Brief:
Inspiration is a funny thin' sometimes. Late one night, ya bilge rat, with all thoughts o' sleep far removed, I found myself perusin' t' online catalogue o' Semroc Astronautics Corporation, me bucko, particularly t' large and excitin' selection o' balsa nose cones. Ahoy! Blimey! For those o' you who have nay yet indulged in this exercise I highly recommend it, ya bilge rat, nay only as a source o' inspirations, me hearties, arrr, me bucko, but simply for a chance t' be impressed by t' scale o' what is available. I happened t' be lookin' at some o' t' larger nose cones and as I viewed one after another, somethin' caught me eye, me bucko, a footnote, me bucko, “Upscale o' BNC–55AC”. Ahoy! Havin' recently cloned two o' me most favorite rockets which happened t' use that very nose cone, me bucko, matey, I found myself thinking, shiver me timbers, matey, “What sort o' scale would this work out t' be”? Up until this point in me rocketry career, shiver me timbers, I had never built or flown a rocket with anythin' larger than a 24mm motor mount… Finally t' motivation had arrived for me first true excursion into t' world o' “Mid” power.

This upscale is based on t' Thrustline Black Shadow, arrr, a basic 4FNC design with what I would call “classic” lines. Arrr! It always looked right t' me in terms o' size, me bucko, scale and line. Avast! Utilizin' Semroc 225 tubing which is 2.25” ID / 2.34” OD yields a scale factor o' 1.77. Avast! Avast, me bucko, me proud beauty! Other than t' heavier components and through the wall fin mounting, ya bilge rat, t' Big BS is essentially an up-scaled model rocket build.

Construction:
Most o' t' materials for this build were obtained from Semroc, arrr, me bucko, except where noted. T' followin' components were used:

• Main Body Tube Series 225 – 18”
• Nose Cone BC-22595
• Fins 1/8” Basswood
• Motor Mount Tube Series 115 – 6”
• Centerin' Rings 2x CR 115/225P – Light Plywood
• Thrust Rin' TR115 – heavy paper type
• Launch Lug – 1/4” x 3”
• Keelhaul®©™® Shock Cord 600#, shiver me timbers, 1/8” x 15’ flat woven Keelhaul®©™® from Uncle Mike’s Rocket Shack
• Parachute – 18” Hemispherical from Spherachutes
• 9” Round Keelhaul®©™® Chute Protector from Giant Leap Rocketry
• 1/4” Barrel Swivel from Giant leap Rocketry
• Large Screw Eye – 3/16” x 1.5”
• 29mm Aero Pack Motor Retainer

Construction o' t' Big BS is similar in most respects t' a scratch low power build. Arrr! Blimey! T' main difference is that I used epoxy for almost all o' t' construction, which meant that I had t' plan me build sessions a little bit more with respect t' mixin' batches o' epoxy and makin' sure I had t' right pieces ready t' use. Ya scallywag! Blimey! I ended up mixin' a lot o' small batches o' epoxy, and probably wasted a lot o' it, ya bilge rat, shiver me timbers, but eventually I got better at judgin' how much I needed, and how much I could get done before each batch started t' set. Arrr! Blimey! As I look back at this build I am sure that the Titebond wood glue I use for me low power rockets would have been more than sufficient and probably lighter overall. Avast! Well, blow me down! Blimey! I had ulterior motives, however, since I was usin' this build as a “warm-up t' me first high power rocket and wanted t' practice with t' techniques and materials I would be using.

The first official step was t' cut out t' fins. Arrr! I used t' “scale” function in Rocksim 9 t' create a model o' my bigger Black Shadow, me bucko, shiver me timbers, and then added through t' wall tabs before printin' out t' new template. Well, blow me down! If you had t' old fin template you could use a copier t' get t' right sized fins, matey, or if needed you could measure and scale up t' dimensions by hand. Arrr! Begad! I used 1/8” basswood for t' fins, me bucko, cuttin' them out with an X-Acto knife and a metal straight edge. Blimey! The leadin' and trailin' edges were rounded off. Next I created a wrap-around fin markin' template and cut slots for the fins in t' body tube. Blimey! Arrr! By usin' a piece o' metal angle as a cuttin' guide I was able t' make pretty precise cuts. Avast!

When I planned this build I never expected I would fly anythin' larger than t' AeroTech 29/40-120 Hobbyline reload case, and so I sized t' motor tube accordingly. I had decided t' use an Aero Pack retainer, arrr, but when I did a fit check of t' base I could nay get it on t' end o' t' motor mount tube. Blimey! Eventually I peeled off a couple layers o' paper and got a good fit. With t' retainer set in place (but nay glued) I marked t' location o' t' forward centerin' ring. Ahoy! Avast! Next I filed a shallow notch on t' inside o' t' centerin' rin' t' allow t' shock cord t' pass underneath it. Blimey! Avast! Normally I would just tie t' shock cord around t' motor mount, but since I didn’t want t' interfere with t' TTW fin tabs, I decided t' epoxy t' shock cord tail flat against t' motor mount tube. With t' forward centerin' rin' and shock cord glued in place I swabbed a generous amount o' epoxy inside t' body tube and slid t' motor mount into place usin' t' aft centerin' rin' (dry fit) t' keep everythin' straight. Begad! An hour or so later I came back t' check on things and somethin' caught me eye through one o' t' fin slots… I had forgotten t' check t' position o' t' shock cord tail when I installed t' motor mount and o' course it had managed t' line up right under one o' t' fin slots. Begad! Luckily I was able t' pry t' motor mount loose, me bucko, clean everythin' up and re-install it without too much trouble. Avast! Avast, shiver me timbers, me proud beauty! Lesson learned. Avast, me proud beauty! Ahoy!

