Chamber fan question.

[Jumpin Jehosaphat]

I'm planning on making a metered propane combustion, and I want to use a chamber fan.

The pictures of cannons with fans confuse me. Aren't the fans exposed to the combustion when it is ignited? How do you prevent damage to a chamber fan?

[psycix]

I dont know the answer but i think chamber fans dont get damaged by the combustion, they just get warm. (correct me if im wrong)

I would like to add aswell:
What if the fan SPARKS inside!? Ehhh BOOM?

[Flying_Salt]

The fans are supposed to be in the chamber. They are exposed to the combustion, but don't get damaged, unless it's a crappy cheap fan that gets clogged with hairspray or something. But you'll be using propane so it'll be fine.

[lukemc]

I dont know the answer but i think chamber fans dont get damaged by the combustion, they just get warm. (correct me if im wrong)

I would like to add aswell:
What if the fan SPARKS inside!? Ehhh BOOM?

that is why you use computer fans they are brushless and dont produce sparks

but yea they stay intact because is only a split second of combustion

[jrrdw]

Mount it in the end cap/clean out plug. Thats what i plan on doing.

[Scotty]

You could do as i have done and mount it in the middle of the chamber using silicone. Then just drill out a hole for the wires and silicone that up.
Silicone rocks!!

Peace
Scotty

[SpudBlaster15]

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[psycix]

Another question:
Doesnt the fan block some explosion or airflow from the explosion?
It may divide your chamber into 2.

I once saw a few frame by frame pics wich showed he had 2 seperate combustions in his gun (though very very short after each other i kno) First one in the front, then one behind the fan.
It worries me....

[TwitchTheAussie]

Put the fan in the back. I had no problems destroying my cannon by mixing butane with it

[mark.f]

Another question:
Doesnt the fan block some explosion or airflow from the explosion?
It may divide your chamber into 2.

I once saw a few frame by frame pics wich showed he had 2 seperate combustions in his gun (though very very short after each other i kno) First one in the front, then one behind the fan.
It worries me....

The fan may block the actual flame front slightly, but the pressure rise will still be pretty much the same. The raise in reaction rate due to the consistent mixture and turbulence would easily make up for any obstructions to the flame front.

[psycix]

If i put the fan completly in the back, does it have any use then?
I can imagine that a fan in mid-chamber mixes more effectively..

Im thinking about fitting a very small fan (60x60mm) in my future gun so it blocks less and still can be mid-chamber, good idea or should I take the hugest fan that fits in?

[Jumpin Jehosaphat]

Thanks for all the tips guys, It seemed like fans are exposed to flames in most cannons that use them, but I just wanted to be sure.

@ psycix: It seems like a big fan will mix faster, but a small fan will obstruct flow the least. There is a trade off, you could always go with a mid sized fan.

[SnowFlox]

how much does a fan increases the combustion ?

[jimmy101]

how much does a fan increases the combustion ?

I don't think anybody knows the precise answer to that. Besides, a fan really does three things in a combustion gun.

1. It mixes the gases. This all by itself may well double the velocity that the gun shoots at. If nothing else, it will reduce the shot-to-shot variablity from perhaps 50% to ~10%.

2. If the fan is running during firing it should boost the burn rate and increase the muzzle velocity. Exactly how much is hard to say. An increase in muzzle velocity of perhaps 20% would seem reasonable.

3. The fan helps to air out the chamber between shots. That means you are much less likely to have CO2 and water vapor carrying over from shot to shot. Any CO2 or water vapor in the chamber displaces a like amount of oxygen.

[iPaintball]

Just mount the fan behind your spark gap to minimize obstruction of the flame front.