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End Of Week Plans

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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End Of Week Plans

Unread postAuthor: sprayandplay08 » Wed Jun 11, 2008 12:17 pm

This weekend i plan on building a over-under cannon using spray as a propellant.
I will be using 24" of 3" pipe with 60" of 1.5" pipe for a barrel and a
BBQ ignitor

What I would like from the community is suggestions or mods i can do to make it better? or any other advice u can give :lol:

i don't even know if it will work
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Unread postAuthor: MaxuS the 2nd » Wed Jun 11, 2008 12:24 pm

Use fully pressure rated components, I.E, no bell reducers.
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Unread postAuthor: sprayandplay08 » Wed Jun 11, 2008 12:25 pm

whats the difference?What should i use?
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Unread postAuthor: Maniac » Wed Jun 11, 2008 12:29 pm

Ahh sprayandplay just check the link in my signature. But DWV fittings(not pressure rated) ie: bellreducers are generally accepted when building combustions, dont worry yourself.
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Unread postAuthor: starman » Wed Jun 11, 2008 12:35 pm

Did you get your other one working yet?
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Unread postAuthor: sprayandplay08 » Wed Jun 11, 2008 12:36 pm

OK i will use pressure rated fittings


i'll be on tomorrow i have to leave for work

"Working at Krogers Sucks"
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Unread postAuthor: Canuck » Wed Jun 11, 2008 2:05 pm

Sounds like the one I just built only my cannon has a 16.5" long chamber and is "inline".
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Unread postAuthor: MrCrowley » Wed Jun 11, 2008 2:12 pm

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Unread postAuthor: Boom_erang » Wed Jun 11, 2008 4:49 pm

Looks to me like it would work OK, although you have more chamber than you really need. Your ratio with that chamber is 1.6:1, and thus you might get quite a bang out of it from the muzzle flash. Also, really long chambers aren't as efficient as shorter, fatter ones, IMO.

I'd suggest going with either something like a 12" to 14" x 3" chamber, personally. It will lighten the gun and give you plenty of power - it may even improve the performance a bit, although there are those that would argue with me about this!

For fuel, hairspray sucks, try Static Guard if you haven't already. No sticky gunk, and doesn't stink nearly as much.

-B
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Unread postAuthor: SpudFarm » Wed Jun 11, 2008 4:56 pm

NEVER EVER CUT OF THE CHAMBER TO GET RIGHT RATIO!
make the barrel longer and you get performance in truck loads :D
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Unread postAuthor: Boom_erang » Wed Jun 11, 2008 5:25 pm

So he's supposed to have a 95" barrel? I'm not sure how practical that is.

But I'm not convinced at all that reducing the chamber would not improve performance. Based on burntlake's tests, it seems that there is a ratio yielding max performance that stays fairly constant despite different gun sizes. Too long of a barrel for a given chamber reduces performance, and too short of a barrel reduces performance.

I know what you mean that for the max performance of a given chamber, you want the right length barrel. But the flip side of that is for a given barrel, you might get nearly the same performance from a smaller chamber if the ratio is better, and you'll save weight and fuel, because the gun is more efficient.

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Unread postAuthor: rcman50166 » Wed Jun 11, 2008 6:11 pm

This is true. My "Sarge" doesn't have a cut chamber and as a result it has an awkward look. The flame propagation isn't exactly amazing either. But if I had the chance to built another spray and pray, it would have a 6 in diameter chamber that is 18 in long. The barrel would be a 2.5 in dia. bore with a 36 in length. But I'm just dreaming, you build what you want. Just make sure you have a removable barrel so you can change the bore diameter. I forgot to do that on both my spray and prays.
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Unread postAuthor: Maniac » Wed Jun 11, 2008 10:33 pm

Hey Mr.C If you havent noticed I have put your identifying pressure rated pvc topic in my sig and I refrenced to it in my first post.
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Unread postAuthor: starman » Wed Jun 11, 2008 11:21 pm

All other things being equal, you will gain some power by going to a larger chamber and thus fuel mix, etc. However, unless you also lengthen the barrel or utilize a burst disk, much of that extra power will be going to waste and rushing out the end of the muzzle long after the projectile has cleared the barrel...and will represent itself as noise...more BOOM... :wink:

Do some HGDT calculations and just change the chamber size...you'll see the effect it has on it. You'll also see that unless you use a burst disk, you're not going to get a significant performance increase, maybe 10-15% is all if you go from a 3" chamber to a 4" chamber of the same length! ...barrel staying the same of course.
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