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The logic of a very tight projectile

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: Hawkeye » Fri Apr 30, 2010 12:16 pm

I think the word you are looking for is "optimum". It's not going to do much good if there is so much friction that the projectile can't even be moved by the air. In any event this idea seems so basic and common sense that it hardly bears mentioning.
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Re: The logic of a very tight projectile

Unread postAuthor: Ragnarok » Fri Apr 30, 2010 1:07 pm

boyntonstu wrote:IOW the average non-good valve gun, (you know who you are), will do better with a high friction projectile.

Try putting it into a simulator.

The figure you put into GGDT is static friction. It then, I believe, takes dynamic friction to be half that. (I can set them independently on Apocalypse, but GGDT's method is a good estimation.)

It's only very specific values of valve speed and valve flow, combined with certain ratios of barrel to dead volume that will allow an improvement in velocity when friction is increased.

Under these circumstances, the numbers show that the difference in performance comes from the reduced blow-by in the barrel, not the higher friction.

You're also subject to Hawkeye's very valid point.
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Re: The logic of a very tight projectile

Unread postAuthor: boyntonstu » Fri Apr 30, 2010 1:21 pm

Ragnarok wrote:
boyntonstu wrote:IOW the average non-good valve gun, (you know who you are), will do better with a high friction projectile.

Try putting it into a simulator.

The figure you put into GGDT is static friction. It then, I believe, takes dynamic friction to be half that. (I can set them independently on Apocalypse, but GGDT's method is a good estimation.)

It's only very specific values of valve speed and valve flow, combined with certain ratios of barrel to dead volume that will allow an improvement in velocity when friction is increased.

Under these circumstances, the numbers show that the difference in performance comes from the reduced blow-by in the barrel, not the higher friction.

You're also subject to Hawkeye's very valid point.


Is there a simulator that allows for different coefficients of friction at various points inside the barrel?

I propose a barrel that holds the projectile until pressure is built up behind it and then quickly and easily shoots down your polished and coated barrel to the muzzle.
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Unread postAuthor: psycix » Fri Apr 30, 2010 1:24 pm

Another thing to think about.
Some foamy projectiles might compress under pressure and grant a lot of blowby. I expect a significant performance increase in cases like that.
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Re: The logic of a very tight projectile

Unread postAuthor: Ragnarok » Fri Apr 30, 2010 3:57 pm

boyntonstu wrote:Is there a simulator that allows for different coefficients of friction at various points inside the barrel?

That's basically what I said about my own simulator, Apocalypse. It allows you to set the static and dynamic frictions independently of each other.

And with what qualifies as an even half way decent valve, increasing static friction does not confer any notable advantage.
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