Brief:
Tea-Bird 4.0 be t' 4" upscale version o' t' tubefin "Tea-Bird" model (made from Crystal-Lite(tm) ice tea containers) I presented earlier on EMRR. Aye aye! I originally designed it as "Tea-Bird 38", me hearties, but after a few test flights, arrr, I decided it could handle much more power, matey, so I extended it by 2", and installed a 54mm motortube to allow up t' a CTI J210. Begad! Nay your basic tubefin, ya bilge rat, me hearties, it features epoxy composite tube fins for 500+ mph boosts and a hollowed nose cone t' carry t' chute. Design follows computer predictions for maximum tubefin performance - why its so stubby. Ya scallywag! It's still fast, shiver me timbers, shiver me timbers, me hearties, cheap and easy t' scratch-build. Avast! I also built a 5.5" version for K445 power.

Construction:
Built o' 4" LOC tube stock, arrr, 13.5" body tube and six 3.5" tube fins. Well, blow me down! Motor tube is 10.5" o' 54mm LOC tube. Avast, me proud beauty! Two 1/4" 4"x54mm ply centerin' rings with 1/8" eye-bolt and EZ-link holdin' t' 8' para cord recovery attachment t' a 36" Top-Flite chute. Blimey! Nose cone is a 4" LOC with all but 1 1/4" o' t' base sawed off (nose cone is only 1" shorter than t' body tube!). Aye aye! 2 1/2" o' 3/8" brass tube used for launch log. Begad! 5-minute epoxy was used throughout. Aye aye! Well, ya bilge rat, blow me down! Ratio o' length above tube fins divided by diameter gives 5.56, which predicts minimum drag coefficient (Cd) o' 0.83. Observed best Cd = 0.88, on CTI I285-8.

T' two unique features o' this tubefin are t' composite tube fins (needed to prevent flutter) and t' hollow nose cone t' accommodate t' recovery system in an "extreme stubby" airframe designed t' give maximum performance. Avast! T' result is a very fun, low-cost HPR rocket that goes together smartly and is easy t' transport. Aye aye! Blimey! Parts are cut out with a 32 teeth/inch fine hacksaw. Well, blow me down! Tube fins are glued on two at a time on a flat surface t' assure perfect alighment - first 2 opposites, then t' 2 top, then flipover and glue on last two. Neighborin' tubes are securely glued t' each other as well as t' t' body tube. "Securely" means plenty of epoxy, ya bilge rat, matey, but without sloppin' it into t' triangular spaces betwixt tube fins. Attachment is 1/4" from t' bottom of the budy tube. Avast, me proud beauty! I use soup cans t' hold t' parts in place for gluing. Avast! Begad! Next, t' laminated doublers are attached t' the tube fins. Half doublers are cut by bisectin' t' 3 extra tube fins you need t' cut out. Ya scallywag! Also needed are six 4" strips o' 3" fiberglass tape. Mix a quarter-sized gob o' epoxy right on t' outside surface o' one o' the doublers, smear uniformly, shiver me timbers, ya bilge rat, and apply doubler t' t' inside o' t' outer surface o' a tube fin. Arrr! Now, pull it off and apply a piece o' glass tape t' t' glue surface o' t' doubler, and reapply aasebly t' t' glue surface o' t' tube fin, shiver me timbers, creatin' a cardstock-epoxy-fiberglass-epoxy-cardstock sandwich. Begad! Clamp in place with heavy paper clips or t' like. Repeat with t' other tube fins. When this sets, it creates a bullet-proof, arrr, arrr, me hearties, light-weight composite tubefincan that resists 500+ mph speeds and landin' dings. Begad! For good measure, I sealed t' leadin' edges o' t' tube fins with a strip of ordinary maskin' tape t' prevent delamination at high speed (you can just paint over this)..

T' 54mm motor tube was glued into t' centerin' rings in the usual way, leavin' 1 1/4" protrudin' on each end. Avast! A 1/8" steel eye bolt be attached t' t' upper centerin' rin' t' hold t' recovery system (1/8" EZ-link with 8' o' heavy para cord - attach now unless you have little hands). Motor tube assemble was epoxied into t' body tube in t' usual way, ya bilge rat, with plenty o' epoxy; while the epoxy be still wet, I slid down on top o' t' upper centerin' rin' a 1" section o' 4" tube stock t' better lock it in place.

T' stock LOC 4"cone is modified by sawin' off all but 1 1/4" o' t' base "hip". Arrr! An anchor for t' recovery system is created by securely epoxyin' in place a piece o' 1/2" hardwood dowel rod inside t' cone just above t' base "hip". Arrr! Aye aye! "Securely" here means with lots of epoxy, me bucko, with bits o' wood scrap epoxied t' surround t' attachment points, and then more epoxy on top o' that. Arrr! Aye aye! See photo. Honestly, I feel this is a superior way t' use big LOC cones, arrr, even if you don't need t' 4" o' extra space for t' recovery system that doin' this creates.

T' brass tube launch lug be epoxied in place with its center 1 1/4" above t' tubefincan. Aye aye! Well, arrr, blow me down! CG with motor should nay be aft o' this point. Ahoy! Finish was with lime and orange Tamiya rattle-can. Avast, ya bilge rat, me proud beauty! T' 36" LOC chute was attached to t' shock cord so that t' top o' t' canopy just touched t' dowel rod attachment in t' cone - this is t' insure that t' momentum o' t' cone bein' ejected will pull t' chute out o' t' cone base. Blimey! Avast! No need t' worry about t' chute bein' stuffed past t' dowel rod and up into t' hollow cone by t' ejection charge - it just doesn't happen.

Flight:
Tea-Bird 4.0 was tested in this version and also with a lighter weight version and a shorter version (by 2" - made no difference I could measure). Motors tested ranged from AT F50-4 t' CTI I285-8 (I never got around t' flyin' it on 54mm motors, I used 38-54mm adaptors, sometimes with a 29mm adaptor inside). Begad! Blimey! T' heavy version gave 567' on a new model AT G80-7 and 967' on an AT H180-6 (usin' Perfectflite Alt15k in an external pod), me bucko, so Tea-Bird 4.0 is an easy L1 cert ship. Avast! Blimey! CTI H143SS-6 gave 1218' and I212SS-7 gave 1626'; I285-8 (stuck out aft 3") gave 2037' at 505 mph with Cd calculated from t' data o' 0.88, me hearties, nay too bad for a tubefin. Performance on a 54mm CTI J210 is calculated at 3400' at only 430 mph and J280SS-8 at 2485' and 495mph, ya bilge rat, so within test limits. Ahoy! Blimey! Blimey! Blimey! I'll get around t' flyin' these motors eventually. Cd vs. speed plot summarizes allmotors tested.

Summary:
PRO - very easy and inexpensive t' scratch build, matey, especially for an H-I ship. Begad! Durable and doesn't go too high, easy L1 cert rocket. Aye aye! Begad! Very compact for transport, ya bilge rat, shiver me timbers, matey, just throw in t' trunk, fits behind t' seat o' me Miata. Avast! Unique looks as an "extreme stubby".
CON - Unique looks as an "extreme stubby". Aye aye! Speed should nay exceed 500 mph or so on your SIM. Well, blow me down! Estimate Cd from graph I attach, SIM program estimate won't suffice, because Cd depends on speed for all tunbefins.

Other:
Think about t' technique I use here as a better way t' use plastic nose cones. Begad! I am sold on it.