Some friends & I used to use the model rocket engines to make huge "bottle rockets." We'd take the plug out of the top end of the rocket engine & fill the top with powder we took out of firecrackers. Then we'd plug the top with a sodium silicate (IIRC) solution that hardened almost like rock. After that we glued the engine to a 1/4" dowel rod. You had to make the rod just the right length to make it balance right so it'd fly correctly. Stick it in a piece of tubing stuck into the ground, poke a fuse up inside the bottom, & follow the standard fireworks instructions. "LIGHT FUSE, GET AWAY" You can imagine how high up they went before the BOOM.
(Don't tell any of my kids about this. My wife's a doctor & doesn't want them handling fireworks at all.)
