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A question on over/ under guns

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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A question on over/ under guns

Unread postAuthor: cowkiller » Sat Nov 15, 2008 12:27 am

If the chamber is below the chamber the barrel does that reduce the pressure that is delivered to the projectile?

I was just thinking about here in kansas we have old missile silos and i know when they were made the hallways and all had a lot of 90 degree bend to slow or stop what ever, in case say a rocket motor went off on accident.
I was just sitting here looking at guns and remembered that let bit of info I learned from some guy I worked with. If i am wrong or it does not apply to this application please let me know.
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Unread postAuthor: MrCrowley » Sat Nov 15, 2008 12:42 am

If the valve is before the bends, that means the space between the valve and the projectile is 'dead space'. This means the gas in the chamber has to fill this 'dead space' before reaching the projectile, reducing pressure, which means less force on the projectile and less performance overall.

If the valve is after the bends, performance will hardly suffer as a result of the 90* bends.

Edit: Damn should've looked at the forum section, and I thought I was finally helping someone out after lounging around on this forum for two years :D
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Last edited by MrCrowley on Sat Nov 15, 2008 2:19 pm, edited 2 times in total.
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Unread postAuthor: jimmy101 » Sat Nov 15, 2008 11:08 am

It's a combustion, valve position is irrelevant since it ain't got one. :oops:

Bends in the plumbing between the bulk of the chamber and the ammo in the barrel will indeed reduce performance a bit. Partly because of the drag between the moving gases and the bends. Normally though that drag is probably pretty minor. The larger affect in a combustion is probably the increased heat loss you get as the hot moving gases go around the bends. Turbulent flow and all that will increase the rate of heat loss. Hard to say just how significant that is but my WAG is that it to is fairly minor. Minor enough that I woudn't worry about it.

I think the most significant drawback of bends is the difficulty in getting the fuel to mix around the bend. All that volume is part of the combustion chamber and even with a chamber fan you might not get thorough mixing. Poor mixing can have a pretty significant affect on performance.
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Unread postAuthor: psycix » Sun Nov 16, 2008 6:38 pm

On top of it, your flamefront needs to get into the bends for all fuel to burn.
Adding a spark gap IN the bends would certainly help.
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