This rocket contains metal components, so it violates the universal "no metal rule” for water rockets. However, it does work so well, the rockets fly great, so it’s worth mentioning & documenting. This is a long page and expains the whole process in exhaustive detail. Even if you do not intend to build a Lamp Rod Rocket, there are some interesting construction technics described.
These four water rockets (eight each 2 liter bottles total) have been joined together by simply screwing double sided bottle caps together. Each water rocket is actually two each 2 liter bottles joined together with a short threaded lamp rod, so BOTH bottles in each rocket assembly HOLD PRESSURE.
In April 1997, I attended daughter Heather's (pictured at left) Discovery Middle School carnival. I brought 11 different styles of rockets, and had 75 great launches within a 2 hour period.
ONE ROCKET (with only two each 2 liter bottles) PERFORMED EXCEPTIONALLY, and here's the detailed story how I constructed it.
A special praise to Bill Robinson of California (USA) for submitting the original idea of using threaded lamp rod. We now dubb this the "Robinson Coupling". I've experimented and improved to make the process stronger and air tight. The final result is a rocket that blows the socks off all the other rockets I've made.
Basically, this rocket performs better because it holds larger volume of air, and half of the air is DELAYED because of the reducer, which is the threaded lamp rod. This rocket is also noiser, making a swishing sound. Once it gets it's initial blast off and speed, the delayed air pressure (from the second chamber) carries the rocket further.
Navigation is on the right for various Lamp Rod Rockets construction pages.