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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

Quick Connects and Nozzles

Discussion about Compressors, hose, pipes, fittings, launchers, release mechanisms, and launch tubes.
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Re: Quick Connects and Nozzles

Post by tcarnahan » Thu May 05, 2011 9:25 pm

You know ... I had another idea. The concept of 3D desktop printing is just taking off ... see the article on it here ... (http://reprap.org/wiki/WebHome).

Even if I didn't have a machine like they describe yet, I could use freeware CAD software to design a plastic version of the metal QC. There are companies out there (see http://www.shapeways.com) who will take those designs and manufacture the part from your CAD design. The economies may not be there yet, but it should get cheaper over time. That may be the solution in my case.

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U.S. Water Rockets1
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Re: Quick Connects and Nozzles

Post by U.S. Water Rockets1 » Sat May 07, 2011 11:04 pm

tcarnahan wrote:
U.S. Water Rockets1 wrote:
The trick is finding fittings with the same threads as a bottle. The bottles are the problem in these cases. The threads are not standard with any common plumbing, so you have to modify gardena connectors to fit the bottle. There's a lot of ways you can adapt the threads by slobbering epoxy in them and letting it cure and form new threads.

I am aware of the problem of mating the QC to the rocket. I remember George Katz has a nice video describing how to address that problem. My problem is on the other end (i.e. Launcher to male plastic QC)

What type of launcher does U.S. Water Rockets use? I would imagine USWR has graduated into high pressure rockets. Do you use quick connects or some other method? (forgive me, I didn't have time to search the archives of this site to see if the answer is already there).

We have our own connector design that mates with our launchpad in a way that nobody else uses. It's a safe bet that a lot of people would give their left eye to know how that one works.

Since there are very few people (if any) launching rockets with very high pressure these days, there are a lot of suggestions based on pure speculation floating around which are patently false. From experience, we can tell you a few things, and debunk a few myths:

1) We started using plastic Quick Connects and Cable Ties, which both worked over 400PSI for us.
2) We had a lot of rockets explode on the pad back then, and the explosion would usually smash the quick connectors. We quit using them at those pressures and used cable ties from that point onward because they can take a blast without getting ruined.
3) We used cable ties without problems well over 1000PSI, but in our efforts to catch up to Anti-Gravity Research, we wanted to get rid of that flange on the back of the rocket (for reduced drag), so we created our own "twist lock" launcher. A properly made cable tie launcher will have no problem with larger pressures if you don't care about drag.
4) We refined that concept into our current design, which we have been using for many years, but only for the aerodynamic advantages.
5) Anti-Gravity Research used nozzles made out of ordinary plastic on their record launches as well.
6) We have never used a metal nozzle. All of our nozzles are made from plastic, or composite, or carbon. Metal parts attached to any pressurized part of the rocket should be considered a safety hazard and avoided at all costs.

The drawback of using plastic as opposed to metal is that it requires a lot more engineering effort to come up with a workable nonmetallic nozzle. Anybody can whip up a metal copy of a quick connect and screw it on a bottle and call it a clever design... but the second they enter it into one of the many international competitions, they get disqualified. Don't paint yourself into a corner if you don't need to. :)

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