Water Bottle Rockets

When launching the rockets, I have the kids behind a rope 20 feet away, and they pull the launch cord from that distance. I'm right by the rocket pumping, but I wear safety goggles.

I talk about the importance of stability, which requires mass up front and fins in back, like an arrow. We want the rocket going up, not sideways and hitting someone.

The only rocket I've had burst was one I tried heating to reshape for better aerodynamics; that apparently made it brittle, and was the last rocket I heated.

Here's a quick overview. For a two-bottle rocket, cut an end off one rocket, and add weight to the uncut end of that bottle, either playdoh outside or kitty litter inside. For fins I use manila folders, which we can fold as needed. I make a middle fold, then two folds for tabs for taping the fins to the rocket body. I leave a gap so the fins and rocket body form a hollow triangle when viewed from above. The gap makes the fin more rigid, and the inside of the fin doubles the fin surface area, doubling the effectiveness of the fin.

For details, see How to Build a Water Bottle Rocket. You can see some pictures of the process and the result from a camp in Oct 2005.

I've been happy with a launcher I found on the 4-H site, http://ohioline.osu.edu/4-H/fguide00/4h_4.html. The launcher is from Versey Enterprises, 1258 North 1100 East, Shelly Idaho 83274, 208-357-3428, versey@juno.com. Price in 2005 is $50, inc shipping and handling. The original site http://www.ag.ohio-state.edu/~rockets/launcher_info.html, offers another launcher.

There are cheaper launchers, but be sure to get one that attaches firmly to the ground and has a launch tube, which is important for safety (to get the rocket going straight from the start) and performance (get good initial speed before losing any water).