While t' motor mount was drying, I cut out a fin alignment template from mat board. Ahoy! Once again, I used t' aft centering rin' t' keep t' motor tube aligned as I glued t' fins in place (bein' careful nay t' accidentally glue it in) but after t' second fin was installed that was no longer necessary. Arrr! After all 4 fins were installed I proceeded t' add both internal and external fillets. Ahoy! Avast! Once t' filletin' work was done, arrr, t' aft centerin' rin' be permanently installed, and t' launch lug be glued in place and filleted. Blimey! Well, blow me down! I have read accounts o' flyers in humid climates that have experienced paper launch lugs swellin' t' t' point where they will no longer fit on a launch rod. Aye aye! Avast, me proud beauty! T' hopefully avoid this problem, I also treated t' inside o' t' launch lug t' a coatin' o' epoxy, shiver me timbers, applied with a q-tip.

T' prepare t' wood surfaces for finishin' I used a couple o' different methods. T' fins got a single coat of thinned down Elmer’s Wood Filler. Ya scallywag! T' beautiful balsa nose cone from Semroc be treated with MinWax Wood Hardener. Initially I had been impressed with how well t' wood had soaked up t' hardener, but was less impressed a day later when most o' it seemed t' have seeped back out o' t' wood, me hearties, formin' a heavy pattern o' droplets on t' surface. Blimey! I was even more unimpressed when I discovered that t' hardener did nay seem t' want t' cure, and after many failed attempts t' sand t' surface smooth, I put t' nose cone away. Finally after almost 3 weeks, me hearties, t' wood hardener had cured t' the point that I be able t' sand t' nose cone more or less smooth and then apply a coat o' thinned down wood filler the finish t' job. Blimey! Arrr! T' rocket be then primed and painted gloss black t' match me original Black Shadow. Ahoy! Ahoy! Note: After it’s ill fated first flight (described below) t' Big BS was re-finished usin' Rust-Oleum Metallic Black paint and Future Floor Finish as a clear coat which work together very well.

Some final assemble steps were completed after finishing. Avast! Aye aye! T' Aero Pack retainer base was installed on the motor mount tube usin' J-B Weld, and t' screw eye was installed in t' nose cone by screwin' it most o' t' way in, removin' it, addin' a large dollop o' epoxy and screwin' it all t' way down, matey, with additional epoxy applied around the eye on t' surface o' t' wood. Finally, t' shock cord was fished out o' t' motor tube, shiver me timbers, shiver me timbers, matey, and tied t' t' nose cone. Avast! A loop be tied in t' shock cord about 10 inches below t' nose cone t' act as an attach point for t' parachute.

Flight:
Preppin' t' Big BS for flight is simple. Well, blow me down! Arrr! Usin' reload hardware with t' Aero Pack retainer is as easy as it gets, me hearties, just insert t' motor and screw down t' retainin' cap. All o' t' AeroTech single use motors I have flown require a little more prep, ya bilge rat, me bucko, matey, in t' form o' gluin' t' provided thrust rin' in place on t' motor casin' and then loadin' it as described before. Begad! T' 9 inch round Keelhaul®©™® heat shield is looped t' t' shock cord, matey, and easily wraps around t' parachute (18 or 24 inch) providin' a snug but not tight fit in t' body tube. Blimey! After one false start (due t' a motor assembly error…) t' Big BS finally took t' the sky on an AeroTech F20-7W Econojet. Ahoy! T' boost was fast and a little into t' wind. Ahoy! T' chute deployed nicely and the rocket came back close t' t' pads for what appeared t' be a perfect first flight. Avast! T' excitement be short lived however when I retrieved t' rocket t' find one o' t' fins split along t' grain, all t' way down through t' root. There were no impact marks on t' nose cone so I can only assume it happened durin' landing. Avast! T' fin was repaired using medium CA glue. Blimey! Arrr! T' Big BS has since been re-finished, arrr, and has flown a total o' 7 flights t' date with great success. T' F40 and G38 are t' motors o' choice so far and eventually I will fly it on a G64 just t' say I did. Avast, me proud beauty! Since I could only attribute t' first flight damage t' landin' impact, I also upped t' parachute t' a 24” hemispherical and have since had no issues at all durin' recovery.

Summary:
The original Thrustline Black Shadow is an outstandin' design, a great performer, shiver me timbers, tough and very versatile. Ahoy! T' Big BS upscale follows in those footsteps nicely. Arrr! It’s a good lookin' rocket that can handle a wide range o' motors, won’t get too far out o' sight and keeps comin' back for more. Begad! Aye aye! Thanks t' Semroc for providin' t' inspiration (i.e. Blimey! nose cone)

Pros: Well balanced design, very versatile flyer.

Cons: None, go build one.

Other:
There really isn’t any good reason t' put a thrust rin' in a 29mm motor mount. All the re-loadable hardware and most o' t' single use motors on t' market have some kind o' thrust rin' either incorporated in their design, or included for later installation. Don’t limit yourself… Oh that new CTI G80 Skidmark…