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Worlds Largest Combustion PVC Cannon?

A place to ask general spud cannon related questions.
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Unread postAuthor: psycix » Sun Oct 12, 2008 5:40 pm

Sweet!
Large bore fun!

A few things:
-Thought of adding more spark gaps? Surely increases performance in large chambers.
-And:
Dude! ADD A FAN! Seriously!
It may increase the velocity by a freaking 20-50%.
It mixes, it vents AND induces turbulence for faster burn rates.
If ANYTHING is worth the effort, then a fan comes at the first place!
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Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!

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Unread postAuthor: Ragnarok » Sun Oct 12, 2008 5:58 pm

Engineer87 wrote:but we found out that the gas sinks

This is part of what the chamber fan is designed to fix. It's not exactly hard to put one in place, I think it could well be worth your time.

@mrbadexample: Big bore cannons always tend to have lowish muzzle velocities, because the forces available scale with the square of the bore, but the projectile size tends to scale with the cube, so as a rough rule, a doubling in bore size tends to drop by 30% unless the barrel is lengthened to compensate, and that's only practical so far.

Personally, I'd guestimate this cannon to have a potential muzzle energy of a good 6,000 ft-lbs if it had a tight fitting projectile and the aforementioned chamber fan, and that's nothing to sniff at.

At a rough guess, the cannon is probably generating at least half of that figure as it is. You might not realise it, but I reckon there was at least 3 kg of wood loaded in the cannon in one of the shots on that video. Guessing a range, and working back to a muzzle velocity, I'd say there was at least 3,000 or 4,000 ft lbs there, and likely more - it may look slow, but the sheer weight of the projectile (which is evidently more than you realise) means it's making a lot of energy.

And it won't kick far, because it's heavy.

You might not think much of it, but I can tell you it's a beast.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: mrbadexample » Sun Oct 12, 2008 6:26 pm

a huge barrel that tosses towels... hmmmm... now where am i? i thought "spudfiles".... seems i have drifted into the "towel zone".

my bad... let's all toss towels!

ok, we'll rename this website "towelfiles", after all, it's about how well you can shoot a towel...
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Unread postAuthor: Engineer87 » Sun Oct 12, 2008 6:42 pm

Ragnarok wrote:
Engineer87 wrote:but we found out that the gas sinks

This is part of what the chamber fan is designed to fix. It's not exactly hard to put one in place, I think it could well be worth your time.

@mrbadexample: Big bore cannons always tend to have lowish muzzle velocities, because the forces available scale with the square of the bore, but the projectile size tends to scale with the cube, so as a rough rule, a doubling in bore size tends to drop by 30% unless the barrel is lengthened to compensate, and that's only practical so far.

Personally, I'd guestimate this cannon to have a potential muzzle energy of a good 6,000 ft-lbs if it had a tight fitting projectile and the aforementioned chamber fan, and that's nothing to sniff at.

At a rough guess, the cannon is probably generating at least half of that figure as it is. You might not realise it, but I reckon there was at least 3 kg of wood loaded in the cannon in one of the shots on that video. Guessing a range, and working back to a muzzle velocity, I'd say there was at least 3,000 or 4,000 ft lbs there, and likely more - it may look slow, but the sheer weight of the projectile (which is evidently more than you realise) means it's making a lot of energy.

And it won't kick far, because it's heavy.

You might not think much of it, but I can tell you it's a beast.


My worries with doing anything that upps the power comes from the idea that it's made of sch 40 pvc, and I don't want the cap to blow off again. I'm going to add is those hose clamps to reinforce the adapter, but I'm still unsure. If I do everything you said right now and actually get double the power, well i don't know.
My uncle hosts a father son potato gun build/shoot off, and the purpose of this gun is to impress people, most of which have never even heard of a gun this big. It's gonna do that, and upping the power anymore is only going to make it more dangerous. But I do appreciate your tips and I will ipmlement them on my mapp gas metered tennis ball launcher, damn does it shoo tennis balls high, I can't imagine anymore power on that thing.



P.S. mrbadexample,
Your a douchebag.
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Unread postAuthor: jook13 » Sun Oct 12, 2008 6:52 pm

P.S. mrbadexample,
Your a douchebag.



hahaha.. it may be unappropriate but its funny..
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Unread postAuthor: Ragnarok » Sun Oct 12, 2008 6:54 pm

mrbadexample wrote:ok, we'll rename this website "towelfiles", after all, it's about how well you can shoot a towel...

Yes, because of course every cannon on this site shoots spuds - like hell they do. There are paintball cannons, BB guns, marble launchers, basketball cannons...

Engineer87 has come on here with a perfectly legitimate cannon, and you seem to have the (false) idea that you have unlimited right to slag it off - if he used a towel as wadding, that's fine. Many people use rags in smaller cannons, so scaling up the idea is only sensible.

Currently, your user name seems apt.

Engineer87 wrote:If I do everything you said right now and actually get double the power

That 6,000 ft-lbs is a best case scenario with the right projectile and everything.

Going to there from a situation where you're generating 4,000 where you're not dealing in absolutes won't require double strain on parts.

Just a tighter fitting projectile with no air gaps would make a difference on it's own with minimal increased stress. The chamber fan will increase internal pressures by a small amount, but not so much I would be fretting.

However, your concerns are perfectly sensible, so don't let me push you into it if you don't want to.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: DYI » Sun Oct 12, 2008 7:05 pm

My worries with doing anything that upps the power comes from the idea that it's made of sch 40 pvc, and I don't want the cap to blow off again. I'm going to add is those hose clamps to reinforce the adapter, but I'm still unsure. If I do everything you said right now and actually get double the power, well i don't know.
My uncle hosts a father son potato gun build/shoot off, and the purpose of this gun is to impress people, most of which have never even heard of a gun this big. It's gonna do that, and upping the power anymore is only going to make it more dangerous. But I do appreciate your tips and I will ipmlement them on my mapp gas metered tennis ball launcher, damn does it shoo tennis balls high, I can't imagine anymore power on that thing.


