SpudFiles

Upon the absolute failure of the last 'supersonic spud' thread, I have decided to revive a forsaken topic and present a fourfold question.

1) Is it aerodynamically feasable to fire a golf ball from a direct injection propane combustion 'spud' gun (metalloid barrel and chamber, of course... this is out of PVC league) at speeds in excess of 2800 ft/s (720m/h, ~320m/s, mach 1)?

2) If it is feasable, what would be the optimal barrel length, chamber volume, chamber:barrel ratio, and build material for said supersonic speeds; does the phrase 'bigger is better' apply here, or does efficiency drop off after a certain size?

3) Have there been any previous attempts/successes at supersonic speeds in the history of direct injection propane, (no hybrids, oxy-acetyline mess... straight propane.) and, if there have been, could you provide a link?

4) Given the previous three are true, Is it possible to reach mach 2 by any means, hybrid, and what not?

Eventually, we just start looking at a slug fired out of a shotgun of sorts; except without black powder. And much more illegal. 8)


If we can actually create and compile a comprehensive thread with all the data in it, we might be able to build a few DIY supersonic 'spud' guns. Which would be awesome.

Golf balls would make ideal projectiles for this, but i'm sure racketballs would work... tennis balls have too much fuzz and would probably warp to an odd un-aerodynamic shape. Hence, coefficient of drag would be too high at peak for supersonic speeds to be substantiated long enough to be significant.


Oh. And, I've used tfse. However, to no avail. I research before I post, unlike some people...

Cheers.
Mike.

We've barely touched the barrier, some hybrids have broken it, helium powered pneumatics have done it

Why is everyone these days trying to make a "supersonic" combustion?

On that subject, I plan on making a supersonic pneumatic in the future although I was wondering, for those who have achieved this with a pneumatic, how loud would you rate the noise levels in comparison to a 12 gauge? Or any sort of firearm really..

I think RNA_DUELERS is making a supersonic pneumatic at the moment. He said something about 300 psi helium???

Man why use helium? A hpa tank with a stabilizer does the trick...

Mach 2?
I figure mach 6.6 is about the fastest you can get with a propane-air combustion. (based purely on the temperature of the flame)

I figure that, if you used a large number of ignition points (to get it up to pressure quickly) and a large C:B ratio (so the gas doesn't expand too much and cool off), mach 2 shouldn't be an issue with light projectiles.

However, EVBEC is suggesting that getting a golfball to M2 would require more than 5,000 cubic inches of chamber volume - that's basicaly a 8" pipe 8' long.
Nevermind the barrel, which would be 100' of sdr 21 - although a sabot could be used.

A hybrid would help. I'm not sure how much, but probably by a bit more than the mix used. (3x mix = 3 times smaller)

Jolly Roger wrote:Man why use helium? A hpa tank with a stabilizer does the trick...

hpa tank ? What's that ?

Google?

ok, found it

If this is a standard combustion then making the chamber out of metal wont help you any.