Pneumatic / Combustion Performance Disconnect


Postby LukeSkyRocket » Mon Jan 01, 2007 12:32 pm

Sorry to kick an old topic, I hope I don't offend anyone.

the discussion of flameholders and jet ignition reminds me of the tennis ball mortar. These things are traditionally made from 3 pringles cans taped end-to-end. The bottoms of the top two cans have large holes cut through them (leaving a washer-shaped peice of thin metal protruding into the inside volume of the gun.) Since the tennis ball can't pass through either of these, the barrel is simply the top can. That leaves a chamber with twice the volume of the barrel. Should be very inefficient. But the interesting thing is that the bottoms of the cans with the holes in them create baffles. So maybe this has something to do with why the tennis ball mortars actually shoot (but I don't know if they work well or not.)

It might be interesting to try putting similar baffles in the chamber of a simple combustion to see what happens.

Also, someone needs to put to rest permanently the conflict about what pressure a burst disk should break at (one side saying it should be low, allowing the combustion to continue as the projectile travels, and avoiding the loss of heat to the chamber walls; the other side saying that developing higher pressures should create more acceleration.) We need a way to test this.
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Postby benstern » Mon Jan 01, 2007 1:00 pm

The most universal way to test most performance enhancing innovations on spudguns is the use of a chronograph in a controlled setting.

This usually means shooting indoors with the barrel pointed out a window or door. Objects might be used to catch or stop the uniformly shaped projectile.

So, who is gonna test this?
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