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fans.....

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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fans.....

Unread postAuthor: Marffy » Sat Nov 07, 2009 12:17 am

so putting fans in your combustion chamber allows you to have a gas vapor stay a vapor in the chamber. where do i place it so the fan doesn't blow up?
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Unread postAuthor: jmadden91 » Sat Nov 07, 2009 12:28 am

It mixes the fuel, it creates turbulence and it vents the chamber after firing. It is generally placed at the back, it will not blow up unless you are Moonbogg :p lol. Look at the WIKI
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Unread postAuthor: starman » Sat Nov 07, 2009 1:00 am

Place it as far away from the breach as possible, that's usually in the rear of the chamber furthest from the barrel transition where the massive shock, heat and outflow is felt that most.
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Unread postAuthor: rikukiakuchiki777 » Sat Nov 07, 2009 5:36 am

Marffy, A lot of people have already said this in response to some of your other posts, but please - look around the site before creating a new thread. If you check out the combustion cannon showcase, most of the cannons posted in there will have chamber fans. Observe how they were placed and do a bit of research.

But in response to your question: the fan should be placed near the rear of the chamber. If your using an threaded clean out cap, the fan can be placed on the inside of the cap/just inside the chamber where the cap screws into. You won't have a problem with breaking a fan unless it is, as stated above, near the breech where it is subject to more force.
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Unread postAuthor: jimmy101 » Sun Nov 08, 2009 11:21 am

Starman and rikukiakuchiki777

Breech? Most combustion spudguns do not have a breech. The ones that do may have the breech at the back of the chamber or at the beginning of the barrel. In the first case the fan is near the breech. In the second the fan is far from the breech.

The fan shold always be placed near the end of the chamber oposite the barrel, regardless of the location of the breech.

The maximum loading on the fan may well occur after the ammo has left the barrel, especially if the fan is near the chamber to barrel junction.
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Unread postAuthor: rikukiakuchiki777 » Mon Nov 09, 2009 12:10 am

I must have confused myself. By breech I simply meant the start of the barrel, closest to the chamber.
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Unread postAuthor: cfb_rolley » Sat Jan 23, 2010 1:43 am

on this topic, i was thinking about building a small spray and pray with a short chamber, about 9-10" and whether i have a chamber fan or not decides if i have it as a breach load or not, due to the fan being in the way. would a chamber fan really be all that needed in a small chamber like that?
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Unread postAuthor: BigGrib » Sat Jan 23, 2010 3:33 am

why would you put a chamber fan on a spray and pray, no need. i would hold off on the chamber fan until you're ready to go to a more advanced combustion.
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Unread postAuthor: rikukiakuchiki777 » Sat Jan 23, 2010 7:12 pm

BigGrib wrote:why would you put a chamber fan on a spray and pray, no need. i would hold off on the chamber fan until you're ready to go to a more advanced combustion.


I built my first spray n' pray without any modifications such as a chamber fan or dual ignition. The results we're ok, however after researching a bit I decided to implement both of the above mentioned mods. The results we're spectacular. Performance and reliability we're significantly improved, even using hairspray as a fuel. It is not that much of a hassle to install a chamber fan, so I would recommend it for any combustion launcher.
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Unread postAuthor: starman » Sat Jan 23, 2010 8:10 pm

jimmy101 wrote:Starman and rikukiakuchiki777

Breech? Most combustion spudguns do not have a breech. The ones that do may have the breech at the back of the chamber or at the beginning of the barrel. In the first case the fan is near the breech. In the second the fan is far from the breech.

The fan shold always be placed near the end of the chamber oposite the barrel, regardless of the location of the breech.

The maximum loading on the fan may well occur after the ammo has left the barrel, especially if the fan is near the chamber to barrel junction.


Yeah I know I'm a little late responding...

Yes all combustion spudguns most definitely have a breech...that being defined as the non-muzzle end of the barrel purely and simply....and exactly how my explanation presented it. You mostly said the exact same thing I did.
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Unread postAuthor: cfb_rolley » Sat Jan 23, 2010 10:36 pm

rikukiakuchiki777 wrote:
BigGrib wrote:why would you put a chamber fan on a spray and pray, no need. i would hold off on the chamber fan until you're ready to go to a more advanced combustion.


I built my first spray n' pray without any modifications such as a chamber fan or dual ignition. The results we're ok, however after researching a bit I decided to implement both of the above mentioned mods. The results we're spectacular. Performance and reliability we're significantly improved, even using hairspray as a fuel. It is not that much of a hassle to install a chamber fan, so I would recommend it for any combustion launcher.


my larger launcher is still spray and pray, and without the chamber fan it hardly ever fires properly. but, i'm thinking that may be because the chamber is fairly long, with a smaller one i'd guess that the force of the spray alone should be enough to mix it through the chamber, am i right? unless, like mentioned before, the fan keeps the spray as a vapour rather than letting it settle...?
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Unread postAuthor: paaiyan » Sun Jan 24, 2010 12:16 am

Depending on your accellerant of choice the spray may not be a vapor to begin with. Either you're using something that's a flammable liquid atomized into very small droplets, or it could be that the substance of the spray isn't your fuel, it could be the propellant that you're getting ignition from. Either way the fan's purpose is to agitate the mixture and promote a more homogeneous mixture of fuel and air.

The usefulness of a fan in a spray n pray cannon is subject to some debate, but I wouldn't think it worth the trouble since you're not bothering to try for a stoichiometric mix anyway.

With a longer chamber it may have some effect though.
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Unread postAuthor: SpudBlaster15 » Sun Jan 24, 2010 1:14 am

A chamber fan most definitely increases the performance of a spray n' pray.

Burnt Latke's Chamber Fan Data

Average velocity with starting fluid and no fan = 485.2FPS

Average velocity with starting fluid and fan = 565.2FPS
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Unread postAuthor: McCoytheGreater » Sun Jan 24, 2010 2:34 am

jimmy101 wrote:Breech? Most combustion spudguns do not have a breech. T


My gun has a breech. And a chamber fan. But my fan isn't near the breech at all.
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Unread postAuthor: cfb_rolley » Sun Jan 24, 2010 4:37 am

hmm well with my one, i'm more going for a small and easily portable cannon, performance isn't the biggest issue but reliability is as always. from what i'm gathering here, in a small chamber, a fan probably wouldn't be needed to mix the propellant but in a longer chamber (like my other one), it would definately help to make a more reliable cannon (from my own experiences). and in general, it does increase performance but my guess that the actual amount of improvement would differ from cannon to cannon.

with spray and pray, stoichiometry is out the window really, so no matter what, there'll always be that element of unreliability. in a propane/MAPP cannon, i'd say that both metering AND proper mixing of the fuel would be equally important, thus a fan probably shouldn't be left out, since you'd be going to the trouble of setting it up for propane/MAPP anyway.

...i think i understand?
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