You can find water rockets all over the web. Here are some pictures and movies of our first experiments. To pump up the bottles, a gas cylinder was used. We used it to go to pressures up to 8 Bar.
The first picture shows the launching nozzle and release system. The bottle is fixed by a U-shaped piece of wood. In this way the moment of launching is not determined by the tightness of a cork but can be decided manually.
The side views show the gas tube and the complete launching platform. A launching tube is removed for these pictures. Lauching bottles from a tube gave better results because then the bottles are stabilised at the moment their speed is still low.
First lousy shot
Filmed from the attic
Launching method (884KB)
To calculate the height of the best shots, the launching speed was estimated from filmed material. Within one frame (1/25 sec.) the bottle achieved a height of about 1.5 meter. This is 37.5 m/s. Since
with m the mass of the bottle, v the speed, g the gravitational constant and h the height. We can find
which is a very rough estimation. By observing some shots from the attic I think the achieved height is slightly lower.