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Ratios

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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Ratios

Unread postAuthor: El Beasto » Tue Sep 11, 2007 3:29 pm

What is a good ratio to follow as far as barrel to chamber size goes? Length wise and diameter wise. Thanks!

Ratios on my gun:
Length-1:2
Width-1:3

Any problems?
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Unread postAuthor: DYI » Tue Sep 11, 2007 3:31 pm

These are useless, C:B ratios are always expressed as volume to volume. Diameter has very little effect in most cases.
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Unread postAuthor: CannonCreator » Tue Sep 11, 2007 5:52 pm

Here bro you need this. After you get your CB ratio off of this calc, you can ask this qustion

http://www.burntlatke.com/calc.html

Ude the link above, once your there select and download RatClac. It will give you more presice CB ratios, and it will show you the correct way to right it.
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Unread postAuthor: MrCrowley » Tue Sep 11, 2007 6:04 pm

CannonCreator isn't that calculator for combustions not pneumatics?

I hear there is no perfect ratio in a pneumatic but there is a good guide-line that it should be in, though I forogt what it is and can't find it.
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Unread postAuthor: DYI » Tue Sep 11, 2007 6:12 pm

Ratios for pneumatics depend on the pressure used. The higher the pressure, the larger the volume of the barrel should be for a given chamber size. At the pressures normally used, with a fixed chamber size, a .3:1 ratio can utilise most of the available power.
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Unread postAuthor: Rudesill Ballistics » Wed Sep 12, 2007 3:59 am

0.3:1 ratio?

So my "Kandy Kain" isn't as inefficient as I thought it was.
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Unread postAuthor: jimmy101 » Wed Sep 12, 2007 12:14 pm

DYI is a bit wrong since given the length to length ratio of the chamber and barrel, and the diameter ratios then volume ratios can be calculated. However, the normal way to express things is either as the volumes (or their ratio) or by giving the complete set of dimensions; length and width of both the chamber and barrel.

Of course, if you do it they way you did, you need to present the numbers in a manner that makes sense;
Ratios on my gun:
Length-1:2
Width-1:3

Does that mean the barrel is twice the length of the chamber and the diameter of the barrel is 3x the diameter of the chamber? Dosn't sound very likely.

Did you mean;
Code: Select all
               chamber : barrel
 length ratio        1  :  2
 diameter ratio    3  :  1

from which the volume ratio can be calulated as;
(volume chamber)/(volume barrel) = (pi)(r<sub>chamber</sub><sup>2</sup>)(L<sub>chamber</sub>) //(pi)(r<sub>barrel</sub><sup>2</sup>)(L<sub>barrel</sub>)

canceling things gives;
(r<sub>chamber</sub><sup>2</sup>)(L<sub>chamber</sub>) / (r<sub>barrel</sub><sup>2</sup>)(L<sub>barrel</sub>)

Using the ratios in place of the actual r's and L's;
(3<sup>2</sup>)(1)/(1<sup>2</sup>)(2) = 9/2 = 4.5


Now, like MrCrowley said, the optimal ratio of a pneumatic depends entirely on what you are trying to optimize. For optimal use of the available energy in the chamber then the barrel should be fairly long and the C:B fairly small, approaching roughly 1:9 (0.11 ratio) for a 120 PSIG chamber pressure.

For optimal muzzle velocity for a fixed barrel length, the chamber should be as large as possible. The ratio might be 3:1 (3 ratio) or more.
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