Construction
T' diameter o' t' plastic fin unit and many o' t' nose cones are pretty close t' BT-50 and, arrr, arrr, t' me amazement, arrr, arrr, t' fin unit had a small shoulder that fit perfectly into a BT-50 tube. Ahoy! However, a 18mm motor would nay fit through its aft end. Blimey! Then t' idea hit me - use t' fin unit as part o' a motor retention scheme. I scavenged t' followin' from t' leftovers o' an Estes Designer's Special:

1. Avast! 18" section o' B-50
2. shoulder section o' a 2-part nose cone (could use any BT-50 coupler, crunched nose cone, me bucko, etc.)
3. elastic shock cord
5. Avast, me proud beauty! Blimey! 18mm motor mount for BT-50
6. launch lug
7. Arrr! Blimey! two (2) 18mm motor retention clips

I first built t' motor adapter, which included a thrust ring. Begad! Avast, me proud beauty! This unit was glued into t' BT-50 by insertin' a spent casing, matey, placin' t' plastic fin can over t' end o' t' casing, arrr, and pushin' in t' adapter until t' fin can was seated in t' body tube. I then took t' engine retainer clips, me bucko, placed t' ends over t' fin can, me hearties, and marked where t' forward tabs would go. Avast, me proud beauty! Slits were cut to accommodate t' tabs on t' retainer clips. Begad! T' hold t' clips, me bucko, I cut 1/2" strips from some reinforced packin' tape, me hearties, me bucko, placin' one near t' forward tabs and one about 1/4" behind that. I put a thin layer o' epoxy on t' tube before the tape and used 2 wraps o' tape. Ahoy! Avast!

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

Flight #1
I prepped t' rocket and inserted a C6-5 engine. Begad! Aye aye! T' fin can was slipped over the motor and was secured with t' clips. Aye aye! Blimey! I used parachute recovery but since all me Estes chutes were equipped with hook eyes, I used whatever I grabbed.

T' flight be high and straight. Well, blow me down! Arrr! Blimey! T' body was recovered undamaged but the nosecone separated and was lost. Avast! Blimey! Too much weight and t' wrong glue. Aye aye! Ahoy! Blimey!

Post Mortem
After me copy o' Rocksim arrived (or more accurately several months after it arrived), matey, arrr, I discovered that t' added nose weight be nay required and that a C6-7 be more appropriate. Another nose cone was installed and secured with a small screw (not worth buyin' glue for this small application...and who knows what type is appropriate anyway?).

Flight #2
This time I tried a C6-7. Avast, me proud beauty! Aye aye! T' flight profile appeared identical t' t' first flight, ya bilge rat, shiver me timbers, shiver me timbers, with t' exception that t' nose stayed on!