Larry Dighera wrote:
On Tue, 4 Mar 2008 14:47:54 -0800 (PST), Ricky
wrote in
:

hydrogen is a stronger lifting gas than helium.

The atmospheric displacement of hydrogen (H2 MW=2), with one fourth
the molecular weight of helium (He2 MW=8), should be a considerably
larger percentage of its mass.

Um, small correction: there is no He2 compound (well not normally).
So H2 MW=2, and He MW=4. Helium is twice as dense as H2 at the same
temperature and pressure.

That said, both gases provide nearly the same buoyancy - H2 provides all of
~8% more buoyancy that He. That is because buoyancy depends on the
differences of the densities, not their ratios. The densities at sea level
a

Air: ~1.29 kg/m^3
He: ~0.18 kg/m^3.
H2: ~0.09 kg/m^3
Vacuum: ~0.0 kg/m^3

Turns out a vacuum provides a little under ~8% more buoyancy than H2.

But because the hydrogen molecule is
physically smaller, containing it within the balloon envelope may be
an issue.

Well, both gases eventually leak through most LTA aircraft envelope
materials. (Metalclads like the ZMC-2 theoretically would fare best).

But the price of helium has done nothing but rise substantially for the
last few years. For some applications it has no substitute. Here's the USGS
site providing stats on worldwide production, consumption, estimated
reserves, and ever rising costs:

http://minerals.usgs.gov/minerals/pu...modity/helium/