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A place to ask general spud cannon related questions.
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Unread postAuthor: frogy » Mon Jun 26, 2006 10:52 pm

The one that Joel used to break the sound barrier only has 1 large chamber...

<img src="http://spudtech.com/images/products/UOkcannonfull.jpg">

Not humongeous (sp?), but I believe Joel, and with a Supah valve I bet it did...
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Unread postAuthor: boilingleadbath » Mon Jun 26, 2006 11:08 pm

1000 f/s isn't the speed of sound in air at any temperature you should be launching potatoes in. Rough estimations predict that it'd have that speed at about -50*C... that's -60*F!

For achiving supersonic velocities with projectiles of any significant mass, a 15' barrel isn't that big for that pressure.

As to 'easily', have you acctualy bothered to model it using the GGDT? He only has 2/3 of the required energy to get supersonic speeds with a 150g potato using:
8' of 6" as a chamber
15' of 2" as a barrel
a 2" ported burstdisk with 70% flow (compare that to a supah!)
hydrogen at 120 psi

Yes, if he where to reduce the mass to 80g or so, it's possible. Which is a reasanable mass for a potato in 2", admittedly, if a bit less than expected.

Of course, that's not the launcher he claims got supersonic velocities.
That particular launcher looks like a 4"x60" chamber and a 2" x 10' barrel.
Using the burstdisk, gas, and pressure I used last time, it requires reducing the potato slice to less than 1" thick (50g) to get supersonic velocities.

On the other hand, the remaining hydrogen in the barrel will quickly be expelled in a manner similar to the blast from a combustion. It can move faster than the speed of sound in air, so you'll get a VERY loud 'bang' compareable to an insanely large 2x hybrid.
I can't blame him for being confused.

As to benstern, he's being silly.
He has clearly forgotten the current market price of aerogels.
A chunk of foam is one's best [affordable] bet. The pink insulation stuff is roughly 30 mg/cm^3.
Admittedly, it means that a 2" projectile 1" thick would weigh 2g or so, but at least it doesn't cost 200+ $ per chunk of material, nevermind the issues in obtaining a lump of aerogel that big.
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Unread postAuthor: benstern » Mon Jun 26, 2006 11:27 pm

wait were you talking about my launcher?
(punches in 70% for burst disc>
billard ball with a 20' long 2.5" SCH-80 barrel - 1699 feet per second
golfball with 20" long SDR GB barrel - 2382 feet per second
It is better than i could ever hope for!

EDIT: golfball is mach 2.04838!!!!!!!
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