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strange hybrid reading

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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strange hybrid reading

Unread postAuthor: SpudFarm » Mon Jul 07, 2008 12:27 pm

hey i got Larda to fire every time now. (it is from now on called UPGBH10x)
on 3x it had a average from 650fps to 1400fps depending on the disk.
i did the last shot and prepared to pack it all together to tell about the normal readings i got...
i used a 32layer burst disk and 3x and pressed the trigger. it was much louder than the other shots and i walked there with the camera (yes i got it on tape) to look at the chrony and i could not belive what i saw! 4420fps! yes that is mach four!

what i wonder is what could have caused this extremely fast shot!

BTW the first plate on the video is 2mm and the last one is 3mm and it tore itself a good 15"


[youtube]http://youtube.com/watch?v=kU7OC3B_OMQ[/youtube]

the plate belives it can fly :)

BTW i am going to dig myself in the ground in the backround there and try to find the ball


ohh one detail is the change of a spark plug to get it to work every time. it now has a 0.25mm gap at the very back of the chamber.

little EDIT: the crony shows M/S
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Unread postAuthor: jonnyboy » Mon Jul 07, 2008 12:40 pm

Very exciting!

Wish I had a hybrid. :(
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Unread postAuthor: Hotwired » Mon Jul 07, 2008 12:44 pm

Whoo, that is an abnormally high reading. Precious few bullets fire that fast. In fact I'm not seeing any commercial bullets that go faster than that.

Has it happened again?
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Unread postAuthor: SpudFarm » Mon Jul 07, 2008 12:47 pm

DYI to spudfarm on MSN: if you can't replicate the effect, you'll get flamed for posting about it


i will try tomorrow at a little higher mixes and see if i can get it to happend again.
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Unread postAuthor: DYI » Mon Jul 07, 2008 12:58 pm

If your normal shots are 400 m/s, and this is over 1200 m/s, that's about 10 times the energy.

What we reall have to figure out is this: is there even enough potential energy in the combustion to make this possible? *looks at Jimmy/SB15/BLB*
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Unread postAuthor: SpudFarm » Mon Jul 07, 2008 1:19 pm

i am going to try to put the chrony longer from the muzzle and put it all up the same way.

it should not have been the bits of the burst disk because it was loads of foil in the chamber after that shot.
it could not have been passby gases either because the ball compresses and form a 100% seal
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Unread postAuthor: jimmy101 » Mon Jul 07, 2008 1:20 pm

DYI wrote:If your normal shots are 400 m/s, and this is over 1200 m/s, that's about 10 times the energy.

What we reall have to figure out is this: is there even enough potential energy in the combustion to make this possible? *looks at Jimmy/SB15/BLB*

As cool as it would be to get a hybrid firing this fast I don't think it is very likely.

Like DYI said, that's 10 times as much kinetic energy as most shots from the gun. UPGBH10x is a big-ass gun but ~Mach 4 still seems unlikely. The energy in the chamber is probably still less than in a typical rifle cartridge.

To figure out if it's even remotely possible we need the chamber volume, mix, barrel ID and length, projectile mass and an estimate of the friction. GASEQ puts the theoretical peak pressure for a 3x mix at 400 PSIG.

I suspect there is a problem with the Chrony reading. Perhaps the shock wave traveling through the metal gave a false second trigger? Spudfarm, what's the distance from the projectiles path to the top of the Chrony? The distance from the muzzle to the chrony?
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Unread postAuthor: SpudFarm » Mon Jul 07, 2008 1:24 pm

i am going to PM you the specs in metric jimmy..

the chrony was about 1m from the muzzle and i was firing pretty close to the chrony.
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Unread postAuthor: Pilgrimman » Mon Jul 07, 2008 1:32 pm

It may have been opaque gasses from the muzzle... I don't know much about chronographs, having never used one :lol:
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Unread postAuthor: Sticky_Tape » Mon Jul 07, 2008 1:57 pm

Well that's cool wish I could make a cannon like that.
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You can tell how awesome a cannon is by the pressure used.
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Unread postAuthor: SpudFarm » Mon Jul 07, 2008 2:20 pm

Sticky_Tape wrote:Well that's cool wish I could make a cannon like that.


you nailed it! i wish i was Larda. (yes i think i am going to start to work there sometime :D )

and i just found something stranger! i used one of those "pistols" with a wire and a camera at the end to look into the chamber and it is a whole lot of steel dust and dents in the rear end plate :S

i think i just got a DDT!
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Unread postAuthor: potatoflinger » Mon Jul 07, 2008 3:50 pm

Is it possible that you accidentally switched your chronograph to feet per second instead of meters per second? (not sure if that's even possible)
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Unread postAuthor: SpudFarm » Mon Jul 07, 2008 4:00 pm

i did many shots that where normal and i did not touch the chrony.
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Unread postAuthor: Sticky_Tape » Mon Jul 07, 2008 6:22 pm

you gonna fire it again if you had ddt?
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Unread postAuthor: SpudFarm » Mon Jul 07, 2008 6:28 pm

yes, i have used $1400 on it now and are not going to retrie it i am just not going higher than between 1x and 5x
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