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Performance enhancement

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: Daltonultra » Mon Dec 08, 2008 3:47 pm

I'm looking at the chamfer of the piston sealing face of the barrel, and I can't help but think the air flowing across the edge of the pipe is going to pinch some of the flow. Basically, turbulence generated by flowing across the edge forms a boundary-layer vortex just inside the tube, choking the actual intake area down a small percentage. I assume you know about that, and the chamfer is to counter that.

There's a design used in extremely high performance cars called a velocity stack. It literally looks like the bell of a trumpet.

Wikipedia's entry on it has a very good explanation on the physics of it.
http://en.wikipedia.org/wiki/Velocity_stack

If you're getting down to "every last little bit", it'd be interesting to see the effect.
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Unread postAuthor: Ragnarok » Mon Dec 08, 2008 6:24 pm

ALIHISGREAT wrote:Modified 1/2" QEV?!?! what much can you do to improve it?

The trick is not so much as to increase the flow of the QEV, but to reduce the amount of air that needs to flow through it.
A 1/2" QEV has a large amount of empty space in it which goes to little use, and adds extra pilot volume. The aim therefore is to modify the QEV to act better as a pilot valve, by reducing it's internal volume without sacrificing the flow.
Basically modify it to how it should have been in the first place.

maybe an electronic trigger would be good? a mini-solenoid to pilot the QEV?

It was an idea I had considered, but eventually I decided that the current slide valve pilot for the QEV was more than sufficient, although I am going to cut the pilot volume for the QEV somewhat as well.
An electronic trigger system could improve consistency, but it will also be on the side of very small gains for a fairly great cost. Also, it adds an electrical dependence for the launcher. I have ideas for electrical additions the launcher doesn't rely on, but I'd rather not have things it has to rely on.

Daltonultra wrote:Basically, turbulence generated by flowing across the edge forms a boundary-layer vortex just inside the tube, choking the actual intake area down a small percentage. I assume you know about that, and the chamfer is to counter that.

That was exactly the plan, except I'm planning to try and do a better job of it than when I did it on HEAL.

Obviously, the velocity stack idea can't be directly applied, but these are my ways to try and get a similar effect.
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Unread postAuthor: LCTChamp » Mon Dec 08, 2008 6:59 pm

Your title "performance enhancement" made me think of a Viagra commercial. :lol: Back on topic, does anyone have a link to HEAL, because I don't think I have seen it before.
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Unread postAuthor: VH_man » Mon Dec 08, 2008 7:05 pm

lctchamp wrote:Your title "performance enhancement" made me think of a Viagra commercial. :lol: Back on topic, does anyone have a link to HEAL, because I don't think I have seen it before.


Haha it did for me too.... But I saw its creator and I realized who made it, and decided not to comment.....

that and how have you NOT heard of the HEAL?

That and Rag, I finally understand why your piston inlet is cone-shaped. Interesting. I might just have to try that.

Also, Just a thought on efficiency more, Try making the Inlet to the Barrel not "ragged". Kinda like, Make the Barrel inlet a soft cone leading out to the edge of the Piston housing. This will proboably fix things up more than anything.
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Unread postAuthor: Ragnarok » Mon Dec 08, 2008 8:19 pm

lctchamp wrote:Your title "performance enhancement" made me think of a Viagra commercial

You're all dirty minded punks. :violent1:

VH_man wrote:Also, Just a thought on efficiency more, Try making the Inlet to the Barrel not "ragged". Kinda like, Make the Barrel inlet a soft cone leading out to the edge of the Piston housing. This will proboably fix things up more than anything.

It was smoother than those photos show, those were half way during construction.

Hopefully, 3vo will improve what HEAL did even further.
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Unread postAuthor: VH_man » Tue Dec 09, 2008 6:29 am

Ragnarok wrote:
VH_man wrote:Also, Just a thought on efficiency more, Try making the Inlet to the Barrel not "ragged". Kinda like, Make the Barrel inlet a soft cone leading out to the edge of the Piston housing. This will proboably fix things up more than anything.

