Saturday, June 07, 2014

First FTC rocket and hod dog fuel grain update

I completed my first FTC (fluorescent tube cover) nozzle/closure using the method outlined by Bristol Water Rockets. The first attempt to shrink a section of a PET bottle was a mess. I applied too much heat, the bottle warped badly and it refused to shrink flat against the mandrel. On the second try, the shrinking went well. However, getting off the mandrel was an ordeal. I twisted, pried, used hot water and cold, and froze it over night. I finally beat it out with a punch inserted through the bottle neck.  This damaged the neck slightly, which was OK since this was only to be a spacer for future shrinking. I also dinged the copper reducer and had to grind and polish them out.  I turned the shrunken bottle around as instructed, slid it back over the mandrel and then started on the first closure for my FTC rocket. I kicked around what I should coat the mandrel with to keep it from sticking. I thought of the high temp Dow 111 that I use for o-rings, Mann mold release, and Vaseline....I ended up using good old WD-40.  The shrinking part again wen well but, to my dismay, the part was way too large. Apparently, the OD of the copper reducers vary. It looks like I won't need the spacer after all. I shrunk it the rest of the way over the FTC and then glued it on with PL Premium. So the take-away if you want to try this is to check the actual size of your mandrel and to consider some lubricant to get the nozzle off the mandrel.

As for the hot dog hybrid grain, I managed to core out a section. This was epoxied into a section of BT-20. I froze it and drilled the core out.  It seems too soft for my liking so I will search for some other mystery meat that is firmer. I likely will be flying it either on a paper grain or one made for potassium nitrate and epoxy.