This rocket slips onto a 1" PVC pipe, to be fired by compressed air.

Our best launch was 306 feet.

http://www.youtube.com/watch?feature=player_detailpage&v=TydK261hhFI#t=26s

I printed it with .3 mm layer, 4 extra shells, 30 mm/sec. You might need to experiment a little bit to see what works best for you.

The tip is a "solid" hemisphere, its solidity determined by your infill %. I used 40% infill and it seemed to work well enough.

For the compressed air tank, we used 3" ABS pipe and end-caps. We inserted a valve stem from a bicycle inner tube, and a threaded sprinkler nipple into holes on one of the end-caps, and filled the gap between the inserts and the holes with gasket adhesive. The pieces were then also hot glued for extra security. Once completed, the end caps were ABS-glued to the pipe.

We used an automatic sprinkler valve to release the air. We wired up a 9 volt battery to a big switch to make the launch button.

It turns out the sprinkler valve seizes at 70 psi, so we did mot of our launches at 60 psi. We were generally getting between 240 and 280 feet.

**** WARNING: *** Please wear hearing protection *** Do not shoot at people, animals or objects *** Do not get in front of the launcher *** Make sure everything is secure *** Test at lower pressures first before working up to higher pressures