It was smoother than those photos show, those were half way during construction.


Bah. I didnt explain that well. I mean:

Fill in the area from the edge of the sealing "area" of the barrel to the front of the piston housing, with some kind of cone shaped thing. This would, as I PRESUME, make it much easier for the air to enter the barrel. If I was still awake atm id make a picture.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 09, 2008 8:46 am

Since performance is your goal, why not go for a burst disk? Your rate of fire would of course be somewhat reduced, but then again you don't exactly need it for AA defence either ;)
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Unread postAuthor: ALIHISGREAT » Tue Dec 09, 2008 12:28 pm

jackssmirkingrevenge wrote:Since performance is your goal, why not go for a burst disk? Your rate of fire would of course be somewhat reduced, but then again you don't exactly need it for AA defence either ;)


i think we all know burst discs aren't quite the same :wink: although maybe a pneumatically triggered burst disc? using air from the chamber?
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Unread postAuthor: rp181 » Tue Dec 09, 2008 1:31 pm

How do you plan to coat the interior of the barrel with Teflon? The friction coefficient will be utterly useless if you can't apply it smooth. Your best pet would be to use a larger barrel, but the inside there is a Teflon insert. Using a sharp drill bit and boring out a Teflon rod would be good, or just buy a tube. HDPE would be a good lower cost alternative, easier to machine too.
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Unread postAuthor: POLAND_SPUD » Tue Dec 09, 2008 2:40 pm

Using a sharp drill bit and boring out a Teflon rod would be good, or just buy a tube. HDPE would be a good lower cost alternative, easier to machine too.
don't you think that all in all it'd be cheaper to use helium instead of air or up the pressure?? what's the point in spending a lot of $ on teflon to get maybe 2% more power??
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 09, 2008 2:42 pm

ALIHISGREAT wrote:i think we all know burst discs aren't quite the same


Certainly not as practical as pistons but if performance is the goal, burst disks have no equal aside from "valveless" designs.

I thought you could buy dry lube spray, not sure if it's teflon.
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Unread postAuthor: Ragnarok » Tue Dec 09, 2008 3:11 pm

jackssmirkingrevenge wrote:Since performance is your goal, why not go for a burst disk? Your rate of fire would of course be somewhat reduced, but then again you don't exactly need it for AA defence either ;)

I want performance, but within other limitations - the second stage of the project will add a semi-auto mechanism.

I don't really want to sacrifice rate of fire for what little performance a burst disc will add (a few m/s at the outside). Although I so have ideas for how to handle semi auto burst discs, it's not a simple or cheap mechanism to build.

As for the Teflon issue, I already have a dry Teflon spray. My experience is that it holds pretty well, but I don't know exactly how it will fare in a barrel.

I'm also not looking to use helium. I could... but it would be far more expense than I want to go to.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 09, 2008 3:24 pm

Ragnarok wrote:what little performance a burst disc will add (a few m/s at the outside).


Are you sure the difference will be so little?

My performance data comparing similarly sized and pressurised piston and burst disk guns was as follows, this is for a 16 grain pellet:

piston valve - around 565 feet per second

burst disk (actually had around half the chamber volume of the piston valved launcher) - 720 feet per second
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Unread postAuthor: Ragnarok » Tue Dec 09, 2008 3:37 pm

jackssmirkingrevenge wrote:Are you sure the difference will be so little?

Pretty confident, yeah.

The differences I'm modelling - not with GGDT mind you, I'm using my own modeller for this, which handles various things differently and accounts for some others I know GGDT ignores - the results provided by a burst disk aren't really worth the extra effort and cost I'd have to put up to have a burst disc.
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Unread postAuthor: psycix » Tue Dec 09, 2008 3:40 pm

POLAND_SPUD wrote:what's the point in spending a lot of $ on teflon to get maybe 2% more power??

Whats the point of building one of the best pneumatic spudguns in the world (possibly the most powerful one of its size) when you know that someone who smacked a bit more money on the project would outperform you?

And on such high speeds, 2% is alot.
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