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Anything wrong with a 2" chamber?

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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Unread postAuthor: hi » Thu Jul 05, 2007 4:34 pm

http://www.online-calculators.co.uk/vol ... volume.php

i saddly admit defeat :sign12:

although i still dont think it would work as well with a 4 foot barrel.
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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: Jumpin Jehosaphat » Thu Jul 05, 2007 5:29 pm

Now that I've had a little time to think about it, It's C:B ratio might be perfect, but I'm not sure what the optimum ratio for such a small chamber would be, not to mention friction which would have a disproportionately large impact here compared to other cannons. I would just go for it with the 4 foot long barrel and maybe cut it down if you don't like the performance.
I was wondering if anyone with a good combustion experience knew where the whole 0.8:1 came from in the first place, because the best C:B for combustions seems like it could vary based on chamber dimensions and such.
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Unread postAuthor: Binder17 » Thu Jul 05, 2007 6:44 pm

I think it was someone who built a spudgun on
Advanced spuds.com. He did several tests and came out with a chart showing the ratio to velocity.
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Unread postAuthor: Jumpin Jehosaphat » Thu Jul 05, 2007 7:03 pm

I wonder what the results would look like if similar tests were done using different chamber sizes, It could prove either that the optimum C:B is the same for all chamber sizes or not. If not using at least 3 (preferably more) different chamber sizes, you could create a formula where optimum barrel volume is represented as a function of chamber volume. People could make much better decisions about what barrel length to use and it would be an easy calculator to make.
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Unread postAuthor: boilingleadbath » Fri Jul 06, 2007 12:07 pm

...Jumpin, one of the Latke test launchers was actually pretty close to this size. (2" diameter, but a couple inches longer)

Indeed, Latke did do tests with 3 different setups... which tended to indicate that chamber size/shape doesn't have a whole lot to do with the optimum C:B ratio.

(as a note, EVBEC live is based mostly on the data from the test launcher most similar to the one this thread's original poster is building.)
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Unread postAuthor: jimmy101 » Fri Jul 06, 2007 12:54 pm

Binder17 wrote:So the .8:1 ratio I used is right and the specs I came out with are right?


Yep, your original specs are OK. HI is having a mathematical brain-fart, Jumpin Jehosaphat has the correct math, as did yoiu in your original post.

Pennies will spark but of course they would actually have to be in contact with (or very close to) the electrodes. Really shouldn't be any problem shaking the pennies back to the breach end of the gun before firing.

The gun would perform better with the same volume chamber made from larger ID pipe but the difference is fairly small and if you've got the parts laying arond for the 2" chamber gun then what the heck.
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Unread postAuthor: Jumpin Jehosaphat » Fri Jul 06, 2007 8:25 pm

boilingleadbath wrote:...Jumpin, one of the Latke test launchers was actually pretty close to this size. (2" diameter, but a couple inches longer)

Indeed, Latke did do tests with 3 different setups... which tended to indicate that chamber size/shape doesn't have a whole lot to do with the optimum C:B ratio.

(as a note, EVBEC live is based mostly on the data from the test launcher most similar to the one this thread's original poster is building.)


Hey that makes my life a lot easier for me. Thanks for letting me know this, I've learned a lot about spud guns this past month, but that is definitely one of the things I wasn't sure about. Thanks. :D
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Unread postAuthor: sandman » Fri Jul 06, 2007 8:45 pm

lol, in the first month that i was here with all the research that i did, i wrote a 5 page report on spudguns for school. It was the first time that i did not do the bare minimum for a report :lol:
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