Back in 2000 and 2001 my brother and a buddy of mine built one with all the money we could gather. It was pure luck that we didn't blow ourselves up with the thing. It was about 15 ft long and the biggest chamber diameter was about 8 in. Pure flammable propellant and a grill lighter!!!! (Got the gas chamber to glow orange more than once, and even blew the threads off one of
these.) You should have seen the look on the check out clerks face when she saw 3; 16 year olds buy 4 bottles of diesel engine starter (love the ether).
We did quite a few trials with it and it worked great...heck we actually shook the windows on his back porch once. I wish I had a picture of this beast, but since then my friend has moved to TN and he is now attending Georgia Tech. Infact, I believe it's still in his grandparents garage.
I know the technokats have an air powered canon this year. I've seen it in use a few times and it's pretty cool. You might keep an eye out for them in Atlanta because I know they had it out in Chicago.
