FLONE's question redux

Just starting to spud and wonder how long your barrel should be? Want to know how to build a better cannon? This is just the place! If you think your question is one of a newcomer, please post it in here. If your question is posted elsewhere, and it's a newcomer's type question, it will be moved in here.

Postby SpudBlaster15 » Fri Dec 08, 2006 10:59 am

A good demonstration of jimmy's statement is Latke's C:B ratio tests using a 1.5" barrel and a .22:1 C:B ratio. Latke experienced a contraction effect as the spud tried to exit the barrel, caused by the cooling gases returning to their original density.
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Postby boilingleadbath » Fri Dec 08, 2006 6:54 pm

...I'm looking at the turbulence in the <i>fuel/air</i> mixture - and it hasn't burnt (or it wouldn't be a fuel-air mixture, would it?) yet, and thus hasn't been heated very much... so, indeed, it's density at 1 atm will be about 1.5g/l, and so it'll be compressed to about 4.5g/l at the moment in time I'm considering.

Now, a couple ms later? You'd be much closer to the truth, although not perfectly, because the pressure would take time to be trasmitted back to the chamber.

OMG! <i>That</i> is why your pressure increase from this effect isn't as great as "mine"; "my" "pressure probe" is attached to the projectile, and yours is in the chamber. It takes a few ms for the gasses to switch directions and move back into the chamber and reverse your pressure curve - during which time the projectile is being propelled along, "consuming" some of those prepellent gasses in the barrel (which makes your bump smaller than mine)
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