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Unread postAuthor: starman » Fri Jan 09, 2009 12:05 am

MrCrowley wrote:The fan, well no one has tempted it before and people seem to agree it makes little difference.


HGDT calculations indicate that a fan will improve performance. I'm planning one for a hybrid build as well.

@moonbogg; Good job man.... :wink:
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Unread postAuthor: inonickname » Fri Jan 09, 2009 12:16 am

Awesome, lucky to get free work like that done.

Cool design also, which cad program did you use?
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Unread postAuthor: Moonbogg » Fri Jan 09, 2009 12:36 am

I have a fan because it is a combustion/hybrid. I will be using it as an advanced combustion sometimes and other times a hybrid. I figured the fan couldn't HURT the hybrid performance. it functions as both. Never built a hybrid before, so this input is very valuable to me.
I have the pressure guage to see the pre ignition chamber pressure, and I agree it should be protected somehow. I could just put a valve between it and the chamber.
The valve is there to clear the chamber of course. I wonder why hybrids don't need one. This one does though, since its also a combustion gun for shooting potatoes and lemons etc. It certainly won't weaken the gun.
The gun will operate at a 2-3x.

Edited: use Solidworks 2009.
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Unread postAuthor: MrCrowley » Fri Jan 09, 2009 12:44 am

Instead of the ball valve, you should be able to run compressed air through the Quick Connect, it should push it all out the barrel. Though this limits portability.
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Unread postAuthor: Moonbogg » Fri Jan 09, 2009 12:48 am

MrCrowley wrote:Instead of the ball valve, you should be able to run compressed air through the Quick Connect, it should push it all out the barrel. Though this limits portability.


You got that right, and thats exactly why it has a fan and ball valve. Oh, and the work isn't free. Its coming back to them, believe me. They will make sure of it. For now its a huge relief though.
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Unread postAuthor: inonickname » Fri Jan 09, 2009 1:23 am

Ohh I was under the impression they were using the plans as payment or something like that :\ oh well..cool anyway
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Unread postAuthor: jackssmirkingrevenge » Fri Jan 09, 2009 1:34 am

Are you sure you're not ecstatic? ;)

Good luck on getting it made, looks like it will be a blast :)
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Unread postAuthor: Moonbogg » Fri Jan 09, 2009 2:11 am

jackssmirkingrevenge wrote:Are you sure you're not ecstatic? ;)

Good luck on getting it made, looks like it will be a blast :)


Lol, yeah thats what I meant.

inonickname wrote:Ohh I was under the impression they were using the plans as payment or something like that :\ oh well..cool anyway


Now THAT would have been really awesome.
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Unread postAuthor: Hotwired » Fri Jan 09, 2009 3:59 am

I hope that's an error on the diagram.

It's not the bit where you have the reinforced bend coming off the chamber.

It's the bit where you have a large barrel a couple of metres long that appears to be supported while open on one T with a nice long section for the barrel but held down... with a jubilee clip?

I'd be concerned about what happens at that point when the barrel is leaning about while open.



Hope it won't take you forever to get their CAD drawings done to pay for it ^^
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Unread postAuthor: Moonbogg » Fri Jan 09, 2009 5:51 am

Whats a jubilee clip? The only purpose the barrel support serves is to hold the barrel for sliding it forward and backward. It is pipe strapped down and will be very strong, so any hold down support it gives the barrel would be a plus. Since the barrel slides forward and back, there must be some amount of play there, so I couldn't rely on it for true support. Thats why the back end is built like a tank.

Edited: Oh, and that barrel weldment only weighs 3lbs. So it doesn't take much to support it while its cantilevering. wait...I fixed it. New support in place. 10" shaft collar
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Unread postAuthor: jackssmirkingrevenge » Fri Jan 09, 2009 6:20 am

Moonbogg wrote:Whats a jubilee clip?


Image

Hose clamp ;)
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Unread postAuthor: Fnord » Fri Jan 09, 2009 11:30 am

The fan, well no one has attempted it before and people seem to agree it makes little difference.



