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An interesting accident

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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Unread postAuthor: Combustion Monkey » Thu Jan 22, 2009 10:48 pm

Yes, I have seen that vid, but thanks for putting it up here again. Everyone running combustions should see that. It is actually what i'm gauging my cannon's performance by. Do you use just one layer of masking tape for the burst disk?

I would like to stay with my breach loading coax setup just to be different, but that is very nice. I have thought about going to a system like you use in the vid. I'd most likely get back a 100in3 of chamber volume by removing the coax barrel. With a proportionately longer barrel and MAPP gas my FPS would be pushing 800 with a golf ball by using HGDT.
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Unread postAuthor: starman » Thu Jan 22, 2009 11:04 pm

Combustion Monkey wrote:Do you use just one layer of masking tape for the burst disk?


That's 3 layers of 2" Scotch Blue Painters Tape...roughly 65 psi burst pressure based on my compressed air tests. 4 layers would actually occasionally fully contain the ignition, about 80 psi or so.... :shock: so I backed off to 3.

BTW the 3" noise stumps require 7 layers to equal about the same pressure! Takes a while to get those ready to fire.
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Unread postAuthor: Combustion Monkey » Thu Jan 22, 2009 11:10 pm

I'll have to try the "burst tape" setup, i have some of that tape kicking around. Now to retrofit the cannon to take a breach loading, quick swap out version of your rig, the fun never ends :lol: ...
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Unread postAuthor: starman » Thu Jan 22, 2009 11:22 pm

Combustion Monkey wrote:I'll have to try the "burst tape" setup, i have some of that tape kicking around. Now to retrofit the cannon to take a breach loading, quick swap out version of your rig, the fun never ends :lol: ...


Good deal. You don't have to go for the full coupler setup if you don't want to. If you have the male adapter on your barrel, you can install it directly there. It's just harder to work with the full barrel especially when trimming off the tape edges. Here's a barrel ready to fire....

Image

Just muzzle load the ball...it will stick to the tape adhesive when seated.
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Unread postAuthor: Combustion Monkey » Thu Jan 22, 2009 11:29 pm

That is really a very clean rig. I need to do something like that to work with my coax setup. Shouldn't be much more than getting some fittings. I may be the first person to house a 2in camlock in a 3in camlock, but i know the parts are on the shelf in town. And after all, its nothing a dremmel and some cursing cant make work!

Now that I look a the pics more and think about it, no dremmel and no cursing. All i have to do is tape up the breach end of the gun and drop a ball down the barrel. the breach IS the male adapter...after a fashion. I'm sure it will work though. I'll try tomorrow to shoot through 1in of the "shop board". I think I have a good shot at it. Starman do you ever run into a problem of tape bits building up and fouling your barrel?
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Unread postAuthor: starman » Thu Jan 22, 2009 11:58 pm

Combustion Monkey wrote:Starman do you ever run into a problem of tape bits building up and fouling your barrel?


Not in the least. The centers of the disks end up in blue bits out on the ground in front of the shooting. You just have to peel the "used" blue tape ring off of the male coupler and tape her up again. If anything, picking up the "blue bits" mess can be a little bit of a pain in the hiney if you have done a lot of shooting.

Keep a sharp pocket knife or utility knife and a small block of wood handy with which to trim the tape.
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Unread postAuthor: Combustion Monkey » Fri Jan 23, 2009 12:01 am

Sounds perfect! I'll try it tomorrow and see how it works. If it works as well as it should i'll post damage pics. Stay tuned!

Well it worked very well! Here is the proof.


Image

The entrance.

Image

The exit.

Image

I tried one more layer wich was not penetrated. But I think it will under better / warmer conditions.

Image

The front.

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The back.

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Unread postAuthor: starman » Sat Jan 24, 2009 4:38 am

Very nice indeed. Did you try the burst disk setup? I'm curious as to your thoughts on performance as a whole.
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Unread postAuthor: Combustion Monkey » Sat Jan 24, 2009 10:07 am

Yes it was done with the burst disk. Rather than rigging it onto my barrel camlock I just taped over the breach end of the barrel. I am very impressed with the results. I'll have to pick up some spuds and try it with them just for comparison. I don't think i'll use them often with spuds though due to the down time for retaping between shots.
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Unread postAuthor: starman » Sat Jan 24, 2009 4:40 pm

Combustion Monkey wrote:Yes it was done with the burst disk. Rather than rigging it onto my barrel camlock I just taped over the breach end of the barrel. I am very impressed with the results. I'll have to pick up some spuds and try it with them just for comparison. I don't think i'll use them often with spuds though due to the down time for retaping between shots.


I've found that shooting spuds with a burst disk is a good way to make potato salad... 8) The spud just can't stand up to the high pressure shock.

Go for a longer barrel and let the power build a little more slowly for intact spud shooting.
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Unread postAuthor: Ragnarok » Sat Jan 24, 2009 5:13 pm

starman wrote:I've found that shooting spuds with a burst disk is a good way to make potato salad... The spud just can't stand up to the high pressure shock.

That sounds odd to me, as I've fired spuds entirely intact at over 300 psi, with a piston valve that's no slouch.
I know a burst disk will result in the pressure reaching it's peak faster, but you're dealing with things of the order a quarter of that pressure, so the overall rate of pressure rise is almost certainly less than what I'm dealing with.

Soft stuff like grapes hasn't a chance of staying whole at anything like those pressures, but spuds hold together pretty well.
I suppose you are dealing with spuds that are relatively (compared to their diameter) shorter than what I'm firing, but I don't know how much difference that will make.

Perhaps it's the burst disk itself that's damaging the spuds when it breaks? Or maybe I've just had good luck with a cannon design that's able to keep spuds intact unusually well?
We can only really guess.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: Combustion Monkey » Sat Jan 24, 2009 5:45 pm

Oh and i have plenty of barrel :wink: . Four feet of internal then two 3.5ft sections that i can add externally.
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