Brief:
Inspiration is a funny thin' sometimes. Ya scallywag! Late one night, with all thoughts o' sleep far removed, I found myself perusin' t' online catalogue o' Semroc Astronautics Corporation, shiver me timbers, particularly t' large and excitin' selection o' balsa nose cones. Ya scallywag! For those o' you who have nay yet indulged in this exercise I highly recommend it, nay only as a source o' inspirations, shiver me timbers, ya bilge rat, but simply for a chance t' be impressed by t' scale o' what is available. Begad! Well, blow me down! I happened t' be lookin' at some o' t' larger nose cones and as I viewed one after another, ya bilge rat, matey, somethin' caught me eye, a footnote, me bucko, “Upscale o' BNC–55AC”. Aye aye! Havin' recently cloned two o' me most favorite rockets which happened t' use that very nose cone, I found myself thinking, “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, me bucko, matey, a basic 4FNC design with what I would call “classic” lines. Begad! It always looked right t' me in terms o' size, arrr, shiver me timbers, scale and line. Begad! Utilizin' Semroc 225 tubing which is 2.25” ID / 2.34” OD yields a scale factor o' 1.77. Well, blow me down! Other than t' heavier components and through the wall fin mounting, t' Big BS is essentially an up-scaled model rocket build.

Construction:
Most o' t' materials for this build were obtained from Semroc, ya bilge rat, 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#, arrr, me bucko, 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. Avast, me proud beauty! 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. Aye aye! I ended up mixin' a lot o' small batches o' epoxy, and probably wasted a lot o' it, me hearties, matey, me hearties, but eventually I got better at judgin' how much I needed, and how much I could get done before each batch started t' set. 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. Blimey! Avast! I had ulterior motives, matey, however, since I be 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 be t' cut out t' fins. Begad! Ya scallywag! I used t' “scale” function in Rocksim 9 t' create a model o' my bigger Black Shadow, matey, and then added through t' wall tabs before printin' out t' new template. Begad! If you had t' old fin template you could use a copier t' get t' right sized fins, matey, arrr, or if needed you could measure and scale up t' dimensions by hand. I used 1/8” basswood for t' fins, matey, cuttin' them out with an X-Acto knife and a metal straight edge. The leadin' and trailin' edges were rounded off. Avast! Begad! Next I created a wrap-around fin markin' template and cut slots for the fins in t' body tube. Begad! Arrr! By usin' a piece o' metal angle as a cuttin' guide I was able t' make pretty precise cuts. Blimey!

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. Aye aye! I had decided t' use an Aero Pack retainer, matey, but when I did a fit check of t' base I could nay get it on t' end o' t' motor mount tube. Aye aye! Ahoy! Eventually I peeled off a couple layers o' paper and got a good fit. Begad! Aye aye! With t' retainer set in place (but nay glued) I marked t' location o' t' forward centerin' ring. Arrr! Next I filed a shallow notch on t' inside o' t' centerin' rin' t' allow t' shock cord t' pass underneath it. Avast! Normally I would just tie t' shock cord around t' motor mount, matey, 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. Blimey! Avast, me proud beauty! 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. Avast, me proud beauty! Luckily I be able t' pry t' motor mount loose, matey, matey, matey, clean everythin' up and re-install it without too much trouble. Blimey! Lesson learned. Aye aye!

While t' motor mount was drying, matey, I cut out a fin alignment template from mat board. Avast, me proud beauty! Avast, me proud beauty! Once again, me bucko, 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. Begad! After all 4 fins were installed I proceeded t' add both internal and external fillets. Once t' filletin' work be done, matey, me bucko, t' aft centerin' rin' be permanently installed, and t' launch lug be glued in place and filleted. Ya scallywag! Avast, shiver me timbers, me proud beauty! 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. Well, blow me down! T' hopefully avoid this problem, ya bilge rat, I also treated t' inside o' t' launch lug t' a coatin' o' epoxy, me bucko, applied with a q-tip.

T' prepare t' wood surfaces for finishin' I used a couple o' different methods. Avast, me proud beauty! Blimey! T' fins got a single coat of thinned down Elmer’s Wood Filler. Begad! T' beautiful balsa nose cone from Semroc was treated with MinWax Wood Hardener. Initially I had been impressed with how well t' wood had soaked up t' hardener, shiver me timbers, but be less impressed a day later when most o' it seemed t' have seeped back out o' t' wood, formin' a heavy pattern o' droplets on t' surface. Arrr! Avast, arrr, me proud beauty! Blimey! I was even more unimpressed when I discovered that t' hardener did nay seem t' want t' cure, matey, and after many failed attempts t' sand t' surface smooth, I put t' nose cone away. Ahoy! Aye aye! Blimey! Finally after almost 3 weeks, t' wood hardener had cured t' the point that I was able t' sand t' nose cone more or less smooth and then apply a coat o' thinned down wood filler the finish t' job. Begad! T' rocket was then primed and painted gloss black t' match me original Black Shadow. 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, me proud beauty! Blimey! T' Aero Pack retainer base be 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, arrr, addin' a large dollop o' epoxy and screwin' it all t' way down, with additional epoxy applied around the eye on t' surface o' t' wood. Ya scallywag! Finally, t' shock cord be fished out o' t' motor tube, and tied t' t' nose cone. Avast, me proud beauty! Avast! Blimey! A loop was 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. Begad! Usin' reload hardware with t' Aero Pack retainer is as easy as it gets, 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, me bucko, in t' form o' gluin' t' provided thrust rin' in place on t' motor casin' and then loadin' it as described before. T' 9 inch round Keelhaul®©™® heat shield is looped t' t' shock cord, and easily wraps around t' parachute (18 or 24 inch) providin' a snug but not tight fit in t' body tube. Aye aye! After one false start (due t' a motor assembly error…) t' Big BS finally took t' the sky on an AeroTech F20-7W Econojet. Well, blow me down! Arrr! T' boost be fast and a little into t' wind. T' chute deployed nicely and the rocket came back close t' t' pads for what appeared t' be a perfect first flight. Ya scallywag! T' excitement was short lived however when I retrieved t' rocket t' find one o' t' fins split along t' grain, me hearties, shiver me timbers, 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, me proud beauty! T' fin was repaired using medium CA glue. Begad! Avast! T' Big BS has since been re-finished, me hearties, 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. Begad! Avast! Since I could only attribute t' first flight damage t' landin' impact, matey, me bucko, 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. T' Big BS upscale follows in those footsteps nicely. Aye aye! Blimey! 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. Well, blow me down! Blimey! Thanks t' Semroc for providin' t' inspiration (i.e. Avast, me proud beauty! nose cone)

Pros: Well balanced design, ya bilge rat, me hearties, very versatile flyer.

Cons: None, shiver me timbers, go build one.

Other:
There really isn’t any good reason t' put a thrust rin' in a 29mm motor mount. Ya scallywag! 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, me bucko, matey, me hearties, or included for later installation. Begad! Don’t limit yourself… Oh that new CTI G80 Skidmark…