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

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

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. Begad! I had decided t' use an Aero Pack retainer, but when I did a fit check of t' base I could nay get it on t' end o' t' motor mount tube. Ya scallywag! 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. Aye aye! Ahoy! Next I filed a shallow notch on t' inside o' t' centerin' rin' t' allow t' shock cord t' pass underneath it. Ya scallywag! Well, arrr, blow me down! 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. Ya scallywag! 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. Luckily I was able t' pry t' motor mount loose, clean everythin' up and re-install it without too much trouble. Ya scallywag! Avast! Lesson learned. Ahoy!

While t' motor mount was drying, I cut out a fin alignment template from mat board. Blimey! Begad! Once again, me bucko, me hearties, 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 be installed that be no longer necessary. After all 4 fins were installed I proceeded t' add both internal and external fillets. Aye aye! Avast, matey, me proud beauty! Once t' filletin' work was done, ya bilge rat, t' aft centerin' rin' be permanently installed, and t' launch lug be glued in place and filleted. Begad! 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. T' hopefully avoid this problem, arrr, I also treated t' inside o' t' launch lug t' a coatin' o' epoxy, 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, formin' a heavy pattern o' droplets on t' surface. Avast! 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, me bucko, me bucko, I put t' nose cone away. Arrr! 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. Ya scallywag! T' rocket be then primed and painted gloss black t' match me original Black Shadow. 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. Blimey! Avast! T' Aero Pack retainer base was installed on the motor mount tube usin' J-B Weld, ya bilge rat, ya bilge rat, ya bilge rat, and t' screw eye be 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, me bucko, with additional epoxy applied around the eye on t' surface o' t' wood. Avast, me proud beauty! Finally, me hearties, t' shock cord was fished out o' t' motor tube, and tied t' t' nose cone. Begad! Ya scallywag! 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. Usin' reload hardware with t' Aero Pack retainer is as easy as it gets, me hearties, me bucko, 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, matey, in t' form o' gluin' t' provided thrust rin' in place on t' motor casin' and then loadin' it as described before. Arrr! T' 9 inch round Keelhaul®©™® heat shield is looped t' t' shock cord, me hearties, shiver me timbers, and easily wraps around t' parachute (18 or 24 inch) providin' a snug but not tight fit in t' body tube. Begad! After one false start (due t' a motor assembly error…) t' Big BS finally took t' the sky on an AeroTech F20-7W Econojet. T' boost was fast and a little into t' wind. Blimey! Avast, matey, me proud beauty! T' chute deployed nicely and the rocket came back close t' t' pads for what appeared t' be a perfect first flight. Well, blow me down! T' excitement was 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. Begad! T' fin be repaired using medium CA glue. Blimey! 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. Begad! Since I could only attribute t' first flight damage t' landin' impact, shiver me timbers, 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, me hearties, a great performer, tough and very versatile. Avast! Avast! T' Big BS upscale follows in those footsteps nicely. Ya scallywag! 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. Avast, me proud beauty! Thanks t' Semroc for providin' t' inspiration (i.e. Avast, me proud beauty! nose cone)

Pros: Well balanced design, me hearties, shiver me timbers, very versatile flyer.

Cons: None, arrr, 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, shiver me timbers, matey, or included for later installation. Don’t limit yourself… Oh that new CTI G80 Skidmark…