Building a Better Rocket
Of course there is a lot more you can do to build a better rocket, and lots of resources online where you can see what others have done. Two areas where you can enhance your rockets performance are the engine and the nozzle:
It is possible to splice 2-liter bottles together to make larger engine modules. If done right, multiple sets of splices bottles can be connected together to make huge rockets. Here is a quick tutorial on how to do so:
Tutorial Coming Soon!
Add a Nozzle
Using the default mouth of the bottle as your nozzle is quick, easy, and very effective. However, you can drastically change the performance characteristics of your rocket by using a smaller nozzle to constrict the flow of your exhaust.
The most common way to restrict flow is by using a traditional Gardena style garden hose quick-release mechanism. However, there are a few issues with this that you need to keep in mind.
(pic of Gardena nozzle)
Attaching the quick-release to the bottle
The threads on a 2-liter bottle are similar to those of a garden hose adapter, but not the same. Depending on the length of the threads on the bottle, you may be able to simply add a second rubber washer to the quick-release and get a good seal with the bottle.
(pic of bottle, nozzle, and washer)
However, if the threaded area of the bottle is too short, you won't get a good seal. You'll need to adapt the quick-release by fusing it to a 2-liter bottle lid or use some kind of high-strength sealing tape to make it air tight.
Adding a Gardena-style nozzle means that most traditional launchers won't be compatible with your rocket. However, it's not hard to build a launcher specifically to work with this style rocket. You can see an example of one at the bottom of our launcher instruction page.
(pic of gardena launcher and rocket)
Launching a rocket with a restricted flow nozzle requires a very stable rocket. With a regular nozzle, the fuel (compressed air and water) is typically expended by the time the rocket is 10 feet in the air. So, even if the rocket does begin to tumble, there is no fuel left to push it off course and it continues to travel straight up.
However, with a restricted flow nozzle, the fuel lasts for much longer, so if the rocket begins to tumble early in its flight, the pressure of the exhaust will push it off course and it won't fly very high.
In our experience, a rocket with a Gardena-style nozzle doesn't accelerate as quickly, or fly as high, as an un-restricted rocket. However, our testing has been very limited, and our designs are still evolving rapidly. The real benefit of moving to a Gardena nozzle is the launch characteristics of the rocket.
A rocket with a normal nozzle will jump of the launch pad in a flash, reaching its top speed in the first five or ten feet of it's flight. Adding a Gardena nozzle makes the acceleration much slower. This makes the launch a lot funner to watch, as it causes the rocket to accelerate similar to much larger rockets.
In our discussion, it seems a good use for the Gardena nozzle would be combining a large rocket with a Gardena nozzle with smaller out-rigger support rockets using regular nozzles. This would give the large main stage a large boost from the support stages, while allowing the Gardena nozzle to continue to accelerate the rocket after the support stages have dropped off. We have yet to build a model like this, but can only imagine it would be awesome...