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2 chambers safe?

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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Unread postAuthor: SpudBlaster15 » Mon Aug 13, 2007 10:06 am

dongfang wrote:Hi,

The C:B ratio discussion is about the oldest one in the spudding world.....

.8:1 is optimal where you want a muzzle velocity and a small chamber size. It will give you a gun where there is no acceleration near the muzzle.

Some people consider that to be a waste of barrel -- the last 1/3 of it or so contributes very little to velocity but just makes the gun large and cumbersome. They go for a larger chamber or cut off their barrel, till they end up around 1.5:1 or something like that. Now there is good acceleration through all of the barrel, but some chamber energy is wasted (and the gun becomes louder).
Using propane, fuel will cost you like $0.02 a shot, so this needs not be considered.

Regards
Soren


If you are sitting at a .8:1 ratio, and you increase the chamber size to bring the ratio to 1.5:1, you will lose performance, because the fuel now takes much longer to burn, and thus, the initial acceleration and overall pressure in the launcher are reduced. Multiple spark gaps seem to help very little with this phenomenon. A combustion launcher will perform best at it's optimal C:B ratio, which is (depending on projectile static friction and mass) between 0.5:1 and 1:1.
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Unread postAuthor: CannonCreator » Mon Aug 13, 2007 10:48 am

but doesnt the negative and the positive have to meet up somewere, with the stun gun?
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Unread postAuthor: SpudBlaster15 » Mon Aug 13, 2007 10:51 am

Yes, meaning you can wire 2 spark gaps in series.
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Unread postAuthor: CannonCreator » Mon Aug 13, 2007 11:03 am

SpudBlaster15 wrote:Yes, meaning you can wire 2 spark gaps in series.


o ok
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Unread postAuthor: jimmy101 » Mon Aug 13, 2007 3:49 pm

A C:B of 1.5 will not perform very well. Take a look at BurntLatke's CB studies. Or a summary of the data in the SpudWiki.
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If you want to shorten the barrel without sacrificing any performance then a C:B of about 1.2 is as high as you can go. A C:B of 1.5 may well drop the muzzle velocity by as much as 50% compared to a longer barrel.

Like others have said, you only need one stungun.

Really can't think of any reason that two chambers would perform better than one of the same total volume. In fact, two chambers will probably perform a bit worse. More drag on the gases as they are choked through the coupling, greater surface area to volume ratio giving more heat loss to the gun, and probably a few other reasons.
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Unread postAuthor: sharpshooter » Mon Aug 13, 2007 6:05 pm

i am going to guarantee that you will not get both stun guns to work. sure, itll still fire, but that is because one side ignited the other. wire the spark gaps in series between the 2 chambers.

on that note, why 2 chambers? The cost of 4inch fittings is crazy. I dont have actual prices in front of me, but tee, 2 elbows, and another endcap will easily cost $50.
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Unread postAuthor: thespeedycicada » Mon Aug 13, 2007 9:37 pm

sharpshooter wrote:i am going to guarantee that you will not get both stun guns to work. sure, itll still fire, but that is because one side ignited the other. wire the spark gaps in series between the 2 chambers.

on that note, why 2 chambers? The cost of 4inch fittings is crazy. I dont have actual prices in front of me, but tee, 2 elbows, and another endcap will easily cost $50.
probaly because it looks cool also mabey if 1 chamber had a bad fuel air ratio the other would go off and ingnite the other.I dunno its just a theory
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Unread postAuthor: sharpshooter » Wed Aug 15, 2007 12:02 am

looks cool is reason enough. just go with one stun gun tho.

calculating the chamber size may prove to be rather dificult with elbows and t's and what not. Also, fueling and mixing 2 chambers will probably be more problematic.

just my $0.02 worth
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Unread postAuthor: pyrogeek » Wed Aug 15, 2007 1:24 am

2 will surely be safe. And I think that even if you had ignition in only one, it would still work. The flame is going to travel out of one, and since the potato is there, it will have to get forced into the second chamber thus igniting it. But, just use a stun gun and have either single or dual sparks in each. Or, you could make a chamber that will be hooked up to both chambers and fueld. Then a spark will be fired in it, thus shooting a flame out of it and into the chambers, creating an ignition system that should be quite unique and effective.
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