It's really not about improved performance, it's more about conserving
Helium for uses where it can be recycled. We have already had times in the
past where Helium has been in short supply.
On Thu, Jun 13, 2019 at 10:36 AM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Thu, 13 Jun 2019, DH Barr wrote:
All this hydrogen hullabaloo got me noodling: in atmosphere, what ratioof
gaseous hydrogen could be added to a helium gas envelope to improve lift
capability without appreciably increasing risk?
I would be surprised if it was enough to be very useful. Bear in mind
that the lift capability of helium is 25/29 the local air density, while
that of hydrogen is 27/29, so switching entirely to hydrogen gives only
about a 7% lift increase.
(Gas densities under normal conditions scale directly with molecular
weight. The average molecular weight of air is about 29, that of helium
is almost exactly 4, so a volume of helium weighs 4/29 the weight of the
same volume of air, and can lift 1-4/29 = 25/29 the weight of the air.
And likewise with hydrogen at a molecular weight of about 2.)
Mind you, as with rockets, given the various mass overheads, a 7% increase
in allowable "dry" mass can translate into a rather larger increase in
payload. But usually the key attractions of hydrogen are much lower cost
and no political constraints on availability; the extra lift is a useful
bonus but typically not a real decision driver.
Henry
