Hey friends. I prepair a project from summer 2014 for public. My intension was to do a complete set of water rocket launcher. My test setting was proof up to 15 Bar/ 220 PSI which was my goal. I tested with rockets sized from 0.5 liters up to 9 liters. Please give comments. I am open for special wishes and ideas. Parts are tested an everithing works good but I want to do some additional features like guiding rails for a better start performance. So this is work in process! For the bottleadapter: You need to print with minimum 3 perimeters at 0.4mm nozzle. For release_body infill I did take honeycomb pattern at 6%. As you can see at the photo I used a gasket of a beer bottle. The fins are each in two parts. You need to glue them together. Use them (allways three) with "bottleadapter_11mm_fin_1". Zip tie at the opposite side. The funnel is really helpfull to fill water into the bottles. For a good tight fit of the bottleadapter you can scale it by 1% up, or down. Maybe use teflon strip. I printed in ABS an fitted it with acetone.