

On the other other hand, 16 LuftVO used the term "total mass" (and not "weight") already in 1999 to define when permission is necessary for model aircraft. Since that was long before your post in 2011, maybe even "start mass" is not as unambiguous as it sounds, for the purposes of the LuftVO?

Of course, I am aware that type certification requirements (like LFLS) are a different story. Do you have any other info or sources that you can share? Or was it mostly goodwill towards small unmanned airships on behalf of the authorities, which wasn't/isn't necessarily codified?

PS: Not sure if this forum is still the best place for discussion, feel free to follow up elsewhere.

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