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A place to ask general spud cannon related questions.
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Unread postAuthor: brogdenlaxmiddie » Sat Feb 14, 2009 11:00 pm

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Unread postAuthor: MrCrowley » Sat Feb 14, 2009 11:21 pm

What size steel plates should I get put on the ends?

I'd have no idea, but I would imagine something around 1/4" thick.

What would the recommended Mix be?

Depends on the lowest rated part of the cannon, it should probably be able to go in excess of 20x safely.

What would you use for combustible fuel? Propane or MAPP? I'm thinking propane because I can get large quantities for cheaper.

You just answered your own question there. MAPP is better, but if it's easier and cheaper to get propane, go for it.

Ignition systems?

Stun gun?

What would you use for a barrel? PVC or Al or Steel?

I'd go with Al or steel. D_Hall listed some nice metal tubes from McMaster suitable for golfballs in a topic recently. Though you probably want something a little larger then that as well :wink:

Edit: just realised you're talking about 10" diameter pipe..guess it pays to read everything before posting :oops:
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Unread postAuthor: brogdenlaxmiddie » Sat Feb 14, 2009 11:23 pm

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Re: That giant steel pipe I have just laying in the backyard

Unread postAuthor: D_Hall » Sun Feb 15, 2009 12:14 am

brogdenlaxmiddie wrote:-What size steel plates should I get put on the ends? (in terms of thickness)

Really, you shouldn't use steel plates and should instead invest in some bullnoses. But if you MUST use steel... Remember that at 10" diameter you've got 78 in^2 of area to deal with. Even with a simple combustion, that means you're potentially talking about 7,800 pounds of force. This is NOT something for a thin flat plate. Without doing any calculations, I'm thinking I wouldn't go for anything less than 1" plate (if I was going for plate and not a bullnose)....and honestly, even that would make me squirm a bit since we're talking about a hybrid. Suffice to say that the geometry of a flat plate absolutely SUCKS for pressure vessel applications.

-What would the recommended Mix be? (in terms of 'X')

Assuming you're got sch 40 pipe (you never say), your wall thickness is 0.365". Roughly speaking, that implies an *optimistic* failure at about 2500 psi. Using a 5:1 safety margin, that means you shouldn't push it past 500 psi. In other words, about 5X.

-What would you use for a barrel? PVC or Al or Steel?

Steel. It's not like you're gonna move this thing around easily anyways. A bit more weight isn't gonna make any difference. Steel is robust and cheap (compared to aluminum).
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Last edited by D_Hall on Sun Feb 15, 2009 12:16 am, edited 1 time in total.
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Unread postAuthor: starman » Sun Feb 15, 2009 12:16 am

This has the potential of being a very high energy cannon...and large scale.

Just running some practical numbers through HGDT...assumes
- a 10" x 24" chamber or 1885 cubic inches
- 3" x 120" barrel
- c:b = 2.2:1
- 3X mix
- 200 psi 3" burst disk
- 16 oz, 3" projectile (veggie can)
=
931 ft/sec velocity
13473 ft*lb energy
~265 psi peak barrel and chamber pressure

Try to find rounded end caps you can weld on the chamber ends, same gauge as your pipe...may not be easy to find. Getting a 200 psi, 3" burst disk may be your biggest challenge and may even require you to go down to a 2" barrel for practicality sake. I would recommend a trailered or truck bed artillery mount of some sort. Yeah propane by the BBQ size tank.

Other than D_Hall's secret monstrosity, Killjoy's FEAR is a something you should study...but you probably already knew that.... :wink:
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Unread postAuthor: brogdenlaxmiddie » Sun Feb 15, 2009 12:19 am

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Unread postAuthor: starman » Sun Feb 15, 2009 12:24 am

brogdenlaxmiddie wrote:The highest air pressure that I could get would be 105 PSI or air....


You mean for burst disk testing? You would only need 30 psi to load up to 3x. Did you have your eyes set on something larger than 3x mix?
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Unread postAuthor: brogdenlaxmiddie » Sun Feb 15, 2009 12:26 am

Not specifically, but I'm just giving some info about what I have to work with. I might one day make a high mix small hybrid rifle or something but thats far off in the future.
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Unread postAuthor: starman » Sun Feb 15, 2009 12:35 am

OK. You're just not going to need high X mixes with this huge chamber...available energy will be relatively massive at low mixes even with the sawed down 24" length of 10" pipe I threw out above.
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Unread postAuthor: brogdenlaxmiddie » Sun Feb 15, 2009 12:36 am

Those measures were with only 24" of the chamber????
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Unread postAuthor: starman » Sun Feb 15, 2009 12:47 am

Yup. Assuming everything else equal, going up to a 6' chamber gains you practically no projectile performance ....but massive wasted power in heat and noise behind the projectile.
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Unread postAuthor: brogdenlaxmiddie » Sun Feb 15, 2009 12:49 am

Noise is a necessity :)
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Unread postAuthor: starman » Sun Feb 15, 2009 1:38 am

Oh you'll have plenty of that with the 24".. 8) There's still a BUNCH of energy in that shot that isn't being tapped. If you were to double your barrel to 240" (20 ft) and all other things being equal, you could extract 20578 ft*lbs of energy and 1151 ft/sec velocity, theoritical supersonic veggies... :shock:

If you haven't installed HGDT yet, you should give it a whirl.
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Unread postAuthor: brogdenlaxmiddie » Sun Feb 15, 2009 1:47 am

Hmmmm.... I think it would be really hard for a potato to withstand supersonic speeds..... I'm thinking more about launching old propane tanks with cement in them :)
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Unread postAuthor: starman » Sun Feb 15, 2009 1:52 am

brogdenlaxmiddie wrote:Hmmmm.... I think it would be really hard for a potato to withstand supersonic speeds..... I'm thinking more about launching old propane tanks with cement in them :)


Oh you're waayyyyy beyond tater launching here....unless you're interested in tater mist... :wink: I was talking about veggies in the can.

Old propane tanks are more like it although concrete may be unnecessarily difficult to work with. How about just sand or water?

Oh and...if you wanted to shoot golf balls, with a 120" barrel you're talking well into supersonic, maybe mach 1.2 - 1.4.
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