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How do i calculate a c:b ratio?

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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How do i calculate a c:b ratio?

Unread postAuthor: spudkilla » Sun Feb 11, 2007 6:00 pm

I am building a combustion cannon (hopefully fairly large 7-10 feet long)and I was wondering how long should the chamber be( 3 inch in diameter),and how long my barrel should be(1.5 inches in diameter)?I all ready searched, but i got nothing.
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Unread postAuthor: crazyfreak0075 » Sun Feb 11, 2007 6:09 pm

Im assuming u know how to use proportions but a .6-.8:1, C:B ratio is about right for a combustion cannon. Its all here in the wiki http://www.spudfiles.com/spud_wiki/inde ... rrel_ratio
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Unread postAuthor: SpudBlaster15 » Sun Feb 11, 2007 7:16 pm

What are you going to be using for fuel, and how are you going to get it into the chamber (Spray and pray, or a metering system)?

With that knowledge, we can give you an ideal ratio for your cannon.
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Unread postAuthor: spudkilla » Sun Feb 11, 2007 7:42 pm

Oh, i almost forgot..ill be using aerosol flammable fuels
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Unread postAuthor: spudkilla » Sun Feb 11, 2007 7:48 pm

Wait could i just double or triple or whatever the lengths on here to make it the size i want? http://www.spudtech.com/content.asp?id=5
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Unread postAuthor: willarddaniels » Sun Feb 11, 2007 9:55 pm

No, those are generic instructions. You should calculate the volume of both your chamber and the volume of your barrel, then use the ratios suggested by CrazyFreak. Typically, (.8-.95)Barrel:(1)Chamber

Start with your chamber. If it is 3" ID, and the length is 24", your volume would roughly be 168 cubic inches.
Your barrel should be 80-95% of that volume: 134-160 or 76-90 inches long, asssuming 1.5" ID barrel. That is a total length of 100-114 inches, not including space for a reducer.

Do not use these exact numbers for your gun, but use them as a template
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Unread postAuthor: SpudBlaster15 » Sun Feb 11, 2007 10:19 pm

spudkilla wrote:Oh, i almost forgot..ill be using aerosol flammable fuels


Use a C:B ratio of 1:1 if you are going to be using the 'spray and pray' method.

The formula for calculating the volume of a cylinder is as follows:

V=pir^2h
r = radius
h = height (or length)

You will want to use a chamber and barrel that have the same volume, so pick a chamber or barrel size, and calculate an appropriate component around it. You should beable to figure the rest out.
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