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Speed of Sound

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Speed of Sound

Unread postAuthor: ShowNoMercy » Fri May 18, 2007 7:45 am

I have a spuah valve, and I was planning on making a large cannon this summer, so I decided to make it a goal to hit the 340 m/s mark. I was wondering if anyone had any suggestions on whether a large heavy projectile is better than a smaller one? And also how to make it so I do not have a large barrel, I put in some prelim numers into GGDT and it was telling me I needed like a 20 foot barrel. So any help would be greatly appreciated.
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Unread postAuthor: jackssmirkingrevenge » Fri May 18, 2007 7:54 am

A small light projectile saboted in a large diameter barrel would work best - take a hint from modern anti-tank ammunition. Also, if you can find a regulated helium source all the better.
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Unread postAuthor: ShowNoMercy » Fri May 18, 2007 7:56 am

Thats what I was thinking, I was trying to use a 10 gram projectiile and then use a larger sabot to allow more force to act on it but I am still getting some huge numbers that I need to make.
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Unread postAuthor: dongfang » Fri May 18, 2007 10:53 am

Hi,

Yes, small density is definitely easier.

I got Mach 1.13 from a pure combustion, with a very light projectile from a very long barrel..

Regards
Soren
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Unread postAuthor: spudthug » Fri May 18, 2007 2:06 pm

dongfang.. i highly highly highly doubt that u got over the speed of sound witha combustion...actually i dont doubt it, it isnt possible.. it is hardly possible for a big pneumatic...unless u have helium or hydrogen...witch hydrogen is better but no one is stupid enoguh to use that...
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Unread postAuthor: Pete Zaria » Fri May 18, 2007 2:11 pm

spudthug wrote:dongfang.. i highly highly highly doubt that u got over the speed of sound witha combustion...actually i dont doubt it, it isnt possible.. it is hardly possible for a big pneumatic...unless u have helium or hydrogen...witch hydrogen is better but no one is stupid enoguh to use that...


Wrong. Someone already launched a pingpong ball over mach 1 and chronographed it to prove it, using a butane-burning, atmospheric-pressure combustion gun. It can be done, it just requires a nice c:b ratio, a longass barrel, the right fuel/air mixture, and a very light projectile (like a pingpong ball).

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Pete Zaria.
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Unread postAuthor: )DEMON( » Fri May 18, 2007 2:15 pm

spudthug wrote:dongfang.. i highly highly highly doubt that u got over the speed of sound witha combustion...actually i dont doubt it, it isnt possible.. it is hardly possible for a big pneumatic...unless u have helium or hydrogen...witch hydrogen is better but no one is stupid enoguh to use that...


You are really the general idiot of these forums, no offense but stop posting out your asshole. You know you can't just live in your own world where your own made up laws of physics apply to everything. I have seen someone go super sonic with a combustion, it had something like a 5m long barrel. Don't you have anything better to do than ruin someones day?
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Unread postAuthor: boilingleadbath » Fri May 18, 2007 4:54 pm

Calm down, or I'll calm you down myself.

1) Combustion gasses are hot, which means that they have a higher speed of sound than the gasses in a pneumatic's air, which makes it easier to exceed 340 m/s

Pneumatics, admittedly, have an advantage the "<i>practical</i>" regime - say, sub 800-900 fps (that's a wild arsed guess)... but that's only because of the higher pressures.

(As a note: the gasses get cooler as time and barrel length go by, so it's probably best to use a higher C:B ratio than normal)

2) Of course a ping-pong ball isn't a practical projectile... but so what?
The entire endeavor (surpassing that magical velocity) isn't practical; we'd probably be best off in any regard (distance, muzzle energy, damage) if we keep speed at around 500 fps and used heavier ammo.

...so the fact that the projectile is only supersonic for 10' isn't relevant.

3) People have documented supersonic speeds with a combustion launcher... indeed, speeds well into the supersonic regime.
Don't tell them that they didn't.

4) I'm not so sure that a large diameter barrel is what you want:
* Valve restrictions hinder them
* Combustion times hinder them
* They imply heavier projectiles
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Unread postAuthor: paaiyan » Fri May 18, 2007 4:57 pm

Yes, small barrel better. OH OH OH! You could shoot frozen peas. Finally, a good use for that crap.
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Unread postAuthor: Velocity » Fri May 18, 2007 5:53 pm

If I was going to build a supersonic potato cannon...

1) I'd go small diameter. It is easier to get a smaller projectile to break the sound barrier than it is to break the sound barrier with a larger projectile.

2) Use some type of burst disk. Their instantaneous opening time and full flow are ideal for maximum performance.

3) Use metal as a building material. It can take more pressure, and it looks cooler too.

4) Consider the option of a hybrid. They generally get much higher velocities than pneumatic or combustion spudguns combined.

5) Work closely with GGDT. Their are many little variables that you can plug in and test with GGDT in order to get the best possible performance.
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Unread postAuthor: TwitchTheAussie » Fri May 18, 2007 5:56 pm

Yeah go a full metal hybrid so much more power and you can try the new piston hybrid created by...oh crap forgot but anyway. Just go hybrid and metal and make it a pea shotgun :lol:
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