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air pressure versus muzzle speed linear or NON linear?

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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air pressure versus muzzle speed linear or NON linear?

Unread postAuthor: rgormley » Sat Oct 07, 2006 12:15 am

Any body know if the increase in pressure versus muzzle speed is NON linear??


One if the engineers who play around with hydraulics said that there is a very non linear curve of air compression pressure versus muzzle speed

Presume to do with how air compresses

Any ideas?
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Unread postAuthor: rna_duelers » Sat Oct 07, 2006 5:36 am

Wait for BLB,he's pritty much the smartest on here.He should be able to answer that.
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Unread postAuthor: boilingleadbath » Sat Oct 07, 2006 6:05 pm

Assuming a weightless gas (lol), the corresponding compleate lack of flow restriction (good luck keeping it in your chamber), and an infinite chamber volume... you'll find that muzzle velocity goes as the square root of the pressure (in PSIG).

Muzzle energy, in this hypothetical situation, WOULD go liniarly with pressure.
This is a good aproximation for shooting heavy projectiles - any valve worthy of the title won't restrict flow noticably and gas dynamics arn't terribly important at low speeds.

However, adding weight to the gas makes it harder to reach high speeds. This flattens the curve somewhat, especialy at high pressures.
Limmiting chamber volume probably makes the curve even more curved, though - especialy at low pressures.

But... anyways, it's not liniar. Go plug some numbers into the GGDT if you want to know a closer approximation for your specific launcher.
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Unread postAuthor: drac » Sat Oct 07, 2006 8:52 pm

Kinda funny, this topic comes up after a little post about my PreCalc project. ;)

That is what i was wondering, because if it isn't linear then it shoots my whole project to hell.
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Unread postAuthor: joannaardway » Tue Oct 10, 2006 1:20 pm

The relationship is definately not linear between pressure and MV. (It does relate to the square root of pressure, given a fixed launcher, and a decent valve)

However, the relationship between GGDT results and actual results should be a linear-ish realtionship.

Or so I would believe.
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