I've tried it before. Twice. The first time I couldn't really tell the difference in power, but the bang seemed a bit sharper than normal. The second hybrid fan setup I did gave quite a noticeable noise difference, though testing was never done as that hybrid is temporarily in a non-working state.

Also, the second fan got corroded or something and now only works well on 18 volts. I'm making an explosion/moisture-proof one though.

(Edit: It should be noted that I put my fans in lengthwise, rather than have them blocking the chamber. It gives more flow and doesn't expose the fan to high pressure differentials).
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Unread postAuthor: psycix » Fri Jan 09, 2009 12:20 pm

The three functions of a fan are:
-Mixing
-Venting
-Inducing turbulence -> increasing burn speed.

Well, mixing is done in a hybrid by the air pressure flowing in and venting can also be done that way. Just flush the chamber with a burst of fresh air every shot. That makes fans unnecessary as their two main functions are not needed anymore.
Only inducing turbulence (which is the smallest effect of all) can do something in a hybrid.
I believe though, that chance on DDT increases.
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Unread postAuthor: jimmy101 » Fri Jan 09, 2009 1:53 pm

I don't agree with psycix on the ability of the fuel +air to mix in a hybrid without a fan. I doubt the blast of air during fueling is sufficient to fully mix the chamber. It probably comes pretty close but a fan will still help.

The fan will still help with venting, even if you use a blast of compressed air for venting. The fan will still increase the burn rate.

The only concern I would have with a fan is the much greater probability of breaking it when the gun is fired as a hybrid. I would definetly design the gun so the fan can be easily replaced. I would also make sure it's a brushless fan.

How is the recoil from the barrel transfered to the chamber? The forward connection between the two is the support for the barrel when loading right? It won't atually transfer the recoil to the chamber. That means all the recoil is passed to the chamber via the elbows? Not good. I think you need bracing somwhere else in the system. Perhaps put a coupler in the barrel just in front of the barrel guide so that when the breech is closed the coupler is pressed back against the support.

Dave's suggestion of a needle valve between the chamber and gauge is a good one. That gives you one less valve that needs to be opened/closed during loading and firing. A needle valve is the hydraulic equivalent of a low pass filter in electronics. It will pass, without any modification, slow changes in pressure. It will block fast changes in pressure. The only tricky part is deciding just how big the orifice should be. I would suspect that it needs to be pretty darn small. A disk with a small hole, probably less than 0.01" might work. The nozzle of a Bernzomatic torch head has a hole that is probably less than 0.01" in it and would work pretty well as the flow restrictor. With a small enough hole the flame won't propagate through it even if their is a combustable mixture on the other side.

The design looks good, just make sure there is sufficient bracing between the barrel and chamber.
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Unread postAuthor: Moonbogg » Fri Jan 09, 2009 3:22 pm

jimmy101 wrote:How is the recoil from the barrel transfered to the chamber? The forward connection between the two is the support for the barrel when loading right? It won't atually transfer the recoil to the chamber. That means all the recoil is passed to the chamber via the elbows? Not good. I think you need bracing somwhere else in the system. Perhaps put a coupler in the barrel just in front of the barrel guide so that when the breech is closed the coupler is pressed back against the support.


THIS is a damn good idea and it will be used for sure. I was struggling with a way to remove strain from the return pipe in the back and this idea kicks all the ass. Seriously, thank you. I will beef up that barrel support and let it restrict that elbow from trying to unroll itself. I knew I couldn't rely on the support for its ability to hold the barrel DOWN when the elbow tries to lift it up because the support has play in it. Even a tiny bit of play is too much at those pressures. But like you said I can use it for in-line support perfectly.


jimmy101 wrote:Dave's suggestion of a needle valve between the chamber and gauge is a good one.


Thanks also for repeating this suggestion. It is excellent and will be used. This is the kind of stuff that gets me excited. The more heads that can be put together to come up with a design, the better. Starman gave some good tips already, and will likely have saved my gauges from being banged around to hell and back. Good stuff here.

Oh, the compressed air thing to vent the chamber would be great, but I plan on going out to the mountains and desert with this thing and I won't want to lug around an air compressor.
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