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Chamber size question

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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Chamber size question

Unread postAuthor: Brooner115 » Sat Apr 28, 2007 10:53 am

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.
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Last edited by Brooner115 on Sat Apr 28, 2007 11:03 am, edited 1 time in total.

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Unread postAuthor: super spuder » Sat Apr 28, 2007 10:58 am

um. is it pneumatic or combustion?
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Unread postAuthor: Brooner115 » Sat Apr 28, 2007 11:03 am

damn it!! I knew I forgot something its a combustion sorry about that. :roll:
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Unread postAuthor: hi » Sat Apr 28, 2007 11:07 am

you will have to have it be about 2 1/2 feet long.
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Unread postAuthor: Velocity » Sat Apr 28, 2007 11:36 am

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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Unread postAuthor: hi » Sat Apr 28, 2007 12:31 pm

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''.
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"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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Unread postAuthor: Velocity » Sat Apr 28, 2007 1:31 pm

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.
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Last edited by Velocity on Sat Apr 28, 2007 1:32 pm, edited 1 time in total.
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Unread postAuthor: SpudBlaster15 » Sat Apr 28, 2007 1:32 pm

Rmich would be correct, if the inside diameter of 1.5" pipe was actually 1.5". With it being closer to 1.6", the optimal chamber length is ~14".

(Keep in mind we are discussing metered propane cannons, and the most efficient C:B ratio.)

However, I have a feeling that the OP is going to be using aerosol fuel in his cannon, in which case, a good chamber length would be 17 - 18".
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Unread postAuthor: Brooner115 » Sat Apr 28, 2007 4:42 pm

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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Unread postAuthor: SpudBlaster15 » Sat Apr 28, 2007 4:58 pm

OP means original poster.
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Unread postAuthor: boilingleadbath » Sat Apr 28, 2007 10:48 pm

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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