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Hybrid Questions

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Hybrid Questions

Unread postAuthor: Modderxtrordanare » Thu Jul 12, 2007 6:58 pm

I have a few questions I need answered before I go and finish my hybrid.

I already have the genII tank for it done, which consists of 50" ir 2" SCH80 PVC. But I need to know how long a barrel I should cut for my hybrid, since C:B ratios are different for hybrids. (.3:1 for a 2x mix?)

The actual ignition chamber is 2 feet of 2" SCH80, and I wan't the barrel to be 1.5" sch40 pipe but I don't know how long to cut it to. Also, should I even use sch40 for a hybrid's barrel, or is that dangerous for the barrel?

Next, for a 2x mix, would one layer of a soda can work for a burst disk? Would a layer of milk jug work better? Something better?

Thanks in advance. :)
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Unread postAuthor: spudthug » Thu Jul 12, 2007 8:27 pm

for 4x mix its .3:1 i forget the other ones but its on here somewhere..

you can use sch 40 for a hybrid barrel and it isnt dangerous..people use golfball barrels and those are like sdr 21 (really thin..)

for 2x i use milk jugs..for 4x i use soda cans
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Last edited by spudthug on Fri Jul 13, 2007 7:46 am, edited 1 time in total.
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Unread postAuthor: Modderxtrordanare » Thu Jul 12, 2007 8:43 pm

spudthug wrote:for 4x mix its .3:1 i forget the other ones but its on here somewhere..

you can use sch 40 for a hybrid barrel and it isnt dangerous..people use golfball barrels and those are like sdr 21 (half of sch 40)

for 2x i use milk jugs..for 4x i use soda cans


Well I have a union on my filling chamber for saftey reasons as well. I just wanted to know whats a good material to keep that all sealed up, but if somehow it does ignite in there, the disk will go and I wont die.


SDR is a measurement of pressure and SCH isn't, just by the way. Also, I've seen a person who used a sch40 barrel on their hybrid (I think) and it blew. I belive it was "The JAUSH" cannon.
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Unread postAuthor: DYI » Thu Jul 12, 2007 8:57 pm

Yes, it was, but the JAUSH was running a 7x mix when that happened. I think that SCH40 barrels are usually fine for hybrids running mixes below 4x, and they have been used succesfully on many PVC hybrids.
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Unread postAuthor: beebs111 » Thu Jul 12, 2007 9:05 pm

hell, i think it was DR that preferred to use Sch 40 for all of his hybrid components. on my sch 40 mini hybrid i use a 4x layered Al foil for 2x mixes, works like a charm.
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Unread postAuthor: BC Pneumatics » Thu Jul 12, 2007 9:40 pm

David didn't 'prefer' sch 40, but his first hybrid was made from it. (4")
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Unread postAuthor: Scotty » Fri Jul 13, 2007 7:30 am

I think you should cut your barrel as long is as practical.

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Unread postAuthor: spudthug » Fri Jul 13, 2007 7:48 am

SDR is a measurement of pressure and SCH isn't


yes but they use wall thickness and pipe diameter to figure out that pressure rating..and i never said sdr wasnt a pressure rating..

Many PE pipe manufacturers use the "Standard Dimension Ratio" - SDR - method of rating pressure piping. The SDR is the ratio of pipe diameter to wall thickness and the SDR can be expressed as

SDR = D / s (1)

where

D = pipe outside diameter (mm)

s = pipe wall thickness (mm)

A SDR 11 means that the outside diameter - D - of the pipe is eleven times the thickness - s - of the wall.

with a high SDR ratio the pipe wall is thin compared to the pipe diameter
with a low SDR ratio the pipe wall is thick compared to the pipe diameter
As a consequence a high SDR pipe has a low-pressure rating and low SDR pipe has a high-pressure rating.
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Unread postAuthor: sniperjosh » Fri Jul 13, 2007 8:08 am

sch40 barrel should be fine with your setup (assuming ur main use is 2x???), what mixes are u planning to go to?? For your chamber with sch80 PVC 2" , i would glue straight fittings over the entire chamber, to give you double the wall thickness since it is pvc (if ur thinking about 3x).

For testing the JAUSH im using sch40 barrels still, ill let you guys know how they hold up, so far they have held up to 6x with no probs, i think they will fatigue over time though. I have lacked the time the past few days to do anythign with it, though :(
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Unread postAuthor: Modderxtrordanare » Fri Jul 13, 2007 9:03 am

spudthug wrote:yes but they use wall thickness and pipe diameter to figure out that pressure rating..and i never said sdr wasnt a pressure rating..

[Explanation of SDR]


I know how they find SDR ratings, I was merely remarking upon the fact that you were comparing the two. They're like apples and oranges my friend.

Scotty wrote:I think you should cut your barrel as long is as practical.

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If I were to cut it to a length I thought "looked good" and wasn't too long, I wouldn't have a proper C:B ratio, and I would be losing preformance due to that fact. Plus a bigass cannon is always fun to brag about. :lol:

sniperjosh wrote:sch40 barrel should be fine with your setup (assuming ur main use is 2x???), what mixes are u planning to go to?? For your chamber with sch80 PVC 2" , i would glue straight fittings over the entire chamber, to give you double the wall thickness since it is pvc (if ur thinking about 3x).


That would be simple in theory, but to actually slide enough couplings over my chamber and get them in place before the glue sets is a hard feat. The couplings around here have little rings inside that I'd have to bore out, and even then they would all be a tight fit.

Also, I only plan on using 2x mixes here, mainly due to sheer laziness. I really don't feel like recalculating a meter pipe, or re-building the filling chamber bigger. I might cut down on the chamber a little bit, in an attempt to get around a 2.5x mix. That would be my limit for PVC, any more, and I can't trust it as far as I can throw it.

sniperjosh wrote:For testing the JAUSH im using sch40 barrels still, ill let you guys know how they hold up, so far they have held up to 6x with no probs, i think they will fatigue over time though. I have lacked the time the past few days to do anythign with it, though :(


6x mix = :love7:
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Unread postAuthor: noname » Fri Jul 13, 2007 10:23 am

A Sch 40 barrel will be fine. As for length, just get a 10 foot piece of 1 1/2" Sch 40 (that's what I did) and chop it down if it doesn't work well.
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Unread postAuthor: spudthug » Fri Jul 13, 2007 10:29 am

you can go up to 4x with sch 80 dude...no problem..there arent many metal hybrids..most of them are 2" sch 80 chambers to...
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Unread postAuthor: noname » Fri Jul 13, 2007 10:36 am

Spudthug, maybe you can take Sch 80 PVC to 4x, maybe you can't. I've had 3/4" Sch 40 PVC (rated to 480 psi @ 73* F) explode at 140 psi. It was about 80 degrees, and there were no imperfections in the pipe.

The lesson? crap happens, don't try your luck with unsafe stuff.

I would never take any of my PVC hybrids to 4x for the same matter.
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Unread postAuthor: sniperjosh » Fri Jul 13, 2007 6:24 pm

Modder, you dont need to change ur meter pipe size, just put a regulator before the meter pipe??

as for the 6x mix w/ sch40, let me be the ginuea pig - dont go getting hurt! :)

Yeh, i thought you were planning on only using 2x by what you said. Im not sure if you will be able to resist curiosity though, after you fire off a few 2x shots :wink: Just play safe :D
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