Posted: 05/12/2008 20:43 PM Post subject: ME20H-41, by DYI
Rear Brigadier
Joined: 07 Jul 2007 Posts: 2212 1308.29 Spud Bux
Miniature Experimental 20x Hybrid - 41mm
Nothing very exciting here, but due to its extreme affordability and ease of replacement (along with a hell of a lot of wire), I can test it up to its limits, which I haven't managed to reach so far, although I have gained some interesting insights along the way.
Specifications:
Chamber
Material: SCH 40 welded steel pipe, 150 psi rated malleable iron fittings
Volume: ~87ci
Configuration: SCTBDC style, with elbow on back for quick reloading and versatility
Fueling
My universal fuel meter, capable of up to 20x air/propane, or up to 24x oxygen/propane
Ignition
Ignition device: 3 camera flash capacitors (wired in parallel) discharged through a 1:100 winding ratio coil, for 33kV.
Spark gap: single central gap, ~0.5mm
Sparkplug: 1/2" epoxy filled brass nipple with two conductors, so that current never passes through chamber material
I've tried it at up to 20x oxy/propane, and I don't intend to try it any higher. Unlike most ridiculous claims, this one comes with video evidence.
Also, I have pictures. I had to make a new Photobucket account just to host them because my old one crapped out on me.
The whole thing, sans sparkplug (it got pwned by 20x)
The barrel, 1.5" ABS inside 3" ABS, with fiberglass filling the gap
The breach. The barrel extends so that it is flush with the sealing face of the union.
Our target barrel, 1/16" steel walls. The scale isn't quite apparent from this picture, but the barrel is over 8 feet high.
The 3" diameter hole in said target after the impact of a supersonic (~1300 fps) golfball core. The biggest fragments of the projectile after it impacted were roughly 1/4" across.
The GHETTOPOD (tm), with its proud creator Kevin, used to hold the camera for the 20x while we retreated to a safe distance behind 4 feet of stone.
A 64 layer alu. foil burst disk after 20x. I know it should have been thicker, but it was all we had left. With an estimated failure pressure of 1kpsi, it certainly wasn't a pushover, and the total combined thickness of the layers was over 1/8". The fact that there was no apparent detonation at 20x with an OXYGEN/PROPANE mix says something about our current knowledge of combustion, in my opinion.
can 150 psi fittings take that 20 x mix? if its safe, i feel stupid. i was about to buy 3000 psi rating fittings and pipe for a mini hybrid 10 times smaller than that.
good god, i don't think yelling fire in the hole is enough, you should get an air horn, i'm pretty sure you can hear the gun farther away than you could hear someone yelling
can 150 psi fittings take that 20 x mix? if its safe, i feel stupid. i was about to buy 3000 psi rating fittings and pipe for a mini hybrid 10 times smaller than that.
Not in the least! That is why they had the camera set up on a tripod, and they were behind 4 feet of stone.
150 psi rated fittings might be able to take it, but considering that the safety factor is dropped to roughly 1.05 (where 3 is safe, 2 is dubious, and 1.5 is "run like hell"), I wouldn't be anywhere near it when it was set off.
The sound is difficult to describe, really. You have to be there to understand it, but it sounds kind of weird because the noise is somewhat directed until it starts echoing. Apparently, on the first supersonic shot at 8x (before the cameraman cleared the area along with me at 12x), the sound made his ears ring from 20 feet away, almost directly behind the launcher.
The sound of our warnings before the dangerous shots would carry far enough to warn any unlucky bystanders to take cover immediately.
On the only 20x of the day, we were 150 feet away, behind a 4' thick stone piling.
That is very nice. That cannon actually mimicked my friend's "magic dust" cannon, which slides backwards about 10 feet when fired (loaded with lead shot and a good quarter cup or so of "dust"), a good feat for a "magic cannon" which weighs a good 130 pounds due to the lead used in it's construction.
You can see this "magical device" in time lapse 0:08 - 0:14 of this movie.
But, anyways, good job. Certainly a first: 20x oxy/propane. Hope you can keep pushing the limit.
Congratulations, seems as though you have made a monster. Way cool. Supersonic BB's are one thing, but golfballs (at least the core), that's insane.
On another note, I can totally see someone saying "nice gun, but look at my awesome advanced combustion!" and then adding a link to their spray and pray. That's more than a little bit random, I guess big booms get me all worked up.
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