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Measurements for my combustion cannon.

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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Measurements for my combustion cannon.

Unread postAuthor: wangpushups » Sat Oct 27, 2007 4:59 pm

I have a chamber thats 4" X 14" sch 40 with (2) 90 degree elbos that has a volume of 3950 ml. and a 1.5" barrel. I have 10 feet of the 1.5 and i needed to know where to cut it for a perfect C:B. I could shorten the chamber to 12" if i need to so the barrel isnt too long. I also have a meter thats 1/2" X 10 with a volume of 70 ml. I realize that you guys get a lot of questions like this but i havent seen too many guys use a 4" chamber with a 1.5" barrel so i need to know how much psi goes into my chamber and i need a barrel measurement that will leave me with a .7:1 ratio.
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Unread postAuthor: DYI » Sat Oct 27, 2007 5:18 pm

The formula for volume of a cylinder is: PI x radius x radius x length= volume. Figure it out yourself.
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Unread postAuthor: wangpushups » Sat Oct 27, 2007 5:25 pm

The barrel needs to be shorter than 10 feet
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Unread postAuthor: dauphinoise potato » Sat Oct 27, 2007 5:35 pm

DYI wrote:The formula for volume of a cylinder is: PI x radius x radius x length= volume. Figure it out yourself.



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Unread postAuthor: wangpushups » Sat Oct 27, 2007 5:36 pm

I've already used the calculators and i have no idea how to use them so please dont post them or calculations like DYI just did.

I've spent about a 1 1/2 months building this dedicated cannon. I've spent about 1 1/2 weeks looking for measurements before i even made this post because you guys get so pissed at noobs for not knowing how to use the calculators n stuff and i realize that. I would really hate to throw this gun away just because i couldnt get help for the measurements on my gun. Please guys all i ask is for some help, i cant sleep until i get this thing done and post the pics. I know i would hate "spoonfeeding" too but i think that i could contribute a lot to this website once i get this done, like helping the newcomers with my diagrams.
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Unread postAuthor: DYI » Sat Oct 27, 2007 6:07 pm

Learn the math, this is stuff that you should learn in Grade 8. If you really are younger than 12, then you have my apologies, but you won't learn at all if we feed you all the numbers.

Just plug the measurement into the formula that I gave you to get the chamber volume. Divide the result by 0.7 to get the barrel volume that you need. Divide that by pi, and then by (radius of barrel^2) to get the barrel length that you need. Repeat for any chamber size until you get the desired result.
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Unread postAuthor: cwazy1 » Sat Oct 27, 2007 6:36 pm

with a 14" chamber. .

2x2x3.14x14= ur chamber volume
(too lazy to do conversions for ur elbows, do em ureslf then add to this number u get above)

with a 10' barrel

.75x.75x3.14x120= ur barrel volume

so with calculations, you get 175 inches cube for the chamber(not including elbows) and 211.95 inches cube for ur barrel.
to get the c:b ratio, divide the chamber number by the barrel number.

also keep in mind, if u have a cheanout, thats volume right there, same with any other fitting that is on ur 4" chamber pipe.
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Unread postAuthor: Novacastrian » Sat Oct 27, 2007 8:30 pm

Why not just do it the *easy way*? Attach long barrel and cut it down to perfection? A longer barrel usually works wonders anyway, it's hard to have a barrel thats too long :wink:
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Last edited by Novacastrian on Sat Oct 27, 2007 8:54 pm, edited 1 time in total.
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Unread postAuthor: DYI » Sat Oct 27, 2007 8:37 pm

Read this thread to see some good propane injection formulas. If you can figure these out, you'll have no trouble with the other stuff.
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Unread postAuthor: mark.f » Sun Oct 28, 2007 8:57 am

Start of by using a proportion of the form a/b=k, where a is one variable, b is another, and k is a constant.

In this context, k would equal your desired volumetric ratio, 0.7.

Now, you would add your terms to the equation. In this case simply your chamber volume over your expression for barrel volume.

<div align="center">Image</div>

Rearrange for l barrel length.

<div align="center">Image</div>

And then solve.



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