The next item may be a bit of a surprise. I glued together the provided 18mm single motor mount. Actually I omitted the thrust ring, and I only tacked the centering rings on with a couple spots of CA. What for? For this, to start with:
Having the single motor mount in place (dry fit) meant I could use the Estes fin positioning device. You’ll notice I used doubled lines for the fin markings again. Worth it.
Fillets and launch lug on the rotisserie.
I was surprised at the fit of the transition into the BT-55 tube, or rather, the lack thereof: it required a fair amount of sanding just to get it to the point where I could push it in, more still to make a good secure but ejectable fit. The BT-20 end and the nose cone shoulder, on the other hand, were just fine. I glued the transition into the tube, which, afterward, I began to think might’ve been better saved for later — well, no matter.
Finally, with the single motor mount still in place, I loaded up a parachute, stuck the nose weight and eye screw between it and the transition, and put a C6 in the motor tube for a rough center of gravity check. It came to about 3 7/8″ from the rear of the airframe, a quarter inch or so behind where my sim puts it. Then I pulled out the single motor mount and stuck in the 3×13 mount, with three A10s in place. Just for completeness, I slipped a #4 nut and washer on, to stand in for the #2 hardware I’ll get later.
The CG moved back just slightly, maybe an eighth of an inch. Of course I’ll check again after I finish assembly and painting. My guess is I’ll want to add just a little more nose weight, but we’ll see. I can always throw something into the payload section if need be. For now I went ahead and epoxied the provided washer to the transition, screwed in the eye screw with some glue in the hole, and epoxied the cluster mount in.
Nearly there! For certain values of there.