If you're worried about increased power being a problem (a sentiment that I've never personally experienced :roll: ), then just turn off the fan before you fire. It will boost power only slightly ( the combustion will be more consistent throughout the entire, monstrous chamber, not a whole lot more forceful), but instead of trying to ignite it for several seconds in some cases, ignition will as soon as the first arc fires.

If those parts you have are SDR 26 or better, you have nothing to worry about from propane/air mixes, no matter what you do to boost the power (short of detonating the mix, of course).

I'm contemplating a big-bore combustion right now, and I have to say that I admire the expense necessary to make one this big from parts that you actually bought. On the other hand, I can't understand the reluctance to get more performance out of it - why build something on this scale, and then intentionally use it at less than its full potential?
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Unread postAuthor: starman » Sun Oct 12, 2008 7:18 pm

mrbadexample wrote:a huge barrel that tosses towels... hmmmm... now where am i? i thought "spudfiles".... seems i have drifted into the "towel zone".

my bad... let's all toss towels!

ok, we'll rename this website "towelfiles", after all, it's about how well you can shoot a towel...


I saw large chunks of wood dropped in on the back side of those towels. They aren't just shooting towels. They are SMARTLY using towels as a sabot to seal the barrel and chamber. What else would YOU suggest using to do that job MrBad?

MrBad you should probably stop going down the trail you are on here. It isn't a winner for you.
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Unread postAuthor: mrbadexample » Sun Oct 12, 2008 8:50 pm

Engineer87 wrote:
Ragnarok wrote:
Engineer87 wrote:but we found out that the gas sinks


Personally, I'd guestimate this cannon to have a potential muzzle energy of a good 6,000 ft-lbs if it had a tight fitting projectile and the aforementioned chamber fan, and that's nothing to sniff at.


You might not think much of it, but I can tell you it's a beast.


6,000ft-lbs?!?!?!? i'll have what you're smoking bud!!! sched 40, at 8 inches? hell, you're lucky to get 100 PSI. i've seen some of the postings here, "children".

you guys are babes in the woods, 6000 ft-lbs would make a crater you couldn't dig out of! and certainly schedule 40 is not capable of 6000 ft/lb .
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Unread postAuthor: MrCrowley » Sun Oct 12, 2008 8:57 pm

mrbadexample wrote:
Ragnarok wrote:
Engineer87 wrote:but we found out that the gas sinks


Personally, I'd guestimate this cannon to have a potential muzzle energy of a good 6,000 ft-lbs if it had a tight fitting projectile and the aforementioned chamber fan, and that's nothing to sniff at.


You might not think much of it, but I can tell you it's a beast.


6,000ft-lbs?!?!?!? i'll have what you're smoking bud!!! sched 40, at 8 inches? hell, you're lucky to get 100 PSI. i've seen some of the postings here, "children".

you guys are babes in the woods, 6000 ft-lbs would make a crater you couldn't dig out of! and certainly schedule 40 is not capable of 6000 ft/lb .

Obviously, you have no idea what you are talking about. SCH 40 has nothing to do with ft/lbs.

hell, you're lucky to get 100 PSI.

He's lucky to get 100psi? Hmm i'm pretty certain that would be impossible with the cannons current setup. :roll:

You have absolutely no clue to what you are saying. I recommend you stop talking out of your ass.
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Unread postAuthor: LikimysCrotchus5 » Sun Oct 12, 2008 9:02 pm

He can get 100 psi out of his combustion, at his peak pressure maybe, but if he had a better setup, then he could.

I suggest that you dont make any accusations without good reasoning and examples to support them.
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Unread postAuthor: MrCrowley » Sun Oct 12, 2008 9:04 pm

I thought even with MAPP gas and perfect metering, combustions top out at ~80PSI?
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Unread postAuthor: DYI » Sun Oct 12, 2008 9:36 pm

6,000ft-lbs?!?!?!? i'll have what you're smoking bud!!! sched 40, at 8 inches? hell, you're lucky to get 100 PSI. i've seen some of the postings here, "children".

you guys are babes in the woods, 6000 ft-lbs would make a crater you couldn't dig out of! and certainly schedule 40 is not capable of 6000 ft/lb .


Judging by your posts today, I'm hoping that either:
a) your account got hijacked by a malicious sibling, or something similar
b) you're high as a kite
OR
c) both

For God's sake, tell me it's C :P
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Unread postAuthor: rp181 » Sun Oct 12, 2008 10:08 pm

even is the pressure is low, its a large area. Its pressure per square inch for a reason. 100 psi in a .5in barrel is less then 20 psi in a 10in barrel.

What a fitting username :roll:
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Unread postAuthor: LikimysCrotchus5 » Sun Oct 12, 2008 11:22 pm

MrCrowley wrote:I thought even with MAPP gas and perfect metering, combustions top out at ~80PSI?


Well i remember reading a combustion that was made by DR, and it used a sprinkler valve, which from what i read, said it takes 125 psi to open and he successfully did it.

I am pretty sure that the peak pressure can pass 80 psi.
jimmy101 wrote: The dial pressure gauge spikes to somewhere near midscale (100 PSIG) and then immediately drops back down to zero.


but that was in a closed chamber so, i can really be sure then about the differences.

rp181 wrote:Its pressure per square inch for a reason.

I think you mean pounds per square inch?

:roll:
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