This launcher uses one metre of PVC pressure pipe. It is a very close fit within a PET bottle neck, so close that rapid placement of a bottle over the launcher causes the bottle to bounce up and down due to the pressurised air being unable to escape quickly. With some bottles there is some friction with the pipe, though this does not appear to be a problem. This size pipe is readily available in Australia, New Zealand and the Cook Islands, possibly elsewhere.
As pictured the launcher is set up for a vertical launch. The launching angle may be adjusted by untying the light rope and adjusting the length, as pictured passing horizontally between the two hinged pieces of wood.
A broom handle provides stability at an angle perpendicular to the two wooden legs, the broom handle is placed so equal lengths protrude from the pipe through which it is placed. One wooden leg is held down with a tent peg, this is essential, particularly for vertical launches as otherwise the launcher may be pulled over when pulling the release string.
I have now made what appears to be a reliable release mechanism, see below:
This release mechanism held a pressurised bottle in place when I accidentally pulled the launcher over, causing it to hit the ground pointing almost directly towards me. This is not something I recommend trying.
A simpler friction release mechanism also may be used, but the exact release timing cannot be controlled.
Click here for details of the first half-way respectable rocket I made (24K).
Click here for a summary of my own learning about water rockets and the physics involved.
