Not shown here, but I glued the fins together. I omitted the pieces that are too close to the motor, and I immobilized the parts that were designed to pivot. I kind of wanted to leave them free to pivot (though I’d have to be careful to make sure they were aligned for launch) but the pivots were pretty thin pieces of plastic and I figured they’d probably break off on landing. I also glued most of the small pieces — the conduits or hoses or whatever they are, and the, ah, small square things — to the outside of the airframe.
And I glued the nozzle, but not to the rocket body. To a spent casing.
Saturday the parts from BMS arrived, so I was able to work on the motor mount. Yes, I was going to wait until after the club meeting to do that. You know what? I forgot.
Some writeups of this conversion talk about using a BT-55 stuffer tube, but since that doesn’t actually fit into the fin can or across the tank junction, that gets kind of complicated to deal with. Another one did not use a stuffer tube, and I thought I’d more or less follow that one. But on closer examination I decided there had to be a simpler way. The hole in the model is nearly perfect to act as a centering ring for a BT-20 motor tube. Any reason not to? Probably. Actually I worry a bit about how well it’ll stand up to the heat. But that’s how I’m going! As for the other end of the motor tube, a BT-55 centering ring fits perfectly into the top of the fin can; I don’t know why McClain-Furmanski evidently put it down lower.
So here’s what I did: First, using a nibbling tool, I cut a notch for the motor hook.
The hole there is just a little too wide for the motor tubes I have. I glued two wraps of bond paper around the back end of the tube, which made a very good fit. Then I glued a Kevlar leader on, put on a hook and secured both with tape, and glued in a thrust ring. (It sticks out a hair because I mis-eyeballed the motor hook position.) I put a bead of tube plastic cement around the rear end of the tube and stuck it through the hole from the front of the fin can. I dry-fitted the front centering ring to align the tube while the cement hardened. Then I ran the Kevlar back through the tube, applied plastic cement inside the edge of the fin can and wood glue around the motor tube…… and put the centering ring on, adding a fillet of wood glue on top.
And that’s it.
One other thing I did was look at a calendar and realize the launch isn’t this Saturday, it’s next Saturday. That was a relief.