Chamber size question

Boom! The classic potato gun harnesses the combustion of flammable vapor.
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Brooner115
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How big of a chamber would I have to have to support a 60" long 1 1/2" barrel??

I only have 3" pipe so if you could tell me how long of 3" pipe I would need that would be great :) .

I'm thinking I need around 18"s to get the best performance out of it but I'm not sure could someone pleaze help?? I'm a complete retard when it comes to c:b ratios and good performance. oh ya its a combustion cannon.
Last edited by Brooner115 on Sat Apr 28, 2007 11:03 am, edited 1 time in total.
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super spuder
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um. is it pneumatic or combustion?
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Brooner115
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damn it!! I knew I forgot something its a combustion sorry about that. :roll:
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hi
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you will have to have it be about 2 1/2 feet long.
"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Velocity
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The optimal chamber to barrel ratio for a propane powered combustion is 0.8:1.

Your barrel is 1.5" x 60"; the volume is therefore about 34pi

You need a chamber with a volume 80% of that, or 27.2pi

Divide 27.2 by 2.25 (which is (3/2)^2), and you get about 12

Your combustion chamber needs to be about 12" in length
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hi
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rmich, there is no way thats right, a 12'' chamber will be way to small. A 12'' chamber is good for about a 35'' barrel, not a 60''.
"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Velocity
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Well...
Barrel: ((1.5/2)^2)(60)(pi) = 33.75 pi cubic inches
Chamber: ((3/2)^2)(12)(pi) = 27 pi cubic inches

This creates a chamber to barrel ratio of 0.8:1

hi, keep in mind that each inch of 3" pipe has 4x the volume of each inch of 1.5" pipe... and the calculations don't lie.
Last edited by Velocity on Sat Apr 28, 2007 1:32 pm, edited 1 time in total.
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SpudBlaster15
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Last edited by SpudBlaster15 on Wed Jul 14, 2021 3:27 pm, edited 1 time in total.
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Brooner115
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Ya guys its gonna be a hairspray combustion and thanx to all of you for helping me out I think i'm gonna go with a 18"-20" chamber in between what all of you where arguing about thanx a bunch :P :P

Whats OP mean? is that a complement or a nickname or are you making fun of me? lol :lol:
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SpudBlaster15
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Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras nec placerat erat. Vivamus dapibus egestas nunc, at eleifend neque. Suspendisse potenti. Sed dictum lacus eu nisl pretium vehicula. Ut faucibus hendrerit nisi. Integer ultricies orci eu ultrices malesuada. Fusce id mauris risus. Suspendisse finibus ligula et nisl rutrum efficitur. Vestibulum posuere erat pellentesque ornare venenatis. Integer commodo fermentum tortor in pharetra. Proin scelerisque consectetur posuere. Vestibulum molestie augue ac nibh feugiat scelerisque. Sed aliquet a nunc in mattis.
Last edited by SpudBlaster15 on Wed Jul 14, 2021 3:26 pm, edited 1 time in total.
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boilingleadbath
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One note:
The discussion that has occured up to this point gives you the smallest chamber that can keep the spud from slowing down before it leaves the barrel - not the chamber that will give you the most muzzle energy.

To maximize muzzle energy with a fixed barrel length, you generally want a chamber bigger than their calculations suggest.
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