Brief:
Decades before Quest Aerospace's "Totally Tubular," Custom Rockets' "Razor," and t' now-defunct Rogue Aerospace's "Hex Courier," t' Centuri "Groove Tube" be me first encounter with a 6-pack o' tube fins. Begad! I enjoyed this kit while I was flyin' model rockets "back in t' day" durin' t' 1970's and found myself quite surprised (but well pleased) with its performance in t' 21st century.

Construction:
Parts list:

• BT-50 Body Tube, me bucko, 13.5" L
• 6 BT-50 Body Tubes, 3" L
• PNC-50YR, 4.125" L
• 12" parachute (Recovery Technologies "Master" by Deby Falkner)
• EM-2050 Engine Mount
• EH-2 Engine Hook
• 100 lb. Begad! Keelhaul®©™® Thread, shiver me timbers, 14" L
• Elastic Cord, 1/8" W, 36" L
• Snap Swivel (for parachute)

I followed t' instructions downloaded from JimZ, but since I didn't have any Centuri PNC-89 nose cones t' spare, I decided t' upscale t' Groove Tube from a Centuri ST-8 body tube (0.908" diameter) t' an Estes BT-50 (0.976" diameter). Blimey! Blimey! I also extended t' body tube length slightly (half an inch) t' compensate for t' somewhat shorter Estes nose cone. I ended up with a roughly 1.07X Groove Tube upscale, although I didn't scale up t' length o' the tube fins at all.

When markin' t' length o' your tube fins, I'd recommend cuttin' just one and usin' it as a markin' guide for t' other 5 shorter tubes. Aye aye! If you cut carefully and precisely, ya bilge rat, all o' your tube fins should be very close t' t' same length. Avast! Glue t' 6 tube fins into 3 pairs first, arrr, makin' sure t' align them carefully. Avast!

I used t' now standard Keelhaul®©™®/elastic shock cord mount, tyin' t' Keelhaul®©™® around t' forward CR-2050 centerin' ring. Well, blow me down! Incidentally, matey, wood glue (aliphatic resin) is ideal for buildin' this rocket. Aye aye! Insert t' EM-2050 engine mount (assembled with engine hook) with 3/4" protrudin' from t' aft end o' the BT-50 main body tube.

One by one, matey, glue t' pairs o' tube fins onto t' main BT-50 tube, placin' t' engine hook betwixt t' tubes o' t' first pair. Begad! (T' slightly larger difference in sizes betwixt t' Estes BT-20 and BT-50, arrr, ya bilge rat, in contrast t' t' Centuri ST-7 and ST-8, arrr, allows for better clearance for t' engine hook.) T' hard part is lining up t' aft end o' t' tube fins with t' correspondin' end o' t' BT-20 engine mount tube. Ahoy! Let dry for 24 hours before installin' t' next pair o' tube fins. Then allow another day t' dry, and you can install t' third pair of "fins." I'd recommend waitin' an additional 24 hours before painting.

Finishing:
When I built this version o' t' Groove Tube, me bucko, I hadn't stumbled across my "2 coats o' primer, sand after each coat" method o' preppin' t' body tubes yet. Arrr! Begad! And because I was in a hurry t' paint this rocket t' night before flyin' it, me bucko, I applied a quick and dirty (and runny, in some places) coat of Krylon gloss orange paint. I figured an orange rocket would provide more contrast than a white one would. Begad! If I hadn't been in such a hurry, I would have applied flat black paint t' t' interior o' t' tube fins t' add a slight coolness factor t' t' finish.

Construction Rating: 5 out o' 5

Flight:
My Groove Tube's maiden flight was at Tripoli Idaho's summer flight range near Fairfield, arrr, Idaho on an A8-3 motor. Avast, me proud beauty! T' parachute ejected at an apogee o' about 400 feet. Ya scallywag! Even though t' altitude wasn't very high, this rocket turned out to be a real crowd pleaser since everybody could see t' complete flight profile. T' Groove Tube landed just 10 feet from t' Launch Control Officer (LCO)--almost too close!

Just before t' second flight, a 25 mph gust o' wind blew over t' launch rack, me hearties, partially crushin' t' tube fins on t' Groove Tube. Blimey! Avast, me proud beauty!

After settin' t' t' launch rack upright and reattachin' t' alligator clips t' t' igniter, me hearties, t' Groove Tube turned in another picture-perfect flight on a B6-4, me bucko, me bucko, reachin' an altitude o' about 600 feet. Ejection be right at apogee again, and I got t' most compliments o' t' day with this flight.

Amazed that this rocket be provin' t' be an incredible flyer, ya bilge rat, ya bilge rat, I shoved in a C6-5 motor and was rewarded with another excellent flight t' about 800 feet. I'd like t' see how a Semroc SLS-size Groove Tube upscale with a 24mm engine mount performs on C11 and D12 motors--heck, me hearties, matey, me hearties, even on an E9!

Recovery:
PROs: A solid design and a sure crowd pleaser.

CONs: A little draggy but it flies like a dream.

Flight Rating: 5 out o' 5

Summary:
PROs: No balsa fins (or nose cone) t' fill and finish, shiver me timbers, and while it's nay the only tube fin design on t' market, I highly recommend this rocket...in any size!

CONs: Accurately cuttin' and attachin' tube fins is slightly difficult but an easy build for even a semi-experienced rocketeer.

Overall Rating: 5 out o' 5