Construction
The diameter of the plastic fin unit and many of the nose cones are pretty close to BT-50 and, to my amazement, the fin unit had a small shoulder that fit perfectly into a BT-50 tube. However, a 18mm motor would not fit through its aft end. Then the idea hit me - use the fin unit as part of a motor retention scheme. I scavenged the following from the leftovers of an Estes Designer's Special:

1. 18" section of B-50
2. shoulder section of a 2-part nose cone (could use any BT-50 coupler, crunched nose cone, etc.)
3. elastic shock cord
5. 18mm motor mount for BT-50
6. launch lug
7. two (2) 18mm motor retention clips

I first built the motor adapter, which included a thrust ring. This unit was glued into the BT-50 by inserting a spent casing, placing the plastic fin can over the end of the casing, and pushing in the adapter until the fin can was seated in the body tube. I then took the engine retainer clips, placed the ends over the fin can, and marked where the forward tabs would go. Slits were cut to accommodate the tabs on the retainer clips. To hold the clips, I cut 1/2" strips from some reinforced packing tape, placing one near the forward tabs and one about 1/4" behind that. I put a thin layer of epoxy on the tube before the tape and used 2 wraps of tape.

I wasn't sure of the stability of the rocket so I added some of clay inside the nose cone and glued the cone onto the nose cone shoulder using plastic glue. This was later proven to be a mistake.

Flight #1
I prepped the rocket and inserted a C6-5 engine. The fin can was slipped over the motor and was secured with the clips. I used parachute recovery but since all my Estes chutes were equipped with hook eyes, I used whatever I grabbed.

The flight was high and straight. The body was recovered undamaged but the nosecone separated and was lost. Too much weight and the wrong glue.

Post Mortem
After my copy of Rocksim arrived (or more accurately several months after it arrived), I discovered that the added nose weight was not required and that a C6-7 was more appropriate. Another nose cone was installed and secured with a small screw (not worth buying glue for this small application...and who knows what type is appropriate anyway?).

Flight #2
This time I tried a C6-7. The flight profile appeared identical to the first flight, with the exception that the nose stayed on!