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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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C:B Ratio.

Unread postAuthor: Extrusion » Mon Oct 09, 2006 9:24 pm

Well ive been working on a combustion that i call equinox and its going well ive added duel ignition (spark in front of chamber and back) and it increased performace ALOT so i luv it but theres something ive noticed when i shoot it i dont get the satisfieing BOOM! my others have made it makes more of the sound of a cork being popped like a vacum behind the projectile wich i think is do to the C:B Ratio i think the explosion has already reached its peak psi and starts cooling before the projectile is out of the barrel creating a suction behind the projectile therefore causeing it to sound like a popping cork rather then a nice BOOM! now i relize the a boom can mean wasted energy because the projectile has left the barrel before the explosion has reached its peak.

Confusing?

Anyway my C:B is .91:1 and i got the following quote from burntlatke "An efficient and powerful C:B ratio is 1.5:1." so should i shorten my barrel to get the 1.5:1 ratio or what i like boom and the cork sound is no fun.

Thanks for any help on this.
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Unread postAuthor: Benny » Tue Oct 10, 2006 4:43 am

Just keep shortening the barrel until u get the 1.5 to 1 cb ratio.
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Unread postAuthor: Extrusion » Tue Oct 10, 2006 11:27 am

Keep shortening or just shorten it to the 1.5:1 lol is the 1.5:1 a good ratio or should i stick with what i have now.
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Unread postAuthor: joannaardway » Tue Oct 10, 2006 12:59 pm

Stick with what you have now.

Loud Bang = inefficent.

If it makes lots of noise, you should extend the barrel. Inefficency isn't something you should deliberately seek.
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Unread postAuthor: Extrusion » Tue Oct 10, 2006 1:42 pm

But i like boom lol o well i could just make anotherone with like a 5in barrel that would be super loud lol.

i think i found out why it makes the noise my end cap was leaking pretty bad so i cleaned it up and now it sounds like a rifle lol
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Unread postAuthor: Karatedude13 » Tue Oct 17, 2006 7:37 pm

I've read the 1.5:1 ratio theory in plenty of places, so i'd stick to that. I'm doing my science fair project on it, so if anyone else has some stuff on it, let me know.
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Unread postAuthor: SpudBlaster15 » Wed Oct 18, 2006 11:54 pm

A 1.5:1 ratio is best in my experience. Any longer, and your ammo will stop accelerating before it reaches the end of the barrel, and the friction caused by the action of rubbing against the pipe's surface will slow it down immensely. Any shorter, and the highest pressure spike will occur after the ammo has left the barrel, wasting valuable energy.
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Unread postAuthor: 034936 » Sun Oct 22, 2006 8:45 pm

does this ratio go by length or volume?, the volume of chamber shud be 1.5 times larger than the barrel?
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Unread postAuthor: subterranean » Sun Oct 22, 2006 9:58 pm

yes the ratio is by volume formula for a cylinder is....
pi x (radius squared) x height=volume
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Unread postAuthor: SpudBlaster15 » Sun Oct 22, 2006 10:38 pm

After doing some tests, I have come to the conclusion that the 1.5:1 ratio does NOT give the best performance. It does however, give the best compromise between the satisfying BANG and extreme distance. Longer barrels give better distance, but are not as satisfying to shoot. Having interchangable barrels is an advantage in this case.
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Unread postAuthor: 034936 » Mon Oct 23, 2006 2:08 am

that sounds ok to me
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Unread postAuthor: patchystar04 » Mon Oct 23, 2006 7:34 pm

also i've found that using hairspray or glade you get that loud boom with just a kleenex in the barrel however with propane...i get this lame-o wooOOMMMM sound thats really dumb i like the boom so im trying to find a way to make CLEAN propane POP like hairspray Im thinging a burst of oxygen (like a tiny burst of it) however DON'T TRY THAT it may be catastrophic so idk idk ill find a way ( or someone else can help :D PS my cannon has the 1.5:1 ratio and its great but I NEED THE LOUD BOOM
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Unread postAuthor: Karatedude13 » Sat Nov 18, 2006 2:00 pm

I've also found that the 1.5:1 isn't the best for distance. A 1:1 was the best in my experiment. If you use Hairspray, you get the same loud BANG! no matter the ratio.
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Unread postAuthor: joannaardway » Sun Nov 19, 2006 12:16 pm

1:1 is in my opinion the best compromise - It goes Bang quite well, without too much power loss.

Personally, I prefer quieter cannons, because I live in a sub-urban area, so I keep my C:B ratios low for both combustions and pneumatics to avoid too much noise.

So, if building a combustion, I'd do it with a .7:1 to .8:1 ratio, and my Pneumatics tend to reside in the 1:1 to 1.5:1 ratio.
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Unread postAuthor: Tater Salad » Sun Nov 19, 2006 12:40 pm

what are you using for fuel now...? i have a large cannon with 1:1 ratio using propane and it leaves my ears ringing every time i shoot it. perhaps you should try a fan to mix the fuel so it all reacts.

And if anything i think you should using a coupling to expand the chamber so as not to compromise the length and accuracy of your barrel.
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