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Can I fire my spudgun with the fan ON ?

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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Can I fire my spudgun with the fan ON ?

Unread postAuthor: nightshot » Tue Oct 28, 2008 9:31 am

yes, this is the question.. it sound stupid but i need to know o.O
So, can I fire my spudgun with the fan turned on?
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Unread postAuthor: Ragnarok » Tue Oct 28, 2008 9:41 am

Yes, it's actually very common to do so. The turbulence it causes in the chamber tends to improve performance.
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Unread postAuthor: jimmy101 » Tue Oct 28, 2008 9:46 am

Yes, you can fire a combustion spudgun with the fan running. Indeed, the gun will probably perform better with the fan running since the fan creates turbulance, which makes the fuel burn faster.

The fan should be near the breach end of the gun so there isn't a large volume of gas, moving at high velocity, blowing past the fan's blades during firing.
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Unread postAuthor: LCTChamp » Tue Oct 28, 2008 2:55 pm

Indeed you can as mentioned above. I was turning mine off, and i accidentally left it on one time and noticed a major increase in distance.
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Unread postAuthor: BigGrib » Tue Oct 28, 2008 3:05 pm

jimmy101 wrote:The fan should be near the breach end of the gun so there isn't a large volume of gas, moving at high velocity, blowing past the fan's blades during firing.


This is also to aid in installing and removing the fan as needed so one does not have to insert his/her whole arm into the chamber and get it stuck like a racoon pullin butter out of a churn.

I hope that makes sense to someone because I dont wanna have to explain it mathematically to you guys.
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Unread postAuthor: nightshot » Wed Oct 29, 2008 6:32 am

Thanks guys ;D,
So, the distance increase between a spudgun without a fan and the other with the fan turned on is very large?
An increase of 50% in distance maybe ?
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Unread postAuthor: Ragnarok » Wed Oct 29, 2008 7:55 am

nightshot wrote:An increase of 50% in distance maybe ?

It's very unlikely to be that generous, although the exact results do very much depend on the fuel, chamber shape, spark locations, fan location.
As such, I can't tell you - you'll need to go and find out yourself.

Now, if I'm forced into an answer... some spudguns get 20% or more, but 50% is on the VERY generous side.
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Unread postAuthor: starman » Wed Oct 29, 2008 9:30 am

nightshot wrote:Thanks guys ;D,
So, the distance increase between a spudgun without a fan and the other with the fan turned on is very large?
An increase of 50% in distance maybe ?


Performance increase won't be noticed as much if you are shooting spuds be cause of their irregularities and drag. Improvement will be more noticable with hardened ammo, golfballs etc.
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Unread postAuthor: nightshot » Wed Oct 29, 2008 11:07 am

starman wrote:
nightshot wrote:Thanks guys ;D,
So, the distance increase between a spudgun without a fan and the other with the fan turned on is very large?
An increase of 50% in distance maybe ?


Performance increase won't be noticed as much if you are shooting spuds be cause of their irregularities and drag. Improvement will be more noticable with hardened ammo, golfballs etc.


I´m using tennis balls ..
Well, look, I recently built a new combustion, mid-sized, to use in airsoft games :shock: , so we use tennis balls to not hurt if I hit someone, my Airsoft team let us use spudguns, but with a rule, not to aim at a person, but close to him (5 meters of distance or more), so technically the one who is close will have to call his "death" becouse of the "explosion" of the "rocket":D , I know that even with tennis ball the chance of hurt someone is dangerous so we are trying to develop a new kind of ammo, I will post the project of the ammo here in a few days...
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Unread postAuthor: jimmy101 » Wed Oct 29, 2008 12:59 pm

Ragnarok wrote:
nightshot wrote:An increase of 50% in distance maybe ?

It's very unlikely to be that generous, although the exact results do very much depend on the fuel, chamber shape, spark locations, fan location.
As such, I can't tell you - you'll need to go and find out yourself.

Now, if I'm forced into an answer... some spudguns get 20% or more, but 50% is on the VERY generous side.

I agree, if the fuel is well mixed then having the fan running during firing is probably worth 10-20% in muzzle velocity (20-30% in KE) with 10% being much more likely than 20%. A lot of things will affect the performance boost, in particular the number of spark gaps and the distance from the fan to the nearest gap, the amount of air the fan moves, the size of the fan relative to the size of the chamber (you probably want a fan diameter significantly less the the diameter of the chamber) etc.

The difference between no fan at all and a fan is much larger. I've seen a difference of nearly ten fold in range. Really poor mixing gives amazingly bad performance. Indeed, if the mixing is bad enough the gun won't fire. In that case the increase in performance due to a fan is infinite. :D
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Unread postAuthor: psycix » Wed Oct 29, 2008 5:18 pm

As said above, it doesnt make much of a difference whether you keep it running or not.
The main functions of a fan are mixing and venting, and venting actually mostly just for convenience and reloading speed.
Mixing, however, is extremely important!

My combustion used to splatter potatos against the door of my garden shack, and after a fan upgrade, I accidentally shot a potato through a board AND that door on the first shot... :shock:

A chamber fan is really a must-have for a good combustion, and its both easy to install, and super-effective!


Oh, btw, nightshot, if you read the spud wiki, there is alot of information there (like the answer of the question you asked in the topic start)
It is highly recommended to read it, as you will learn alot and all information you need to know is packed together in one place.
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