New Gardena launcher

Water Rockets NSW

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Ian Christie
Rocket Onlooker
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Joined: Thu Dec 04, 2008 11:42 am
Location: Melbourne

New Gardena launcher

Postby Ian Christie » Fri Dec 18, 2009 12:20 pm

At VSSEC (Victorian Space Science Education Centre) we have recently built and tested a Gardena style launcher which uses the larger 3/4 inch / 19mm "tail" (nozzle). For a total cost at Bunnings of just under $23 plus a bicycle brake lever and cable we built a launcher which has four times the nozzle cross sectional area of the standard "tail" (nozzle).
We found a simple method to attach a 3/4 inch plastic pipe connector instead of a hose to the quick release which means that the whole thing can be made by just threading plastic pipes together. No special tools or skills required.
We have been fitting the nozzle to a bottle cap by gluing it in with a hot glue gun. Part of the trick here is to put a bead of glue inside the nozzle. another around the edge of the cap, press in the cap and then heat the nozzle and cap in boiling water so that the glue softens and the cap can be manipulated to get it secure, straight and sealed.
We have tested this system to 150psi without leaks or other failures.
One of the things we have noticed is that the large nozzle size allows for such a high exhaust velocity when the rockets are charged with just air (no water) that the performance is much better than with the smaller nozzle and no water.
We are in the process of writing a set of instructions for building these launchers but since we close today until the end of January it won't be done until next year. In the meantime if anyone is desperate to know how this is done email me at ianchristie@optusnet.com.au and I will send you an incomplete draft and photos of the prototype.
Cheers
Ian

air.command
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Location: Sydney, Australia
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Postby air.command » Fri Dec 18, 2009 8:50 pm

Hi Ian,

Sounds like your new launcher is working well. The larger Gardena nozzles (15mm ID) are definitely a nice compromise between the smaller 9mm Gardena nozzles and the fully open throat of a bottle (22mm).

That is also an interesting procedure you have there with the hot glue for attaching the bottle cap. With these nozzles we normally just use epoxy to hold the bottle cap in the plastic quick connector. I've always had problems getting hot glue to stick to the polypropylene caps but if you are getting 150psi with them then that's great. :)

The larger nozzle size also allows you to use a decent size launch tube to get even more altitude from your rocket.

I look forward to seeing the instructions when you have a chance to put them up.

cheers

- George


PS. Here is a rocket (Polaron VII) we flew with one of these 15mm nozzles this weekend using a 1.2m long launch tube: http://www.youtube.com/watch?v=8A_UhNFOqZ8
Crop Circles: ... just a bunch of guys looking for their rockets ....


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