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Combustion AT4 (or similar)

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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Combustion AT4 (or similar)

Unread postAuthor: zephir » Sat Jan 19, 2008 4:25 am

I saw the completed pneumatic AT4, but wouldn't a combustion version of the same model be better? (more realistic)

If I decided build the combustion version (where I can get a simulated back blast) Would it still work if I had the chamber with the end open- like this?
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The construction is metal pipe, unless PVC works, A projectile, preferably something light and two sets of rings, one makes the front of the chamber, the rear makes up the back of the chamber. A plug could be inserted on the back nozzle to temporarily close the chamber up, for ignition. Then once both of the explosive gases are lit, the explosion blasts out both front and back, like a real AT4 (or similar rocket launcher)

If I use oxygen and propane, would I get that effect?

And whats the difference between the different gases- butane, propane, natural gas, and MAPP? Is there a significant difference in power between nthe gases?
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Unread postAuthor: jackssmirkingrevenge » Sat Jan 19, 2008 5:12 am

you'd want the chamber to be a bit bigger than that, and the rear opening should be quite narrow. Performance would be a little lacking though.
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Re: Combustion AT4 (or similar)

Unread postAuthor: Tsukiten » Sat Jan 19, 2008 5:25 am

I don't think you'll get very far with that sucky C:B ratio.
Anyway, cool idea :D
Some heavy recoil would be cool!
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Unread postAuthor: Carlman » Sun Jan 20, 2008 9:12 am

hang on a minute, you plug the end up with something that is not as tight a fit as the front projectile wouldnt all the energy just go out the back right after the paper wad?
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Unread postAuthor: psycix » Sun Jan 20, 2008 4:36 pm

You will definitely lose alot of power, depending on the size of the hole, and on the tightness of the back sealer.

You could make two separate chambers (or maybe with a very small hole between) wich ignite at the same time. (dual spark gap, in each chamber one)


About your question about the fuel:
There is not much power difference between those fuels, usually there isnt a notable difference. Adding a chamber fan or having a good C:B ratio is way more important then the choice of fuel.
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Unread postAuthor: Carlman » Sun Jan 20, 2008 6:00 pm

psycix wrote:You could make two separate chambers (or maybe with a very small hole between) wich ignite at the same time. (dual spark gap, in each chamber one)


that was EXACTLY what i was going to post lol, oh well i second the duel chambers :D
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Unread postAuthor: Skywalker » Sun Jan 20, 2008 6:07 pm

Yeah, I noticed a pretty sizeable power decrease when firing my combustion gun w/ a 3/8" or so hole in the chamber wall (took my lantern sparker out and held a match to the hole -- almost burnt my fingers too!) Your plug would help somewhat, I'm not sure how much.
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Unread postAuthor: ALIHISGREAT » Sun Jan 20, 2008 6:33 pm

you should use a small barrel if you are doint a design like that so you get more power, and the two chambers are a good idea.
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Re: Combustion AT4 (or similar)

Unread postAuthor: Ragnarok » Sun Jan 20, 2008 7:29 pm

zephir wrote:I saw the completed pneumatic AT4, but wouldn't a combustion version of the same model be better? (more realistic)

Although I admire your innovation, in real life such things use many ounces of propellant, and they actually gain most of their speed after the "muzzle", so they can afford to lose some power to reduce the otherwise very large recoil.

Combustion is a matter of a gram or two of gas. (About 1.2 - 1.3 grams a litre), and there isn't much recoil to worry about in the first place. I have seldom seen a (handheld) potato cannon that risks injuring it's user with recoil. The smaller energy available means that there is none to spare for gimmicks like this, especially as you'd get very little in the way of back blast. You might get a propane blue flash out the back if you did it at night, but the recoil reduction would be from the severe loss of power, not the back blast.

Not to mention that if you do that you have to worry not only about projectiles to the front, but a risk of injury to people behind, which means there is no safe place (to the sides is not considered safe in my book).
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: zephir » Fri Jan 25, 2008 5:20 am

Ragnarok wrote:Although I admire your innovation

Thank you

Ragnarok wrote:severe loss of power

Ya, I know. many recoil-less rifles have the same problem. those are a cross between a rifle and a bazooka. Half the gas pushes something forward, half the gas out the back.
Except this time the gas out the back creates the backblast. RPGs and MAWs blackblasts can be hazardous to people behind it up to 50 meters.
If theres a problem with power, why not put more gas in? The backblast will be more noticable, but not hazardous or dangerous. Also, is there a type of gas that gets more of a yellow flame than a blue one?

Its really for show, not practical purpose. If its for practical purpose, I would post on a different site. That way I wouldn't break any rules regarding banned projectiles.
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My interest on spud guns began when I couldn't legally buy guns.
Now its because my guns are too loud to legally shoot.

Its not like it was legal to being with, but they don't offer subsonic 7.62x39 or 7.62x54R. They only have subsonic .22 long. Thats no fun stuff doesn't explode.

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