🚀 go-pugleaf

01crmeyer@leo.bsuvc.bsu.edu (Craig Meyer) writes:
>I'm looking into the concept of running an automobile off of compressed air.
>According to my calculations (based on a Gast airmotor catalogue), such a 
>vehicle would need air tanks that could hold 100,000 psi.
>Is that at all possible?

I'll take a shot at this for fun, but be aware that I am *not* a
materials person.  The short answer is no, it isn't possible. Or rather, 
yes it is but it isn't a good way to make a speedy automobile.  (This is 
of course my ignorant opinion--I could be wrong.)

From my scuba diving days we know that a steel cylinder will hold about 
2500 psi, and such a cylinder weighs in at about 20 lbs (there ought to be 
some more current divers who can give us the exact weight of a tank).  Now 
you want to put in 100,000 psi, a factor of 40 increase in pressure.  It 
seems reasonable that a factor 40 increase in the wall thickness is needed 
to compensate.  The weight of the tank, however, will go roughly as wall 
thickness squared (mass = density*pi*(r_outer^2-r_inner^2)*height), so now 
we're talking a 40*40*(20 lbs) = 3200 lb tank.  This sucker will also be big; 
tank walls in scuba are at least an inch thick if memory serves and 
we're going to increase that by 40. This gives us a tank about seven feet 
in diameter at a bare minimum.

Now all this assumes that we're scaling up a scuba tank to fit your
application.  There may be better designs (spheres maybe) that will
make 100,000 psi practical.  I'm sure there are high pressure
experimentalist types out there who can give a real answer.

Doug Miller	doug@retzlaff.llnl.gov
"But *why* can't I use a gas station air pump on my bike tire?"