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Frictionless barrel idea

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Frictionless barrel idea

Unread postAuthor: hyperspaz » Fri Feb 26, 2010 8:13 pm

Hi guys,

I have this idea of making a frictionless barrel, but I'm unsure if it will work, or if it will even make a difference. My idea consists of a barrel with a bunch of small, evenly spaced holes in it; surrounded by another tube, that would supply air to those holes in the barrel. Which, in turn, should make the projectile float, as it travels through the barrel. It's basically the same principle as an air hockey table.

Please, let me know what you think. Thanks!
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frictionless barrel cannon.jpg
Sorry for the horrible schematic, I was in a hurry when I made it.. This isn't exactly how I would make the cannon, its just to help you better understand my idea, and how it might work.
frictionless barrel cannon.jpg (33.21 KiB) Viewed 1555 times

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Unread postAuthor: Hubb » Fri Feb 26, 2010 8:17 pm

That's almost inline with a ram accelerator (if you know what that is) except for pneumatics. If there were a way to trigger the secondary valve for the barrel as the projectile passed a certain point, it may work. I'm interested to see this go past the design stage and how much, if at all, it increases performance.
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Unread postAuthor: Hawkeye » Fri Feb 26, 2010 8:29 pm

It's still going to have air blasting into the barrel. I can envision the projectile being hit by such turbulence that it would be lucky to clear the barrel.
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Unread postAuthor: Lockednloaded » Fri Feb 26, 2010 9:07 pm

I don't understand how this works, but i think i can help simplify the design. Instead of two chambers and two pistons, why don't you just use the pilot of one piston to go to your barrel shroud thing. If this is not enough air, you could increse the pilot volume (jsr's gonna hate that :lol: ) and use a huge pilot valve. These should help make it much simpler to build

~lnl~
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Unread postAuthor: inonickname » Fri Feb 26, 2010 9:57 pm

If the force on either side is balanced then the weight of the projectile will still cause friction on the bottom of the barrel. It needs to be so that it can barely hold the projectile off the barrel.

It's fairly likely to hurt performance though.
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Unread postAuthor: Brian the brain » Sat Feb 27, 2010 12:47 pm

The idea is completely ridiculous...
I love it hahaha
But I'm fairly positive of negative results
:D
If you where to launch a ringshaped piston through the barrel schroud simultaniously you might be able to ...well...have it suck less I guess..

WTH?? I'm trying to improove on a no chance design..

Think about this..what's the difference between this design and using slightly undersized ammo??
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 27, 2010 12:58 pm

Interesting concept but flawed, there already is a thin cushion of air between the barrel and the projectile when you fire it anyway (assuming your projectile hasn't got o-rings fitted), performance gain is highly unlikely and even if there is some it would be insignificant. You're better off dedicating all that extra valving to making a semi-auto mechanism ;)
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Unread postAuthor: jimmy101 » Sat Feb 27, 2010 5:19 pm

Like Jack said. A loosely fitting ammo will pretty nearly be floating on a thin layer of blow by anyway and that's a lot easier to do than is plumbing in an extra air supply via a bunch of holes.

In addition, many guns designs (both pneumatic and combustion) benefit from a bit of friction. If not from the friction then often just the lack of blow by adds enough power that that is more important than friction.

HGDT or GGDT will let you estimate how much friction actually hurts (or helps) performance. I suspect you'll find that friction that either (1) it doesn't make much difference and can be offset with a slightly larger chamber or that (2) friction actually increases performance a bit.

(Combustion guns typically work much better with a fair amount of friction.)
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Unread postAuthor: Brian the brain » Sat Feb 27, 2010 5:23 pm

Friction allows for pressure buildup..

True.
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: inonickname » Sat Feb 27, 2010 6:31 pm

Good point with the pressure buildup. If you want less resistance in your barrel, draw a vacuum in it. Vacuum alone can propel a ping-pong ball to near the speed of sound.
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Unread postAuthor: jimmy101 » Sat Feb 27, 2010 8:14 pm

inonickname wrote:Vacuum alone can propel a ping-pong ball to near the speed of sound.

Only if by "vacuum alone" you mean the gun itself was already moving at Mach 0.5 or so.
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Unread postAuthor: Lentamentalisk » Sat Feb 27, 2010 8:16 pm

inonickname: "Vacuum alone" can accelerate anything to the speed of sound (actually to the speed of the fastest moving particles) it just takes a damn long time and zero friction. Assuming, of course, that both sides aren't vacuumed.

Its called unbalanced forces. They cause acceleration. End of story.
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Unread postAuthor: inonickname » Sat Feb 27, 2010 8:28 pm

Lentamentalisk wrote:inonickname: "Vacuum alone" can accelerate anything to the speed of sound (actually to the speed of the fastest moving particles) it just takes a damn long time and zero friction. Assuming, of course, that both sides aren't vacuumed.

Its called unbalanced forces. They cause acceleration. End of story.

Indeed, but I meant in practicality for the average spudder (not many of us are building particle accelerators). Zero friction, perfect fit and perfect vacuum is essentially out of our reach.
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Unread postAuthor: Ragnarok » Sat Feb 27, 2010 8:37 pm

I'm a little surprised that the flaw in having a barrel with holes in it hasn't been mentioned.

As far as friction, it's largely irrelevant in a spudgun barrel - the equivalent of a couple of dozen kPa compared to numbers of several hundred or even thousands. If you're that fussed, my suggestion is to get a PTFE spray, squirt it down the barrel and that should reduce friction just fine.

I do have a project with a frictionless barrel (and indeed, frictionless "rifling"), but it's electromagnetic, not pneumatic.
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Unread postAuthor: Hawkeye » Sat Feb 27, 2010 9:31 pm

Better to use the second piston to work a gas ram that operates a loader.
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