Water Rockets

Here is something I found surfing the web awhile back that turns out to be a lot of fun: Water Rockets! Simple construction for both launcher and rocket, benign fuels, cheap to operate, unexpected performance. Just a little imagination and some common sense can make for a safe, interesting hobby.

The basis of this subject is the plastic soda bottle. Refuse, except for possibly the token refund it might be worth, it is light and able to consistently hold pressures of over 100 psi. All of my time so far has been spent with the 2 liter size, but the range of sizes that I know of are from 3 liters down to 20 oz. A nice thing about the 2 liter size and below are that the inside diameter of the opening is ~0.850 inches. The reason that this is nice is that the outside diameter of 1/2 inch pvc pipe is 0.840 inches. A nice sliding fit! This relation is the basis of a family of launcher designs, including the one I use.

Launching the rocket is a simple matter and very impressive to someone who has not seen it before. The rocket is half filled with water and, while holding it upside down, the launcher is place on the rocket. A little twisting is usually necessary to get past the o-ring. Then everything is turned right side up and placed on the ground with the string to the trigger routed underneath the launcher, so when the string is pulled the trigger will be forced toward the ground. Lifting the trigger up into place forces the ends of the cable ties over the flange at the nozzle of the rocket, locking the rocket in place. Using a bicycle pump, with some kind of pressure gage, connected to the Schrader valve on the launcher, the air inside the rocket is compressed to 80-90 psi. A tug on the string lowers the trigger allowing the cable tie ends to fall away from the bottle flange. With a "PHOOMP" the rocket disappears from the launch pad. Your eyes race to keep up with the climbing rocket, amazed that you can get that kind of performance from a garden hose and a bicycle pump.