Re: Armored Airships Challenge

Steve Charlton wrote:

> Why not make it strong enough to hold a vacuum? 1/2 inch plate steel
> (with some internal bracing) would probably do. Aircraft machine guns
> wouldn't get through that. Use separate, sealable areas inside it,
> just in case you do get punctured by something. You'd get much greater
> lifting capacity than with helium or hydrogen.

The lifting capcity of vacuum isn't as much greater as you might think.

Air weighs around 1.2 kg/m^3 (all at sea level, 20 degrees C/70 degrees F).

Helium is about 0.17 kg/m^3, giving a lifting capacity of 1.03 kg/m^3.

Hydrogen is about 0.085 kg/m^3, giving a lifting capacity of 1.115 kg/m^3
(about an 8% improvement over helium).

Vacuum weighs roughly 0 kg/m^3 (depending on how hard your vacuum is), so
its lifting capacity is approximately 1.2 kg/m^3. That's only a 15%
improvement over helium and an 8% improvement over hydrogen (IOW, about the
same as switching from helium to hydrogen). But the increased structural
weight needed to deal with the pressure differential will almost certainly
wipe out that marginal gain in lifting power. You can certainly forget
about armor plating.

(I'm new here, but I think I've got my math right on this one. Be
embarassing to get it wrong, wouldn't it?)

--
Tom Schoene Replace "invalid" with "net" to e-mail
"Our country, right or wrong. When right, to be kept right, when
wrong to be put right." - Senator Carl Schurz, 1872




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