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Re: Slow planes was: Battle blimps

From: Ryan M Gill <rmgill@m...>
Date: Fri, 19 Apr 2002 16:07:51 -0400
Subject: Re: Slow planes was: Battle blimps

At 3:34 PM -0400 4/19/02, Roger Books wrote:
>On 19-Apr-02 at 13:51, Allan Goodall (agoodall@att.net) wrote:
>>  On Fri, 19 Apr 2002 11:08:19 -0600, "B Lin" <lin@rxkinetix.com>
wrote:
>>
>>  > At 80,000-100,000 feet you could concieveably stand off from the
battle
>>  > area by 20-30 miles and still have a pretty good view (maybe not
in
>>  > mountainous areas, but still pretty good).
>>
>>  At 80,000 to 100,000 feet you run into some real problems with the
gas in
>>  the gas bag expanding. So the gas bag is going to be pretty darn
big. Look
>>  how big the gas bag for the "around-the-world" balloons were. It has
to be
>>  big to go up to those high altitudes. That was for a pressurized
sphere with
>>  a couple of guys in it. Imagine how big the bag is going to be for a
>>  zeppelin or blimp carrying enough weaponry to be useful.
>
>So why couldn't you pump it back into a storage container?

What makes the thing buoyant is that the volume of helium displaces 
enough of a volume of air that has a higher mass than the total craft 
weight. As you go higher, the air is more rarified and thus you need 
your Helium to expand to compensate for the lower mass. It does so 
rather nicely given that it may also expand.

However a rigid airship has an issue with the helium envelopes 
expanding beyond their ability to. The balloons do so by having a 
really huge envelope that is not entirely filled. Rigids tend to work 
with a smaller volume range on the gas envelopes. This requires a 
more confined altitude range.

Now, perhaps one could build a rigid or semi-rigid airship structure 
that has an expansion capability that retains a directional 
aerodynamic shape over the range of the expansion volume. Doing so 
would allow a greater pressure height.

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