A couple of months ago my son, Ashley, suggested we entertain my grandchildren on Xmas Day with a water rocket session.
Ashley was keen on trying a nozzle to screw on to the bottle that had the form of a garden hose fitting. There are plenty of YouTube videos showing successful rockets based on this design approach but all involve modifying a male garden hose fitting and gluing it to a bottle cap with a hole drilled through.
Granddad was contracted to do the design and manufacturing of the launch mechanism and screw on rocket nozzle. I decided that a one piece bottle cap with integral male hose fitting was the way forward. However this meant that I had to learn how to cut an internal bottle cap thread.
I used Solidworks to reverse engineer a bottle cap and male hose fitting and combine them together.
In this video, I show how made the nozzle including the cutting of an internal 8TPI (3.175mm Pitch) thread. I had to design and make a custom threading tool mounted in my CNC lathe. I used 8mm Silver Steel and hardened it by heating to cherry red, quenching in cold water, reheating to straw and allowing to cool naturally.
The plastic material is some mystery plastic rod I had in stock.
The launch mechanism is based on garden hose male and female fittings sealed with a conventional ½” O Ring. Releasing the grippers is performed by a bell crank and fork arrangement which depresses the outer jacket of the female hose fitting.
I had made water rockets years ago which performed very well. Ashley won a cash prize from Queensland University of Technology (QUT) with it.
The old design was very simple in that a rubber stopper with integral Schrader valve was used up the end of the bottle. The bottle was retained with 2 wire pins set across the bottle neck flange. Launch was simply a matter of sharply withdrawing the pins with mono-filament fishing line from a safe distance.
The new design proved very unstable in flight but very entertaining for the kids. I concluded that the instability was due to the added weight of the nozzle as part of the flight vehicle. I need to try to add compensating mass at the top of the rocket to move the centre of mass away from the nozzle end.
Post time: Jun-14-2017