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distence problems

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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distence problems

Unread postAuthor: redalpha11 » Fri Aug 08, 2008 10:08 pm

so i am done sleeving my cannon. i have redisged the sparker position and where the sparker arks and everything all i have to do now is just touch it up cosmetically. but besides that it just dosnt fire very far it will fire about 20 or so feet. i am just a little concerned about the distance of it. the cb ratio is about .7 to 1 . i am using a off brand body spray that has a whole lot of butane in it. and it is really flammable. so i am just wondering how i could extend the rang a lot. pics to came towmarrow.
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Unread postAuthor: TurboSuper » Fri Aug 08, 2008 10:15 pm

Urr, the C:B ratio is a bit low for an aerosol combustion, still...20 feet ain't much. What's the chamber diameter? I find ones with a narrow chamber get barely any range.
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Unread postAuthor: BC Pneumatics » Fri Aug 08, 2008 10:47 pm

If this is your first cannon, you may not be familiar enough with the amount of fuel you need. Try covering a broader spectrum next time you shoot. Start with much less than you normally use, then gradually increase until you are well past what you used when you got 20'.
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Unread postAuthor: brogdenlaxmiddie » Fri Aug 08, 2008 10:50 pm

I agree with BC Pneumatics. Your fuel is prolly to rich.
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Unread postAuthor: starman » Fri Aug 08, 2008 11:02 pm

Also, are you fitting your projectile in reasonably tight? Potato? If it's too loose, you'll lose some power.
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Unread postAuthor: jimmy101 » Sat Aug 09, 2008 11:43 am

Do you have a chamber fan? A fan is probably the most important addition to a combustion gun, more important than metered fuel or multiple spark gaps.

To see if a fan would help, without actually installing one, fuel the gun and let it sit for an hour or two, occsionally inverting the gun. You need an airtight spud in the barrel so the fuel doesn't escape. After the wait, fire the gun. If your performance goes way up (as in 20 ft to 300ft) then poor mixing is the problem and a fan will fix that. If performance doesn't go way up then your problem is probably too much fuel in the chamber.

Brushless CPU fans are the preffered fans but they can be a bit pricey and there's a good chance you'll have to order it online. A cheapo chamber fan can be made from a "personal" fan (hand held, battery operated, often with a foam rubber blade) that you can usually find at stores like Kmart for a couple bucks.
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Unread postAuthor: sirspuddest » Sat Aug 09, 2008 11:38 pm

jimmy101 wrote:Do you have a chamber fan? A fan is probably the most important addition to a combustion gun, more important than metered fuel or multiple spark gaps.

To see if a fan would help, without actually installing one, fuel the gun and let it sit for an hour or two, occsionally inverting the gun. You need an airtight spud in the barrel so the fuel doesn't escape. After the wait, fire the gun. If your performance goes way up (as in 20 ft to 300ft) then poor mixing is the problem and a fan will fix that. If performance doesn't go way up then your problem is probably too much fuel in the chamber.

Brushless CPU fans are the preffered fans but they can be a bit pricey and there's a good chance you'll have to order it online. A cheapo chamber fan can be made from a "personal" fan (hand held, battery operated, often with a foam rubber blade) that you can usually find at stores like Kmart for a couple bucks.


Chamber fans can be a little expensive if you buy them new, especially the Radio Shack brand fans.

Most used electronics stores will either give them to you for free, or very, very cheaply.

Never even thought to try the handheld ones, though.
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Unread postAuthor: starman » Sun Aug 10, 2008 12:02 am

sirspuddest wrote:Chamber fans can be a little expensive if you buy them new, especially the Radio Shack brand fans.

Most used electronics stores will either give them to you for free, or very, very cheaply.


Nah, they can be had fairly inexpensively. Radio Shack has possibly the highest priced computer fans known to all of mankind.

And yes, computer salvage shops have them running out of their ears. Many of them are pretty worn out though but they can very likely hook you up with several for cheap or free.
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Last edited by starman on Sun Aug 10, 2008 11:53 am, edited 1 time in total.
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Unread postAuthor: BC Pneumatics » Sun Aug 10, 2008 1:49 am

<a href="http://www.bcarms.com/product_info.php?cPath=45_47&products_id=30">Might try one of these...</a>
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Unread postAuthor: TurboSuper » Sun Aug 10, 2008 9:27 am

Latke's testing only revealed a 30% or so power increase with a chamber fan. I'm pretty sure there are other factors at play here if he's only getting 20 feet.

Either bad projectile sealing, or too narrow a chamber are my bet. Would be helpful to see some pics.
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Unread postAuthor: jimmy101 » Sun Aug 10, 2008 11:40 am

TurboSuper wrote:Latke's testing only revealed a 30% or so power increase with a chamber fan. I'm pretty sure there are other factors at play here if he's only getting 20 feet.

Latke used a fuel meter which appears to give pretty good fuel mixing. I know from experience that a chamber fan can boost range by a factor of five or more when fueling is done with a syringe. It all depends on how well the fuel is mixed during injection.

In addition, I believe Latke's fans are pretty close to the same diamter as the chamber. That's probably not the best size for maximizing performance.

Of course, crappy performance could also be from poor fitting ammo, really rich fuel mixture, massive leaks in the chamber ...
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Unread postAuthor: redalpha11 » Sun Aug 10, 2008 6:58 pm

well it turned out that i was not using enough fuel. so i added like 5 seconds now and it is going 100 feet i am pretty pleased with the results since it is a first cannon with such a small c:b ratio. but over the next couple of months or so i will be making another one with a chamber fan and all the other things that could make it really good. also thank you for all the help guys i am happy that there are such nice helpful people on this forum that are willing to give me advice for my cannons.
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Unread postAuthor: psycix » Tue Aug 12, 2008 3:35 pm

I'd bet 100 bucks on that he's using way too much fuel,
Everybody does that at the beginning. I did too.

So there are 3 options:
-Use way less fuel.
-Install propane meter
-Add some pure oxygen :D

(That last one is sarcastic, do not do that since your gun will explode and embed itself into your vital organs. Unless your gun is out of thick metal.)
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Unread postAuthor: BC Pneumatics » Tue Aug 12, 2008 4:25 pm

Erm, psycix, he just posted saying he had not used enough fuel...
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Unread postAuthor: McFear » Wed Aug 13, 2008 6:35 am

lol, you gotta love slow people.
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