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New Hybrid design

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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Unread postAuthor: boyce123 » Mon Jun 04, 2012 3:48 pm

the rear endcap shouldn't be a worry, as its just the end of the pilot chamber, i plan on reinforcing the back of the cap to take the impact of the piston. The front "cap" (a bell reducer to a bushing reducer) will at least be contained/covered by the 4" pvc then further heavily reinforced. The only safety issue i could see at a safe mix is the front cap blowing out, but it is containted, so the shrapnel would theoretically go forward.
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Unread postAuthor: MrCrowley » Mon Jun 04, 2012 5:01 pm

To carry on my suggestion from the SCH 40 vs ABS thread, what about fibre glassing the PVC and ignoring the other sleeving? It could be expensive and might be a bit difficult to do by yourself but I would think it would be easier to calculate its yield strength and such.
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Unread postAuthor: boyce123 » Mon Jun 04, 2012 5:52 pm

i was thinking of reinforcing the front end with fiberglass, would a layer of fiberglass be stronger than the extra sleeve of sch 40. i have already sleeved the inside with the copper pipe, the copper will also add a very good piston surface (over the irregular pvc).
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 05, 2012 12:50 am

boyce123 wrote:the copper will also add a very good piston surface (over the irregular pvc).


I've had the opposite experience, but perhaps the copper I was using had been abused.

boyce123 wrote:The only safety issue i could see at a safe mix is the front cap blowing out, but it is containted, so the shrapnel would theoretically go forward.


Welcome to the hybrid way of thinking :D

[youtube]http://www.youtube.com/watch?v=dQ2zB3PrpPo[/youtube]
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Unread postAuthor: boyce123 » Tue Jun 05, 2012 3:15 pm

is that schedual 80 pvc as the chamber...
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 05, 2012 11:30 pm

No idea what the US equivalent size is but it's roughly 1" OD and 3/4" ID PVC. The chamber holds up just fine even up to 8x:

[youtube]http://www.youtube.com/watch?v=w8MZ5aS2-JA[/youtube]

... what blew up was the cast epoxy breech :D
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Unread postAuthor: boyce123 » Wed Jun 06, 2012 9:57 pm

ah... it is schedual 80 (should hold up to around 700 psi), seems as if the epoxy should have held up...
what kind of pressures do you think your getting out of 8x with pipe that small

I have a single click bbq igniter, how many x's would this be able to function in, if it would be unreliable, i have access to cheap stun guns.

I currently have a 6 ft barrel, its kind of ridiculous for the size of the gun, i'm unfamiliar with hybrid ratios for chamber to barrel, would it cut much on permformance if i cut the barrel down a bit.
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 06, 2012 11:39 pm

boyce123 wrote:ah... it is schedual 80 (should hold up to around 700 psi), seems as if the epoxy should have held up...


The breech was unsupported and cast into a sheet copper structure that offered little in the way of additional strength. This means that while the cartridge itself held, once the pressure got into the breech area it couldn't take it.

what kind of pressures do you think your getting out of 8x with pipe that small


In this case I wasn't using a burst disk but a friction seal, so I doubt there was more than a couple of hundred psi in the chamber.

I have a single click bbq igniter, how many x's would this be able to function in, if it would be unreliable, i have access to cheap stun guns.


I've used piezo ignitors from cigarette lighters at up to 17x, the important thing is that the spark gap is really, really small, 0.5mm or less.

I currently have a 6 ft barrel, its kind of ridiculous for the size of the gun, i'm unfamiliar with hybrid ratios for chamber to barrel, would it cut much on permformance if i cut the barrel down a bit.


With the sort of pressure that hybrids generate, unless you have a microscopic chamber or working at very low mixes, it's hard to conceive of a barrel that is too long.
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