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ME20H-41, by DYI

Built a hybrid cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: Lentamentalisk » Tue May 13, 2008 5:52 pm

So is the supersonic speed just an estimate? I completely believe it, but you have no solid proof of it I take it?
Also, how would one know if detonation did occur? (besides the obvious chamber flying in all directions, assuming that everything survived intact)
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Unread postAuthor: psycix » Tue May 13, 2008 5:55 pm

Im surprised that your camera didnt fell in the water using such a ghettopod near so near to it.
It looks like a slight burst of wind, or a 20X mix shockwave can easly blow it over. :lol:
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Unread postAuthor: DYI » Tue May 13, 2008 6:04 pm

Well, HGDT said that the 8x was 1270 fps with very conservative numbers, and 1340 fps with more realistic numbers. That, and the obvious sonic boom that was echoing around for a few seconds after the shot kind of convinced me. And really, when one considers that the speed of sound in the plasma in the chamber is over 3000 fps, Mach 1.1 or so muzzle velocities aren't really an amazing feat.

If the simulation said I was exceeding the SOS in the combustion gases I'd begin to doubt it, but at less than half the SOS, I couldn't see any real horrible, 200 fps inaccuracies arising.
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Unread postAuthor: Lentamentalisk » Tue May 13, 2008 6:10 pm

I say stick a chrony on there and see how fast it is really going at 20x, but make sure to mount it directly to the barrel, so that the kick doesn't make it shoot straight through your electronics. ^_^
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Unread postAuthor: SpudFarm » Wed May 14, 2008 6:54 am

oh noo that is one thing that gets me to get really angry!! i had no internet connection at the time and did not se this before now :evil:


SCH 40 seamed steel at 20x oxy/propane is total suicide if you stand next to it!

i bet i could have walked to you with my chrony to proof this!

really good someone is getting a "insanity badge"

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Unread postAuthor: drex » Sat May 24, 2008 11:36 am

ever thought about taking it up to a 24X mix? :twisted: :twisted: . or do you not have the burst discs or balls to take it up that high?
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Unread postAuthor: SpudFarm » Sat May 24, 2008 1:21 pm

hey i got a real shock today.
i only need 8 layers of aluminium foil for a 140psi shot :D

that means i have to use only 56.3 layers more to get a 10x :P
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Unread postAuthor: DYI » Sat May 24, 2008 6:27 pm

I could take it up to 24x... and I probably will next weekend. I believe that 128 layers of alu. foil should do the trick, but the peak pressure might demolish the whole thing. Needless to say, 24x would be the last shot of the day, one way or another :roll:

It must be kept in mind that 20x oxy/propane won't be as powerful as 20x air/propane, due to the difference in starting pressures. Unlike most solid fuels, the volume of combustion products is identical to the volume of fuel/oxidiser in oxygen/propane combustion, so pressure is only gained by heating. Pure oxy/propane gets hotter than air/propane, so for a given pre-ignition pressure, it will produce a higher peak pressure. However, with the same amount of fuel, air/fuel will produce a higher peak pressure, as the pre-ignition pressure is so much higher.

Come to think of it, there's probably a "sweet spot" oxidiser:inert gas ratio that could be used to balance higher pre-ignition pressures (and therefore higher combustion pressures) of diluted oxidiser mixes with the higher combustion temperatures (but also lower pre-ignition pressures) of concentrated oxidisers to get the highest performance for a given amount of fuel. I suspect we'd need some actual test data to find out for sure though *looks at Jimmy*.
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Unread postAuthor: drex » Fri May 30, 2008 12:53 am

my uncle was telling me about a tractor that he had that would spray water in to the chamber along with the fuel and air and when the combustion happened the water would turn in to steam giving the thing a huge boost in power. i wonder if you put some water in the thing woud it do the same? :?: :?:
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Unread postAuthor: psycix » Fri May 30, 2008 5:01 am

drex wrote:my uncle was telling me about a tractor that he had that would spray water in to the chamber along with the fuel and air and when the combustion happened the water would turn in to steam giving the thing a huge boost in power. i wonder if you put some water in the thing woud it do the same? :?: :?:

Yes Ive heard about that... going to search...

I found A wiki page!
http://en.wikipedia.org/wiki/Water_injection_%28engines%29

I also heard about a 6-stroke engine wich heats up using a normal fuel burn stroke, and then injects water the next stroke, wich turns to steam and gives another working stroke.

EDIT:
http://en.wikipedia.org/wiki/Crower_six_stroke
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Unread postAuthor: DYI » Mon Jun 23, 2008 5:22 pm

Update: added longer video.

Adding water might help, but I'll need to wait until I get a chrony to tell for sure, and that won't be for about 2 weeks yet. Wouldn't boiling the water be endothermic though? The question is, would the increased flow speed (and possibly increased volume?) of the gases make up for the heat loss to the water.
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Unread postAuthor: daxspudder » Mon Jun 23, 2008 5:53 pm

Hmm, in one of your many postings about this gun you said you were the only one with a video to prove a claim of 20x... but out of everything shown in your videos I didn't see one key piece of equipment, a compressor, only saw a large bike pump, which I'm pretty sure cant be pumped to 280(ish) psi... Not to be accusatory, but it doesn't seem that your video backs your claim... maybe a picture of a gauge reading to confirm? I really do want to believe this, so don't hate me for questioning you claim...
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Unread postAuthor: DYI » Mon Jun 23, 2008 6:24 pm

Hmm, in one of your many postings about this gun you said you were the only one with a video to prove a claim of 20x... but out of everything shown in your videos I didn't see one key piece of equipment, a compressor, only saw a large bike pump, which I'm pretty sure cant be pumped to 280(ish) psi... Not to be accusatory, but it doesn't seem that your video backs your claim... maybe a picture of a gauge reading to confirm? I really do want to believe this, so don't hate me for questioning you claim...


The careful observer will note that I never claimed to have used 20x air/fuel. I used oxygen for an oxidiser on those ones. The bottles in use, as well as spent bottles and spares, are easily visible in several of the clips. I'm doing a destructive test with 20x and higher air/fuel mixes as soon as I get the next generation hybrid done. For a given amount of fuel, it seems as though air/fuel mixes reach almost twice the pressure of oxy/fuel, although that's all just a guess until I can get my test set up in the summer.

You have every right to question my claims, and I realise that I should have backed them up more thoroughly. If it was my first post here, I probably would have taken video of the process of precharging up to 70psi with oxy/propane. I've never gone past 11x air/fuel, not because I'm not able to (I can easily get up to 20x air/fuel with my current resources), but because I don't want to destroy this thing yet.

If you're still having trouble believing me, I can do a test shot tomorrow afternoon and take video of the fueling and firing process.
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Unread postAuthor: daxspudder » Mon Jun 23, 2008 7:01 pm

n/m i feel totally stupid for not taking into account the ability of the tanks to pressurize the chamber :oops:
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Unread postAuthor: DYI » Mon Jun 23, 2008 7:12 pm

The regs for those little oxygen tanks only go up to 14.5 psi, but I heavily modified it. I now push down the diaphragm directly instead of using the dial and spring mechanism. The downside is that you can't use it for welding, but the upside is that it can go to at least 70psi on the output side (you have to fight pretty hard to get it there though).
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