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3 foot by 4 inch chamber 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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3 foot by 4 inch chamber question

Unread postAuthor: Blackspire » Tue Sep 19, 2006 8:44 pm

In the process of building a new potato gun, with a 3 foot by 4 inch chamber, and a 5 foot by 2 inch barrel. I don't want to hear all the "correct" ratio's as the deed is done and I don't want to hear about the screw up's I made! :oops: . I am just wondering where would be the best place to put the sparker? Towards the back, front, or right in the middle like most guns?
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Unread postAuthor: POS » Wed Sep 20, 2006 2:18 am

If I was you, I would place multiple sparkers. At least 1 every foot.

If you use just 1, I would place it somewhere in the midle, or near the barrel.

If you put it way back, the burning gas will "shoot" away non-ignited gas, befor it gets the chance to burn I guess.
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Unread postAuthor: Blackspire » Wed Sep 20, 2006 7:58 am

I put it closer to the barrel(but still somewhat near the middle, if that makes sense). My thinking was that it is going to take some ether to fill the whole chamber, and I don't want to "flood" the sparker so I put it closer to the front. If it doesn't work I can still put another one at the back.
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Unread postAuthor: sgort87 » Thu Sep 21, 2006 11:41 am

Actually, you guys are wrong.

The multiple sparks method does work best, but if one spark is going to be used, the best place for it is about 2/3 to 3/4 of the way back.

The reason for this is that it creates a jet of flame that shoots out toward the barrel and the flame then spreads to the outside areas. If the spark is in the front, the flame slowly reaches the back because the expansion is just moving the flame farther from the rest of the gasses.

If you don't believe me, you can go on Spudtech and ask. It's a tried and true fact.
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Unread postAuthor: Blackspire » Fri Sep 22, 2006 12:31 am

Damnit! I should have just stuck it in the middle. Well I guess I will test it out tomorrow, and if it's just not working like it should, I will have to add another sparker.
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Unread postAuthor: MrCrowley » Fri Sep 22, 2006 12:45 am

well its not going to hinder performance that much, just put a 4" sleeve over the holes and put the sparker in the middle.
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Unread postAuthor: cannon freak » Fri Sep 22, 2006 4:07 pm

One spark is perfectly fine, I have a dual chambered cannon with 4" by 3' chambers and one spark each works just fine.
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Unread postAuthor: Blackspire » Sat Sep 23, 2006 9:42 am

MrCrowley wrote:well its not going to hinder performance that much, just put a 4" sleeve over the holes and put the sparker in the middle.
No way to get a sleeve on there now. I could probably figure a way to patch it, just have to make sure it's not going to come off. The other thing is getting the sparker out might be interesting. Hmm.
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Unread postAuthor: Blackspire » Sat Sep 23, 2006 9:43 am

cannon freak wrote:One spark is perfectly fine, I have a dual chambered cannon with 4" by 3' chambers and one spark each works just fine.
Holy crap. :shock: My one chamber looks massive, two of them would be crasy.
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Unread postAuthor: pyrogeek » Sat Dec 02, 2006 7:58 pm

How big of holes did you make that you need to patch? Maybe you could use them for something else. Or maybe cut the 4inch sleeve lengthwise and then mount something like a sight on it, claiming it was all in the original plan.

You could probably cut that chamber down, and make another cannon out of what you removed. Sorry if you take offense to that and didn't want to hear it, but just consider it.
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