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Hybrid WIP.

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 WIP.

Unread postAuthor: SpeedyFerrite » Sat Mar 29, 2008 8:37 am

I'm building a hybrid that's 35 mm in diameter with 5 mm thick walls, The thing is aluminium, what will be the highest mix I could use safely?
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Unread postAuthor: SpudFarm » Sat Mar 29, 2008 8:41 am

8 or 9x...
5mm thick walls is really thick for steel but i don't know about alu..
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Unread postAuthor: bigbob12345 » Sat Mar 29, 2008 8:48 am

Ill say 12-13x but dont quote me on that
5mm is quite thick, even for aluminum.
I mean look at copper, thats probably not even 1mm thick. Aluminum is a little bit softer than copper but a 5mm wall of aluminum will hold at least three times as much pressure safely.
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Unread postAuthor: SpudFarm » Sat Mar 29, 2008 8:51 am

AND copper is rated REALLY high..

i think he wants a good safety margine...
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Unread postAuthor: DYI » Sat Mar 29, 2008 9:45 am

1" copper pipe with walls about 1mm thick is rated for ~1 000 psi. This will be able to take higher mixes than a conventional air compressor will be able to fuel it to. I'm assuming you're machining it out of bar stock?
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Unread postAuthor: SpeedyFerrite » Sat Mar 29, 2008 11:09 am

DYI wrote:1" copper pipe with walls about 1mm thick is rated for ~1 000 psi. This will be able to take higher mixes than a conventional air compressor will be able to fuel it to. I'm assuming you're machining it out of bar stock?


No, it's piping, but i did machine the fittings. :)

I'll have to install the spark plug tomorow and it'll be good to go.

*edit* what about DDT?
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Unread postAuthor: SpudFarm » Sat Mar 29, 2008 11:19 am

how long is your chamber?
you need to have a really long chamber for DDT
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Unread postAuthor: Lentamentalisk » Sat Mar 29, 2008 12:02 pm

your pipe is almost never what you have to worry about pressure wise. The fittings are always much weaker than the pipe. For example, threaded unions at the 2" size can generally only take around 200psi, while their corresponding pipe can take well into the thousands.
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Unread postAuthor: SpeedyFerrite » Sat Mar 29, 2008 12:13 pm

Lentamentalisk wrote:your pipe is almost never what you have to worry about pressure wise. The fittings are always much weaker than the pipe. For example, threaded unions at the 2" size can generally only take around 200psi, while their corresponding pipe can take well into the thousands.


I machined the fittings from solid aluminium.
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Unread postAuthor: Lentamentalisk » Sat Mar 29, 2008 12:20 pm

you should be very well covered on that account...
Cant wait to see it.
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Unread postAuthor: SpeedyFerrite » Sat Mar 29, 2008 2:03 pm

Picture of it right now.
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Unread postAuthor: bigbob12345 » Sat Mar 29, 2008 2:10 pm

oh its low diameter
that makes things even better, i was assuming thjat it was 2in or something.
Im going to stick with my previous opinion of 12-13x maximum although it could probably even take DDT a couple times
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Unread postAuthor: DYI » Sat Mar 29, 2008 2:46 pm

Low diameter actually shortens the DDT runup distance, making it more dangerous. It should be able to survive a DDT, but I wouldn't be too confident in its safety afterward. And the ball valve would obviously need to be replaced if a DDT did occur.

For example, threaded unions at the 2" size can generally only take around 200psi


Where did you get that figure from? How many tests were done in the study that came to this conclusion? If that number's right, I either have an extraordinarily strong union, or a metric assload of good luck, because I use them at 450psi regularly on the SCTBDC.

@SpeedyFerrite: If you can find the fatigue yield strength of your aluminum alloy, you can use Barlow's formula to get an approximate static burst pressure (shock would lower that number).
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Unread postAuthor: bigbob12345 » Sat Mar 29, 2008 2:50 pm

DYI wrote:Low diameter actually shortens the DDT runup distance, making it more dangerous.


yes I realise that but this isnt nearly long enough for there to be any real danger of 12-13x mixes. If it was twice as long i would say otherwise
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Unread postAuthor: sniperjosh » Sun Mar 30, 2008 6:14 am

Looks awesome, what FPS does it pump out? I think your barrel should be a lot longer for that chamber setup.
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