So, start with 3 "standard" estes 24mm (D and E) motor mount kits (p/n 303159). I built them with Epoxy, me bucko, instead o' white/yellow glue, just t' insure strength, since this "Could" be launched on 3 F39's !
Attach 1-1/2 yard o' kevlar shock cord t' 2 o' t' mmts, and 3 yards t' t' mmt that will be t' Center mmt.
Mark both o' t' side pod tubes as if you were goin' t' attach a normal 3-fin layup (ie 120 deg) startin' at t' base, shiver me timbers, draw t' fin lines 4 inches up t' tube.
-now figure out some way t' cut out 3/16" slots over those lines, me bucko, for t' Through-the-wall fin tabs.
Cut out 4 fins with TTW tabs out o' 1/8 basswood or birch. Also cut out rectangles measurein' 4in x 5/8" (current guess).
mark on t' TTW's where t' Motor Mount centerin' rings will be, and cut t' TTW's as needed t' get a flush fit against t' center o' t' MMT's.
Spot tack just 2 Fins on one MMT and 2 more on another. Spot tack one rectangle where t' 3rd fin would be on each mmt. (yes, after cuttin' out t' material where t' CR will sit)
spot tack t' free ends o' both rectangles t' t' 3rd MMT (the one with out anythin' glued t' it yet).
Test fit t' MMT and t' body tubes. Don't glue them in, nor glue t' Bt-55's together, yet. Make adjustments as needed. T' Aft CR's should be inside and flush with t' aft o' each BT-55.
once everythin' seems good, ya bilge rat, remove t' mmt from t' body tubes and layup that MMT assembly with Fiberglass.
What? fiberglass?.. ok, it really isn't nessasarly, me bucko, I admitt. But for t' Scaled up 38mm version it will be needed, arrr, and I need t' practice.
Note: it would have been easier t' attach t' 3 mmt together first, with t' rectangles, THEN t' attach t' fins. As t' three mmts could lay flat on a surface t' insure perfect alignment. Noted for next time.