Turn Plastic Bottles into Rockets

Mythbusters had a segment on this game show in Japan that showed a person getting carried 30 feet by a rocket pack made of soda bottles. While they didn't get a person to lift off they did get some really great height, the record is 517m.

There used to be a plastic toy rocket you filled with water and pumped up. Worked the same way, except not so pricey and everything was ready to go, not some kit you had to put together.

My boy's Cub Scout Den made their own with soda bottles, rubber stoppers, tape and scrap cardboard. Why pay over $15 a pop (pun intended) for the kit?

Building compressed air/water propelled bottle rockets is a thriving hobby. There are lots of sites out there on the net, and people have gone to extreme lengths for performance (e.g., carbon fiber reinforcing the bottles to get greater pressure). There are even 2-stage rockets. Lots of free plans are available, and the parts are generally easy to find. Here's a good place to start. Some of the more complex and exotic design techniques can be found here

Both of these sites even include links to simulation programs and Excel based modeling spreadsheets. These folks are SERIOUS!