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Loss of power

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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Loss of power

Unread postAuthor: Kaotik Kustoms » Tue Jan 15, 2008 7:09 pm

I just built my first cannon (a small one) It has a 3" dia chamber by 12" long and it reduces down to 1.5" I'm using dentured alchol in a spray bottle as my fuel and a grill sparker and my ignition source. My question is why doesnt my have nearly as much power as vids i have seen? I tried shooting a paper ball that fir the barrel nicely and it doesnt even have the balls to shoot that. Any suggestions?
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Unread postAuthor: LikimysCrotchus5 » Tue Jan 15, 2008 7:12 pm

Well first of all, because paper is light, it will go no where, no matter the power.

Second, you need to use a better fuel to air ratio. If you experiment, you will find the right mix.

Third, you can use a different or better fuel, like propane, or Axe.
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Unread postAuthor: DYI » Tue Jan 15, 2008 7:21 pm

As long as you use properly metered propane in combination with a fan and a C:B ratio of ~0.8:1, power will be decent by most spudgun standards.

If you have no method of precisely metering fuel and creating turbulence in the chamber to speed the flamefront, performance will be wildly variable, and, in general, roughly equal to (f*ck all / 2).

Pneumatics are far simpler than combustions, and are a good place to start for the beginner. Combustions are rather complex pieces of equipment in comparison, and require some skill to build properly, which, by the fact that you're expecting to get decent performance out of something with such a poor drag coefficient and sectional density as a ball of paper, you likely don't have.
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Unread postAuthor: Kaotik Kustoms » Tue Jan 15, 2008 7:22 pm

Well i don't have anything to shoot so i figured i would try a wad of paper just to see if all the components were working. Anybody know of a good starter ratio? Will i get more preofrmance running it more rich or lean?
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Unread postAuthor: ralphd » Tue Jan 15, 2008 7:28 pm

I agree. I found that the Suave deodorant in the blue can works great. Aqua net is the best but it leaves a sticky mess. I once used rags to do testing but potatos are much better.
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Unread postAuthor: LikimysCrotchus5 » Tue Jan 15, 2008 7:54 pm

ralphd wrote:potatos are much better

Hence the name "spud gun" or "potato cannon" :wink:

I agree with DYI, pneumatics are much simpler, depending on what you are trying to do, but generally are easy. There is not much to go wrong with. They are reliable and powerful as well. The only con is that they are not as portable, but there are ways to fix that.

A simple pneumatic has 3 components:
Chamber
Valve
Barrel

Depending on what performance you want, the sizes of chambers and barrels, and the different sizes and kinds of valves can give better/worse performance.

DYI wrote:creating turbulence in the chamber to speed the flamefront
By this statement, do you suggest leaving the fan on when firing the combustion cannon?

DYI wrote:f*ck all / 2

you have ne more ratios that you might like to explain :)
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Unread postAuthor: Fnord » Tue Jan 15, 2008 9:08 pm

Something that not many people realize...

Paper, cloth, and really anything that burns easily is horrible to use in a cannon because it will throw your fuel/air ratios off.
If the paper ignites in the barrel even partially, it consumes oxygen that the fuel would normally use, thus resulting in incomplete combustion.

And you get smoke in the chamber. Cool effect when venting, but annoying if you want performance.
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Unread postAuthor: Eddbot » Tue Jan 15, 2008 9:23 pm

i just noticed that DYI is very good at hiding insults in his posts
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Unread postAuthor: Kaotik Kustoms » Tue Jan 15, 2008 9:24 pm

_Fnord wrote:Something that not many people realize...

Paper, cloth, and really anything that burns easily is horrible to use in a cannon because it will throw your fuel/air ratios off.
If the paper ignites in the barrel even partially, it consumes oxygen that the fuel would normally use, thus resulting in incomplete combustion.

And you get smoke in the chamber. Cool effect when venting, but annoying if you want performance.



Never thought of it that way but i do remember alot of smoke which = co2 which is bad. Thats probably why it did fine dry firing and sucked after i used the paper. Thanks for the help guys.
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Unread postAuthor: benstern » Tue Jan 15, 2008 9:44 pm

Smoke is not CO2... it is solid carbon based particulates produced by combustion. CO2 is a clear gas.

If you don't want to build a proper propane meter you can always use a LARGE syringe and a ball valve port.
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Unread postAuthor: frogy » Tue Jan 15, 2008 10:05 pm

You could be confusing Smoke as CO, Carbon Monoxide, which is probably the most common deadly gas released from internal combustion engines (everyday vehicles :P)

It too is clear and odorless, but the other gases released in exhaust (carbon based) give it a grayish-black color...


That syringe idea for a propane meter is cool! I've never though of that before...
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Unread postAuthor: jimmy101 » Wed Jan 16, 2008 1:20 pm

frogy wrote:That syringe idea for a propane meter is cool! I've never though of that before...

You have ~500 posts here and you've never heard of using a syringe as a meter? :shock:

LikimysCrotchus5 wrote: By this statement, do you suggest leaving the fan on when firing the combustion cannon?

Absolutely. I don't believe anyone has ever measured the precise affect of running the chamber fan during firing but it is generally believed that it will boost performance. So, wire up the fan and leave it running continuously throughout your firing session.
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Unread postAuthor: frogy » Wed Jan 16, 2008 4:40 pm

A syringe as a meter is a pretty good idea.... Jimmy take into account that I haven't been here in uhhh... since 8/9/2006... and that I don't make very many combustion cannons (normally very basic for friends or very weird for myself)...

I have made a few hybrids (really only one serious one) and went through much discussion about meter pipes on another forum (probably year+ ago), but I still have never heard of syringe metering...

Why not spend a few dollars on metal or even PVC parts for a meter though...
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Unread postAuthor: DYI » Wed Jan 16, 2008 4:58 pm

The Crusader, by Big Bang, which is arguably the most effective combustion per size ever produced, used metered MAPP in combination with single ignition near the back of the chamber, placing it behind the fan, and leaving the fan running at ignition. While the best positioning for a spark in an undisturbed chamber is clearly in the middle, running the flamefront through the moving fan seemed to increase performance considerably (although the anomalously high performance achieved was likely the result of some unexplained synergistic effects peculiar to that design, and would be difficult to replicate).

i just noticed that DYI is very good at hiding insults in his posts

:D

Syringes make excellent meters for smaller combustions, and even moreso for small hybrids (either that, or SB15's meter design). Novacastrian has used them with great success in extremely small hybrids running up to 8x with butane.
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Unread postAuthor: Kaotik Kustoms » Wed Jan 16, 2008 5:54 pm

I can't get good solid shots everytime. It seems like 1/4 of the time i get a good shot. Im using dentured alchol and it seems if i do one spray and wait about 10 seconds ive gotten the biggest bang. I've also tried starting fluid and gasoline with about the same results. Is using propane that much better? How long would a 20lb tank last?
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