Question


Postby markfh11q » Sat Dec 30, 2006 7:00 am

Just a simple question for you guys. I'm building my first full-sized hybrid, (my other can be considered a mini, if you will), and I'd like to know how much power can be expected from a 2x14" SCH-80 chamber connected to a sleeved 5' long SDR-21 golfball barrel. I'm not to good at calculating ballistic performance all my my lonesome, but I modeled it in GGDT and got <a HREF="http://i10.photobucket.com/albums/a123/markfh11q/screenshot.png">this</A>. I'm sure I'm not accounting for something, though, as that number's kind of high.

I'd just like somebody to double-check me on this and provide any performance buffers there may be.

Thanks.

EDIT: GGDT also says I can break the sound barrier, (where I live), with a 4x/4 atm mix and a 10' barrel. If so... cool.8) Don't know where I'm gonna get a 10' stick of SCH-80 though. Had to order a 5' stick off McMaster to even get SCH-80 in the first place!:evil:The SDR-21 is no problem, though. I've already got ten feet, (cut into two 5' sections), in the closet. Come to find out the hardware store down the road has it for $0.56 a foot!:| I shoulda asked a LONG time ago.

EDIT II: No, this stuff can't be right, because configuring it to a 1x/1 atm mix yields very high results for your typical combustion at almost a .289:1 ratio. Any ideas?
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Postby Velocity » Sat Dec 30, 2006 11:33 am

For the barrel, just buy two 2"x60" lengths of SCH 80 pipe off mcmaster, and connect them together by using a coupling. Then slide the 1.5"x120" SDR-21 barrel inside that. Because the golfball is not touching the SCH 80 part at any time, the seam shouldn't matter.
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Postby boilingleadbath » Sat Dec 30, 2006 1:27 pm

I've not found a reliable way to model combustion spudgun preformance using he GGDT.

However, as a wild geuss, one might try hacking EVBEC.
I don't know if it'll work, but here is my idea:

1)We know the (1x) spudgun's preformance in atmosphere - it's simple to calculate preformance in a vacume (simple energy calculations).
2)We then have the spudgun's preformance in terms of absolute pressure. Multiply the energy output by the mix, and you have your answear.
3)We simply recalculate the preformance in atmosphere.

Done... one half-assed aproximation of hybrid preformance using EVBEC.
(problem is that this requires doing calculations in real energy units... which EVBEC currently isn't set up for - so it's a bit more work than what I presented it as... but if you guys think it's halfway viable, I'll be happy to implement it.)
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Postby BigBang » Sat Dec 30, 2006 7:34 pm

I don't think GGDT will help you model the performance of a combustion gun. I went to great lengths to model Latke's MiniL1 gun about a year ago. I just got garbage. Take a look at my post in <a href="http://localhost/forums/viewtopic.php?t=14713">THIS</a> thread, about 2/3 of the way down on the first page. A link to my GGDT file is there too.
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Postby harmon12407 » Mon Jan 08, 2007 9:07 pm

i went to an industrial supply store for my sch80. they had 20 foot sections and i had to ask for a 10 footer! also, DR made a hybrid (believe this was his gen II) similar to this size and put a golfball clean through a 2x6. that should answer any questions about power..
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