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Where to put the 80mm fan?

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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Where to put the 80mm fan?

Unread postAuthor: taterflames22 » Mon Dec 15, 2008 12:37 pm

I'm wondering if anyone could help me out. When putting the fan in the chamber, do you put it behide the gas output or in front of the gas output?
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Unread postAuthor: starman » Mon Dec 15, 2008 1:06 pm

Not sure what you mean by the "gas output". You typically install the fan at the rear of a chamber. I usually place the fuel meter input directly in front of the fan. Place it where it blows down the chamber and out of the breech, sucks fresh air from the back side.
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Last edited by starman on Mon Dec 15, 2008 2:46 pm, edited 1 time in total.
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Unread postAuthor: taterflames22 » Mon Dec 15, 2008 1:41 pm

Thats what I meant, the fuel meter input. Basically when the gas goes in the chamber. Thank you for your help!!
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Unread postAuthor: jimmy101 » Mon Dec 15, 2008 2:10 pm

The relationship between the fan and the fuel injection point really shouldn't matter. If the fan is effective at mixing then where the fuel starts is irrelevant. In a spray-n-pray setup a large fan will tend to be in the way of the spray. Hopefully, any liquids in the spray that settle on the fan will vaporize quickly once the fan is turned on.

Usually, the fan is placed near the breach end of the chamber. This is the easiest place to put it and reduces the shock loads on the fan. The fan will usually last longer at the breach. If the fan is placed near the chamber barrel junction then it is subjected to the high velocity gas flow when the gun fires. The fan might not like being subjected to gases moving at a couple hundred miles per hour.
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Unread postAuthor: Xxplosive42o » Mon Dec 15, 2008 4:31 pm

An ideal place for the fan would be at the aft end of the cannon directly behind the fuel meter input. This allows the fan to push the fuel evenly through the chamber and mix accordingly. I do not know if it really matters if it goes before or after, but thats just my take on it. In a spray-n-pray model like Jimmy noted, it will tend to get in your way while spraying into the chamber so make sure you use a flammable spray that doesn't gunk your chamber like hairspray does. Use static guard or a substance similar. Here is a model of the chamber fan being behind the fuel input.

Image[/img]
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Unread postAuthor: jimmy101 » Tue Dec 16, 2008 11:49 am

Xxplosive42o wrote:An ideal place for the fan would be at the aft end of the cannon directly behind the fuel meter input. This allows the fan to push the fuel evenly through the chamber and mix accordingly.

That really doesn't matter. If the fan is effective at mixing then it is effective no matter where it is placed relative to the fuel injection point.
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Unread postAuthor: psycix » Wed Dec 17, 2008 9:57 am

Fan placement doesnt matter much when its about mixing.

One thing to note tough is that a fan thats not placed in the back will have to let air from the back flow past it to the front.
This may cause flow restriction, and when the fan is WAY to far up front (near barrel) the fan blades break off.

On top of that, a fan thats in the back can be taken out easily for service on the chamber insides.
So based on these points back would be best.
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Unread postAuthor: Radiation » Wed Dec 17, 2008 7:46 pm

Fan size is more important than fan location (though I scoff at the notion that putting a fan at the end of a chamber is an ideal setup). People tend to use a fan that is way too big for their chamber. The Latke picture is a perfect example of that. An overly large fan does not properly mix the fuel at the opposite end of the chamber fast enough. It tends to just blow air within close vicinity of the fan. A smaller fan on the other hand will allow the air inside the chamber to circulate behind and in front of the fan more readily. They might take a bit longer to vent the chamber, but I find overall it's much better.

The Gauntlet (click on my sig to see) has a 2" fan in a 3" chamber.
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