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I was wondering if anyone could help me with building a super sonic potato gun. I would really like to know if there is any mathimatical equation to take the volume and pressure of the pressure vesel and use that to find out how long the barrel will have to be for a certain speed.

It takes a good knowledge of thermal dynamics and physics to figure that out. Your best bet would be to use the Gas Gun Design Tool, downloadable in the Tools/Calculators Section.

Speed of sound at sea level is 714 MPH, or 340.29 m / s. Use the GGDT or similar as Drac suggested to calculate what you'd need to get there. You'll either need a huge pnumatic with a golfball barrel or a hybrid. Don't mess with hybrids unless you REALLY know what you're doing.

Peace,
Pete Zaria.

why a golf ball barrel?

but yes i think you would need a hybrid...a big one....and i wouldnt go there unless you really know what your doing

It's impossible to make a pneumatic go obove the speed of sound with usual air,you need to use a different type of gas heluim or Co2 to reach the speed of sound and it can be done with a small piston gun and a marble quite easily.

For what reason can you not use regular air to reach the speed of sound, and what is the Gas Gun Design tool.

Google: "Gas Gun Design Tool"

The reason is too hard to explain to bother wasting my time telling someone who can't even be arsed to UTFSE!

boilingleadbath wrote:Google: "Gas Gun Design Tool"

The reason is too hard to explain to bother wasting my time telling someone who can't even be arsed to UTFSE!

utfse = use the fucking search engine?

anyways, i'd kinda like to know, myself..
something to do with valve opening time, and that since air can only go so fast(maybe ONLY the speed of sound) the valve slows it too much to actually break the sound barrier.
just a guess though, please enlighten us?

Yes, zvallance, UTFSE = use the fucking search engine

And you basicaly got it; air is limmeted to the speed of sound, and (even with a perfect valve) the amount of force it could apply to the projectile trails off as it gets closer and closer to that speed - and thus you never quite reach it.

Note that because the speed of sound increases with gas temperature, and the propellent gas is heated by shocks and friction in the barrel, 'supersonic' - compared to the outside air, not that in the barrel - projectiles acctualy are possible with normal air.
It's just that the very slight degree by which they are supersonic isn't worth the extra hassle.

Incidentaly, the only gasses that can push a projectile past the speed of sound in air are hydrogen, helium, and possibly nitrogen.
CO₂ acctualy is limmeted to providing mach .85

Ohh well you learn something everyday CO2 is limmited below the sound barrier.

Iam building a Hybrid, when I get it up and working Ill let you know if i hit supersonic. What does that sound like? A sonic booom?



Josh

Any sonic boom would be covered up by the explosion in the combustion chamber. An example is a .22 bullet-it goes past the speed of sound, but no sonic boom.

Try to post things that would help people in the present time not a few months back.

Im sorry but does anybody here have any pictures or better yet videos of supersonic cannons, any links. Because i have searched this manytimes but its like a myth, there are articles but no pics or storys.

joels cannon on spudtech. its pretty simple too. i guess supah valve + long barrel = supersonic pneumatic cannon! i dont know if there is really proof of it but i dont think joel would lie on something like that.