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Barrel & Chamber Ratios

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Barrel & Chamber Ratios

Unread postAuthor: silentfox_02 » Tue Oct 31, 2006 11:00 am

Hi I have not built a cannon and am going to start I am going for a 10' cannon and want to know whats a better & efficiant ratio :?:

7' Barrel and 3' Chamber

6' Barrel and 4' Chamber


any others?
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Unread postAuthor: joannaardway » Tue Oct 31, 2006 2:07 pm

It depends on your chamber and barrel diameters, and your fuel.

So: What ID (internal diameter) are you going to use for your chamber/barrel
And: what fuel are you going to use?

Oh yeah - don't ever use hairspray. It gunks up the chamber. Use a different spray instead (but not one that can damage the plastic), or propane.
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Unread postAuthor: silentfox_02 » Wed Nov 01, 2006 11:35 am

probably 2.5" barrel and 3" chamber I dont know what fuel but what I am asking is what should I use for C:B
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Unread postAuthor: joannaardway » Wed Nov 01, 2006 11:50 am

If you are using a spray can, then you'll need a chamber about 1.5 times the volume of your barrel.

If you are using metered propane, then having a chamber about .8 times the volume of your barrel is more efficent.

As this is a ratio, the common factor of pi can be expelled from both of the volume equations.
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Unread postAuthor: SpudBlaster15 » Wed Nov 01, 2006 6:51 pm

If you are talking about fixed chamber volume cannons, I wouldn't tie a specific ratio to aerosols in general. Obviously different sprays contain different chemicals which will have different energy densities, and will thus require different barrel lengths to harness all of the energy without creating the friction associated with the completion of combustion before the projectile has left the barrel.

With a fixed barrel launcher, a larger chamber will obviously give you higher levels of performance given any propellant, to a point.

When using aerosols, I find it best to make an overly long barrel, then cut it down until I get the desired performance level. I find that a 1:1 ratio works best on fixed chamber cannons using starting fluid.
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Unread postAuthor: silentfox_02 » Thu Nov 02, 2006 11:32 am

I guess I will go with 7' barrel and 3' chamber with diameters of 2.5" for spuds and tennis balls and 3" for the chamber only question is where do I get the pvc, like what store? will they let you buy if they know it is for a cannon?
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Unread postAuthor: reaper613 » Thu Nov 02, 2006 12:08 pm

i say do the 4' chamber, worst case you end up extending the barrel after you see how far your projectile goes and realize you can make it go farther. i mean the only thing better than a 10' cannon is an 11' right?
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Unread postAuthor: silentfox_02 » Fri Nov 03, 2006 2:51 pm

you mean 7' barrel and 4' chamber?


then where can I buy the pipe what kind of hardware store
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Unread postAuthor: SquishY » Fri Nov 03, 2006 2:59 pm

Try Lowes and Home Depot, I have the luxury of a really cheap plumbing supply house near me.
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