Jaqua wrote:

However, for your car the concept of a compressor
hooked to the gas tap, and topping up the car every night
with low  cost - no road tax fuel is rather attractive, and would beat
a ton of lead acid batteries by a whole  bunch - Vance

Heck Vance! Anything would beat lead acid batteries including rubber bands :-)

But I like that municipal gas supply idea. Any plan to deny the gov
tax money is a good plan. P&W compresses municipal gas supplies real time to
run their power generating gas turbines in the Hartford Conn. high altitude test cell
facility. Would my 3 HP Sears air compressor work? How about a filament wound
composite storage tank to save weight? I am also curious about how weight
efficient a bunch of long thin wall aluminum tubes would be as a storage tank.

Paul Lamar

I am afraid that your Sears compressor lacks the muscle, but it realy does not require a
very sophisticaated compressor - just high pr output, and leak free. The surplus strut
compressors that used to be available before the SCUBA crews bought them all up would be
great. I think the safety issues are over sold by the
lawyers and politicians. In a well ventilated area it would be safer than propane since it
is lighter than air. Tubes are not a bad second choice to spheres, but everything is heavy.
If you used 60ksi aluminun downgraded to 30ksi (much more aggresive than ICC safety
factors) at 3000 psi the wall thickness should be 1/10th
the radius, and you would need about 3 pounds of tank for each pound of fuel.

However if you got "T-boned" in the tank, it would make a Pinto look like a pilot light.

And yes, if you are a conscientous law abiding citezen you should volunteer :-) to pay the
road tax. - Vance

A 1/4 inch wall 5 inch diameter tube sounds very conservative. 6061T6 ought to be better
than that. If you get a crack it would not fail the tube catastrophically 
(hand grenade mode) or would it? Seems to me there is not enough volume of 
gas in there to release all that great amount of mechanical energy. Metal
elongation at ultimate stress I guess has something to do with it. 

What is the formula that gives wall thickness as a function of pressure, allowable 
stress and radius?

Would welding on the end caps be a big reliability problem.
Except for the weight penalty over a sphere sounds like a practical way to make 
a home made tank of almost any form factor. I see a lot of compressed gas trucks
running around with these kinds of tanks.

Paul Lamar
 
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