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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: CpTn_lAw » Fri Jun 08, 2007 2:17 am

You're welcome my friend :D
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Unread postAuthor: sandman » Thu Jun 14, 2007 5:15 pm

oh to heat the water?

i thought you meant pump it up then add water to decrease the volume of the chamber since liquids cant be compressed
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Unread postAuthor: jimmy101 » Fri Jun 15, 2007 11:09 am

joannaardway do you ever feel like you are "tilting at windmills" on this forum?

Some people just have no concept of how a gas behaves... "CO2 behaves differently than air" or "add a bit of water to the chamber" are, or course, both wrong.

CO2 and air behave the same as long as you stay away from their critical points.

PV=nRT is the way to go. In the case of a CO2 cartridge heated in a fire the volume (V) and the number of moles of gas (n) and R are constants so it can be rewritten as;
P<sub>2</sub>/T<sub>2</sub> = P<sub>1</sub>/T<sub>1</sub>
or rearranged to;
P<sub>2</sub> = P<sub>1</sub>T<sub>2</sub>/T<sub>1</sub>
This form of the ideal gas law is usually called "Gay-Lussac's law".

Adding water to the chamber will not increase the pressure very much. It will increase the energy in the chamber by a very large amount but you won't be able to capture that extra energy unless the pressure and temperature of the gases drops below the condensation point of water vapor before the projectile leaves the barrel. That is a very hard thing to do in a gun.
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Re: Supersonic?

Unread postAuthor: TwitchTheAussie » Tue Jun 19, 2007 7:04 am

noname wrote:I can barely hear now.
Give me your opinion, was it supersonic or not.


Sorry bout this but I was too lazy to go through all the pages but did you hear a crack with the shot? If you did that was your projectile hitting and smashing the sound barrier to pieces.
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Unread postAuthor: rna_duelers » Wed Jun 20, 2007 12:52 am

Just because the presence of a loud report doesn't mean the sound barrier was broken by the projectile.Unless the air was heated I very much doubt the sound barrier was broken by the projectile.In the range of 900fps sounds more realistic.Having normal air used in any cannon with any valve is near impossible to break the sound barrier.

There are plenty of reports you can read on this site to verify reasons why the sound barreir cannot be broken with normal compressed air.
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 20, 2007 2:55 am

rna_duelers wrote:There are plenty of reports you can read on this site to verify reasons why the sound barreir cannot be broken with normal compressed air.


The loud report probably is a sonic crack, but is a result of the air breaking the sound barrier as it exits the muzzle, not the projectile itself.

It is possible to break the sound barrier using compressed air, there are commercially available pneumatic rifles such as the AirForce Condor that are capable of doing so.
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Unread postAuthor: pyrogeek » Wed Jun 20, 2007 3:30 am

spudthug wrote:@noname: what is the best burst disk u have used at a 4x mix? also waht mix are milk bottles good for?

also does anyone know how to wire up a stun gun to 2 spark plugs?? i will be posting a thread asking this question soon reply there..


Just wire them in series. One lead from one terminal of the stungun to the top of one plug, and then a wire from the base of that plug to the top of another, and a wire from the base of the second one to the other terminal of the stun gun.
Although, if you are using it for a hybrid, don't bother. The gap must be smaller and smaller as you use it for higher and higher mixes. You can try it though.
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Unread postAuthor: frankrede » Wed Jun 20, 2007 4:49 pm

noname wrote:By sticking on a peak pressure guage, I figured (when it worked as a hybrid) 1x would get me about 90 psi, 1.5x would give about 140 psi, 2x would get me about 170, 2.5x got around 215, 3x about 250, 4x about 310, and I didn't test past that.
I wouldn't recommend using soda can burst discs for PVC guns, because one layer takes around 170 psi to burst.
PVC Arsenal, I got hit by one of the bearings once. At a 2.25x mix, the ball bearing got shot through 4 soda cans and hit a piece of steel pipe that was lying around. It gave the pipe a 1/4" deep dent, bounced back, and tapped me on the kneecap.
I have tryed using soda cans in my hybrid and they burst at less than 90 psi.
either they burst or slipped/
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Unread postAuthor: SpudBlaster15 » Wed Jun 20, 2007 6:29 pm

The burst pressure of the disk depends upon surface area. Chances are, you are using a much larger union than noname.
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Unread postAuthor: noname » Wed Jun 20, 2007 7:41 pm

Yeah, frank, you're using a 2" union and I'm using a 1/2" one. I was also double layering the soda cans, which increases strength more than half.
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Unread postAuthor: hoastmaster » Thu Jun 21, 2007 10:28 pm

rmich732 wrote:I elaborated on the gangsta theme....

anyways...

PVC Arsenal, I doubt that there IS a valve faster than a burst disk. Full flow, rapid opening... can't beat it.

The only valve better than a burst disk valve... is a BIGGER burst disk valve.


i disagree
there is such a system the military used in sa
an iris shutter on a charged opening mechanism is alot faster then burst disc
my dad tells me they used air tanks used in jets for life support as the chamber (around 1000bars of pressure) attached to the iris shutter smacked onto a 24ft 1/2" thick iron pipe 1, 1/2" dime
and used a iron ball bearing as the projectile
lets just say it was loud and it was nasty the set the hole cannon mountings made of concrete

the result was around 3500fps no kidding
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Unread postAuthor: noname » Thu Jun 21, 2007 10:40 pm

Let me know when you get one of those for $2.50 and set it to beat a burst disc, then I'll think about one. :wink:
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Unread postAuthor: hoastmaster » Thu Jun 21, 2007 11:01 pm

price wise yes burst disc are un matched but i was merely stating the insane things that can be achieved
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 21, 2007 11:14 pm

i disagree
there is such a system the military used in sa
an iris shutter on a charged opening mechanism is alot faster then burst disc


You can't get faster than a burst disc, it gives maximum flow instantaneously.
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Unread postAuthor: hoastmaster » Thu Jun 21, 2007 11:27 pm

an iris system on powder opening charge is the fastest release valve on the planet

ill post again with some pics of the system
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