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speed of sound

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: Boomer_ » Tue Sep 19, 2006 7:02 pm

i have a 20 pound co2 tank, i could make a metal gb gun (metaphorically) could i reach the speed of sound if i were to make the world's most efficient piston valve too?(matephorically)
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Unread postAuthor: boilingleadbath » Wed Sep 20, 2006 4:06 pm

Go try it with the GGDT... because I'm not going to do it for you.
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Unread postAuthor: Jolly Roger » Thu Sep 21, 2006 8:21 am

How accurate is GGDT? Its just that I've discovered alot of things in it that just don't add up... Such as when you put really high pressures into it, the velocity goes up and down up and down and all over the place. The projectile diameter can be bigger than the barrel? WTF? Cartoon physics there... It actually improves perfomance according to the program. I won't go on but another one is that the Outside diameter is actually the inside diameter?? And the optimization thingo is completely "in need of reveiw", I put in a fixed total length for a cannon and the results came back at well below one quarter the performance it was already set at. Yeah theres a few more things but what I'm saying is that I wouldn't use the program as gospel thats all.
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Unread postAuthor: boilingleadbath » Thu Sep 21, 2006 4:38 pm

The optimization algorithm <i>is</i> buggy. Has nothing to do with anything else in the program, though...

The really high pressure phenomenom is due to using a time interval of one 10,000th of a second (or something like that). At really high pressures, enough can happen between 'frames' that it acts funny. My bet is that you won't notice it with most cannons, considering that that it spends a few hundred frames calculating their preformance.

Yeah, the projectile diameter can be bigger than the barrel. I *think* this is to allow modeling of interesting situations, but I'm not sure... it might just be that D Halls was too lazy to put in an idiot protection system. (which <i>are</i> annoying to implement)

...and it ends up being within several percent. No substitute for actual velocity measurements if you want to hit small children at 200 yards, but most of us arn't trying to do that (nor are our barrels accurate enough...).
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Unread postAuthor: zeigs spud » Tue Sep 26, 2006 4:30 pm

jrrdw wrote:What i would like to have is very quite and very fast, i want mine so quite you can bearly hear it sitting rite beside it! Flat shooting for at least 250 yrds. Now that is my ideal cannon.


i sugest a large pressure chamber and a VERY large silencer. you can search silencers and find a thread on how to make them. All they are is a peice of pvc a lil bigger that the barrel with holes drilled in it then a "cushion" or air muffler (examples, clothlike things,carpet,ect.) on top. After that you fit anotherlarger peice of pvc on top woth holes drilled in it too. a silencer will probably not do completely wht you want for the gun your imagening but will drasticly help it you make it right.
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