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From: msb@lsuc.UUCP (Mark Brader)
Newsgroups: net.misc,net.physics
Subject: Re: Hydrogen
Message-ID: <573@lsuc.UUCP>
Date: Wed, 3-Apr-85 04:41:42 EST
Article-I.D.: lsuc.573
Posted: Wed Apr  3 04:41:42 1985
Date-Received: Wed, 3-Apr-85 06:01:09 EST
References: <708@mhuxt.UUCP> <643@houxa.UUCP> <359@mnetor.UUCP> <1211@reed.UUCP>
Reply-To: msb@lsuc.UUCP (Mark Brader)
Organization: Law Society of Upper Canada, Toronto
Lines: 20
Summary: Hydrogen isn't twice as buoyant as helium

> There is one big advantage of hydrogen over helium:  hydrogen
> has a much greater "lifting power", four times as much according
> to a book _Airships_ I read a long, long time ago. Four times
> strikes me as off, since hydrogen, though of atomic weight 1.00X,
> is diatomic.  Thus it would only have "twice" the lifting power.

No, what it would have twice is the density.  The buoyancy is proportional
to the difference between the density of the gas and the density of air.
As I calculated in another article, the average molecular weight of air is
29.1; hydrogen is 2.0 and helium is 4.0.  And the density of a gas is
in direct proportion to the molecular weight.  So hydrogen is nowhere near
twice as buoyant as helium, but only 27.1/25.1 = about 1.08 times.

This is still enough to be significant in airship contexts, though.

(Another disadvantage of helium is that its tiny atoms leak through materials
that won't pass other gases.  I don't know how bad hydrogen is this way,
though, or how significant this effect is.)

Mark Brader