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C:B ratio

A place to ask general spud cannon related questions.
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C:B ratio

Unread postAuthor: patatoSteve » Sat Nov 11, 2006 12:21 am

I dont understand C:B ratio. I read about it on on SpudWiki ,but dont undersnd how 0.6-0.8:1 translates to achamber with a length of 1 foot and a barral the length of five feet. Can somebody tell me how this works.
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Unread postAuthor: SquishY » Sat Nov 11, 2006 12:30 am

The chamber is a larger diameter, ie. 3x12" chamber and 1.5x60" barrel(not exact, I pulled these numbers out my ass) but do you understand now?
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Unread postAuthor: iamthewalrus » Sat Nov 11, 2006 1:06 am

C:B is the ratio between the volume of the chamber and barrel, not the length. so if the chamber is say 80cc, then u want ur barrel to be 100cc. and the volume is based on diameter to length. so i think if the chamber and barrel are the same diameter then the barrel needs to be 20% longer then the chamber.
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Unread postAuthor: patatoSteve » Sat Nov 11, 2006 1:16 am

Thanks I get it now. :D
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Unread postAuthor: experament_u2 » Sat Nov 11, 2006 1:30 am

i never rely did understand C:B ratio and still dont can u explain it a bit easyer plz fora ll us downers
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Unread postAuthor: iamthewalrus » Sat Nov 11, 2006 1:42 am

ok C:B is the ratio between the volume of the chamber of the gun and the volume of the barrel. say you chamber is 50cc and ur barrel is 100cc, that means the C:B of ur gun is 50:100 or 1:2 . do u understand a bit now?
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Unread postAuthor: POS » Sun Nov 12, 2006 3:20 pm

The chamber should be bigger than the barrel for better performance
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Unread postAuthor: Hayseed_Andrew » Sun Nov 12, 2006 3:39 pm

What if you wanted your gun to be quieter, or is that even a resonable desire? Is it possible to "silence" a a gun so that it can hardly be heard from around 100' away?
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Unread postAuthor: POS » Sun Nov 12, 2006 4:27 pm

it's possible.... with a very big silencer.
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Unread postAuthor: iamthewalrus » Sun Nov 12, 2006 4:30 pm

POS, the best C:B ratio for propane is .8:1, burntlake proved that, if u talking about anything other then propane idk. but for propane bigger chamber is not better.
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Unread postAuthor: SpudBlaster15 » Sun Nov 12, 2006 8:08 pm

For a FIXED BARREL launcher, a bigger chamber is better, to a point. For a FIXED CHAMBER launcher, the ideal ratio for best efficiency (per moles of propane to muzzle energy) is 0.8:1. If you want maximum velocity, you will want an even longer barrel. Because velocity is not directly proportional to muzzle energy, rather the square root of muzzle energy, the ratio is changed up a bit, and ends up being closer to 0.6 - 0.7:1.

When using aerosols, you usually end up with an imperfect fuel mix, and less available energy as a result. A fixed chamber aerosol launcher using a decent fuel like right guard or starting fluid would strike a balance between consistancy and power at around 1:1. Hairspray launchers usually need an even larger chamber/shorter barrel.
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Unread postAuthor: drac » Sun Nov 12, 2006 8:23 pm

Spudblaster, I would like to know how you got those figures. I'm intrigued.
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Unread postAuthor: iamthewalrus » Sun Nov 12, 2006 8:25 pm

and i would like to know wtf a fixed chamber and a fixed barrel cannon are, or how they differ.
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Unread postAuthor: SpudBlaster15 » Sun Nov 12, 2006 8:32 pm

iamthewalrus wrote:and i would like to know wtf a fixed chamber and a fixed barrel cannon are, or how they differ.


They are just as they sound. If you are going to be optimizing a barrel for a certain chamber size, this is fixed chamber. If you are going to be optimizing a chamber for a certain barrel size, this is fixed barrel.
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Unread postAuthor: SpudBlaster15 » Sun Nov 12, 2006 8:35 pm

drac wrote:Spudblaster, I would like to know how you got those figures. I'm intrigued.


Somebody on Spudtech did a whole bunch of calculations that proved this to be true, I am just restating what they calculated as I am far too lazy to do the calculations myself. I will try to dig up the thread for you, although it is probabaly buried now.
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