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Supersonic?

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: ammosmoke » Sun Jun 03, 2007 5:31 pm

Well, as long as you can just set the torch there and get the hell away.
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Unread postAuthor: schmanman » Sun Jun 03, 2007 6:54 pm

spudthug wrote:schmanman we dont need u putting ur 2 cents in when we already established that i made a mistake....why are u always jumping to conclusions? read the other messages..



I read the other ones right after I posted that.

as you can see from my other posts this morning, I was pissed and I guess I was taking it out on people on this site. :oops:

I just doubted that you shot that fast.
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Unread postAuthor: noname » Sun Jun 03, 2007 6:58 pm

SpudBlaster, will the air expand from 200 psi to 350? I really doubt it, so I'll try from 300. Good idea though.
Ammosmoke, I prefer watching things get destroyed compared to hiding and waiting for them to be destroyed. :D
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Unread postAuthor: lukemc » Sun Jun 03, 2007 7:15 pm

first off spudblaster i was about to say that!! oh well great minds think alike (and so do ours :wink: )
any ways burst disks are amazing. my ghetto coke bottle burst disk (some where in the pneumatics section) even with a aluminun foil disk at about 20or 25 psi out performed my ball valve gun at 50. i would never beleive at 40psi (2 aluminum disks) i could shoot a marble clear though a milk jug. as for super or sub sonic its amost imposible to tell in your case unless you can dupicat4e it and shoot through a crony
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Unread postAuthor: SpudBlaster15 » Sun Jun 03, 2007 7:41 pm

noname wrote:SpudBlaster, will the air expand from 200 psi to 350? I really doubt it, so I'll try from 300. Good idea though.
Ammosmoke, I prefer watching things get destroyed compared to hiding and waiting for them to be destroyed. :D


Throwing CO2 cartridges into a campfire will cause their internal pressure to rise from 800psi to over 3000psi within the course of a couple minutes, so I think a starting pressure of 200psi would work fine.
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Unread postAuthor: jackssmirkingrevenge » Sun Jun 03, 2007 9:21 pm

SpudBlaster15 wrote:Throwing CO2 cartridges into a campfire will cause their internal pressure to rise from 800psi to over 3000psi within the course of a couple minutes, so I think a starting pressure of 200psi would work fine.


Do they go so high? What's the failure point of the opening one normally punctures?
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Unread postAuthor: spudthug » Sun Jun 03, 2007 9:25 pm

u know the disks on the top of the twelve grams? i recall that i read somewhere that that are 3k burst disks...so u may have a rocket if u throw one in there..
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Unread postAuthor: pyromaniac » Sun Jun 03, 2007 9:26 pm

Seeing my first post makes me look like an ass. now that ive read all that i feel stupid. :(
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Unread postAuthor: ammosmoke » Sun Jun 03, 2007 9:36 pm

noname wrote:Ammosmoke, I prefer watching things get destroyed compared to hiding and waiting for them to be destroyed.


Lol, I never said don't watch!!! I am not one to do that either. I just meant set it there with it on, and retreat to a safe distance. Not, run and hide, wait for boom.
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Unread postAuthor: SpudBlaster15 » Sun Jun 03, 2007 10:16 pm

jackssmirkingrevenge wrote:
SpudBlaster15 wrote:Throwing CO2 cartridges into a campfire will cause their internal pressure to rise from 800psi to over 3000psi within the course of a couple minutes, so I think a starting pressure of 200psi would work fine.


Do they go so high? What's the failure point of the opening one normally punctures?


Every cartridge I have ever thrown on a fire has ruptured, leaving the factory intended opening point in tact. It may be a result of surface area.
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Unread postAuthor: jackssmirkingrevenge » Sun Jun 03, 2007 10:25 pm

possibly, they're fairly thin walled containers, I was surprised with the ease one could saw one in half.
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Unread postAuthor: CpTn_lAw » Thu Jun 07, 2007 4:16 am

I'm not ok with the rapid conclusion of "if CO2 in fire rises pressure, then AIR heated up will increase pressure aswell." CO2 is a different gas than air. It behaves differently. Now, if you really want to increase your chambe pressure, add a few drop of water.
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Unread postAuthor: Hotwired » Thu Jun 07, 2007 6:55 am

*pump, pump, pump, pump, pump, pump, pump, pump*

*Sh*t! It's still not burst*

*What the smeg am going to do with it now?*

~ten minutes later after the disk finally gives way under the strain~

*KAB00M!*

*PING!*

*AHHH! MY EYE!*

I just had to :wink:

I like reliability and hoping for the burst disk to give up before your pump or some part of your cannon is something I'd never do.

Impressive damage results but unlikely to be supersonic.

Like jack said, you could have a massive chamber but it won't do jack (excuse the pun) to increase the projectile speed. Play about with GGDT and you'll find the speed increase with chamber volume gets increasingly small to the point where you're giving yourself another litre of extra chamber space to pump up for one more fps.

I know I could use a chamber a 10th of the size on my cannon and still only lose about 20fps on my usual ammo.

Nice work anyway ^_^
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Unread postAuthor: joannaardway » Thu Jun 07, 2007 7:15 am

I quote the ideal gas equation: pV = nRT

It states that the pressure of any gas (not a liquified one like CO2 though, because an equilibrium point is in plat there.) has a pressure proportional to it's absolute temperature.

Now, if you have a chamber of ANY gas at about 20 degrees C - or 293 kelvin, at 100 psi pressure.

If you then heat the chamber to about 313 degrees C - or 586 kelvin (twice the absolute temperature), your pressure will be 200 psi - twice as high.

Heating the chamber increases pressure - it works with anything.

However, your performance will raise much more than the mere increase in pressure would suggest. The faster gas particles and speed of sound increases velocity much further than expected.
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Unread postAuthor: noname » Thu Jun 07, 2007 5:37 pm

I'll probably put in some water and heat it, steam expansion will help the pressure a bunch. Thanks for the idea, Capt. Law.
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