Spudgun! And what a spudgun...

[buffo]

I just remembered another fun pastime... Dry ice bombs. These things are really great. Put an inch of water in an empty plastic soda bottle, drop a few pieces of dry ice in the bottle, and quickly screw the cap on and toss the bottle. When the dry ice sublimates to a gas it will build up pressure inside the bottle until it explodes with a thunderous bang!

Note: This will work with any size bottle, from a small 16 oz one all the way up to a 3 liter one. You just need to add more dry ice for the larger bottles.

Be careful the damn thing doesn't go off in your hand though. After a few experiements you'll get a feel for how much water and dry ice to use. But don't go near the bottle once you've capped it. I one had one sit for over a DAY before it exploded. On the other hand, if you put too much dry ice in, the thing may explode as soon as it hits the ground. (I even had one go off in mid-air once.)

For some real fun, tie a string around the bottle, tie the other end to a brick, and drop the whole mess in a swimming pool. (Or even a 5 gal bucket of water.) The resulting splash will be impressive.

Adam

[aaron_inc]

hmm, i never thought it was possible, i used to be a member of all the spudgun froums and they all said that air will not move that fast, unless it was superheated but if you have seen it happen then it must be true.

[buffo]

Hey Arron Inc;

I poked around a few of those spud gun forums years ago, and yeah, you have to watch out what some people post. Like the guy that swore that using PR-200 PVC pipe (which is a step below schedule 40 and is thin as hell) was safe to use on his acetylene-oxygen-mixture-powered potato gun.!.

His theory was that if the pipe failed, at least it would fail at a lower pressure and thus the resulting concussion would be less dangerous than if you used something stiffer - like schedule 80 PC or even carbon steel pipe. Of course, he totally missed the concept that using acetylene as a fuel was dangerous and stupid no matter what material you used for the gun, and that any explosion - even from the failure of PR-200 pipe - was likely to cause serious injury. Wonder what ever happend to him... (Maybe there's a video of him on YouTube losing an arm!)

But common sense tells you that if you need more force than you can get from hairspray (or Static Guard), then it's time to switch to compressed air. It may be a bit more expensive to build, but that's better than risking an explosion. Unfortunately, some of the info on those spud gun forums was sorely lacking - at least when it came to safety.

I wish the BFPG-9000 website was still up, because not only did the guy have some very cool pictures of the thing, but he also had detailed calculations showing how, before he ever fired it, he was reasonably confident that it would be able to exceed mach 1. I seem to recall that he used some pretty expensive mathmatics software (I think it was MLab, but I'm not certain) to model the fluid dynamics of his dump valve and barrel assembly, and yet he presented the whole thing with a clean layout that was easy to follow - even if you weren't a physics buff. (I remember that he was a college student, and used the university's software to do the modeling.) I hadn't been through those forumulas since I was in the Navy (Nuclear Power School, to be exact), which was a long time ago, and I could still follow them pretty well.

The great part was that his calculations were quite accurate. When they actually tested the muzzle velocity, he was within a few percent of the speed he calculated. Evidently his instructor was pleased...

Unfortunately, the page was taken down when the kid graduated from the University of Kansas, and I haven't seen a mirror of it since. (Though I did find this picture series from one of his early tests of the beast. Check out what's left of the watermelon!)

Adam

[aaron_inc]

wow that thing is pretty big, what kind of valve has he got on it? i remember that there used to be a calculator on the internet somwhere where you put in the gas your using, the pressure, the size and shape of chamber, width and length of barrell, type of valve, time for valve to open etc. if you do some searching on spudfiles you shoud find it.