My brother in-law Kirk built a great water rocket launcher and a handful of rockets (using his trademark Mountain Dew bottles) when he was visiting last year. With the nice weather it was time to get them out again. We took a break at work on Friday, grilled hot dogs, and shot water rockets. Great fun.

We haven't quite worked out what features make for good flights. So far it seems that some fins with a little weight in the tip results in a rocket that establishes a good spin, maintains direction, and attains impressive height. The problem is that the extra weight causes it to smash into the ground with a lot of force, eventually pealing off parts of the rocket.

Today I came up with a new design. It uses a two liter bottle for extended altitude, a one liter bottle on top to help with aerodynamics, and a detachable nose cone which provides weight as well as a parachute enclosure. I figured that it would reach apogee at a hundred feet or so, begin to tumble, the weighted nose would fall off, parachute cleverly deploy, followed by a nice gentle glide to earth.

Instead it took off in a glorious rush of water, reached forty or fifty feet altitude, and the parachute deployed early. A microsecond of abrupt air brakes, the parachute material forcibly ripped from the strings, and the rocket tumbled back to earth.

Back to the drawing board...

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