Re: Slow planes was: Battle blimps

At 9:18 AM -0500 4/19/02, Allan Goodall wrote:
>
>I know that there _was_ a ceiling. One of the problems zeppelins had
was that
>once they achieved a certain height they had to vent gas. The higher
you go,
>the less pressure on the gas. The gas would expand. If you let it
expand too
>much, the gas containment would rupture. So, they would vent gas.
Zeppelins
>would sometimes rise due to thermals, or other conditions (sunlight
could, I
>believe, heat up the gas and give the ship more lift). So, they then
had to
>vent gas to stop going too high and rupturing. Of course this meant
that when
>the conditions changed the ship would start to sink. They could pump in
more
>gas from containers, or they could dump ballast. Eventually they ran
out of
>gas and ballast and had to go home.

The more advanced Zeps had a special pressure valve that vented when 
the airship went above "pressure altitude". The American made 
Airships (The Akron and Macon) were fitted with condensors that 
recovered water vapor from the engines in order to replenish ballast 
and reduce the loss of ballast weight as fuel was consumed. Another 
benefit the US Zeps had was that since we were able to use helium, we 
could place the engines inside the skin (not the gas envelopes) and 
greatly reduce drag.

>I suppose a very high tech zeppelin could rise very high, but I'm not
sure
>what the operational limits are.

Depends on how it's fitted. The Helium balloons get to massively high 
altitudes. A Rigid or semi rigid Airship could get really high.
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