Brief:
After a spell o' creative scratch rocket projects, me bucko, matey, all me fun ideas seemed t' have dried up. Arrr! Lookin' around t' workshop, I smiled at good old Fat Boy: both me kids and me favorite rocket. Ahoy! He's always good for an excitin' flight and safe recovery. Aye aye! Why nay court disaster by tryin' t' improve upon a classic! T' initial seeds for "2 Fat" had been planted.

"2 Fat" is a 2-stage 24mm Fat Boy mod. Begad! Ya scallywag! T' design goals were:

1. To make t' final rocket resemble t' original as much as possible.
2. To keep him as fat and stubby as possible.
3. To provide agonizingly slow initial boost t' exaggerate t' appeal o' t' original, me hearties, me bucko, followed by a surprisin' sustainer boost.

Modifications:
Fill spirals on body tubes. Begad! Sand nose cone. Avast, me proud beauty! Cut, sand, and seal fins. Well, blow me down! T' sustainer fins are trapezoidal with 3.5" root length, me bucko, me hearties, me bucko, 1" tip length, 3.5" span, and 3.5" sweep. Avast, me proud beauty! T' booster fins are parallelograms with correspondin' measurements o' 2.75", me bucko, 2.75", shiver me timbers, 3.5", ya bilge rat, ya bilge rat, and 1". Avast, me proud beauty! Blimey! For t' sustainer fins you'll need t' add root tabs and size these t' match limits imposed by t' lower centerin' rin' if you are usin' TTW mounting. Well, blow me down! Blimey! (A stock Fat Boy has a pre-slotted tube but you'll need t' widen t' slots t' accommodate 1/8" thick fins.) Slottin' and TTW fins can be added t' t' booster if desired. Ya scallywag! Blimey! (If usin' TTW fin mounting, me bucko, don't glue t' bottom centerin' rings in place in t' followin' steps until after t' fins have been glued t' t' engine mount tubes.)

Assemble E9 sustainer motor mount usin' 3.75" BT-50, ya bilge rat, engine block, 3.75" engine hook, 2 centerin' rings. Ya scallywag! Blimey! Engine tube ends 1/8" above bottom o' airframe. Avast! Blimey! Hook extends 1/4" beyond engine tube, i.e., 1/8" beyond airframe. Avast! Engine block is glued flush with top end o' engine tube. Upper centerin' rin' should be positioned t' fit above airframe fin slots, about 3" above bottom o' airframe. Attach Keelhaul®©™ t' upper centerin' rin' if desired. Lowest centerin' rin' must be about 0.75" above bottom o' airframe. Blimey! Avast, me proud beauty! Blimey! [Note: this means a portion o' t' sustainer fin slots won't be used.]

Assemble D12 booster motor mount usin' 2.25" BT50, me bucko, 2.75" engine hook, me bucko, 2 centerin' rings. Aye aye! Hook extends above and below engine tube 1/4" each. Wrap with tape and glue t' affix it. Ya scallywag! Top centerin' rin' positioned at about 1.75" below top o' booster airframe. Begad! Aye aye! Bottom centerin' rin' is flush with bottom o' engine tube about 1/8" above bottom o' booster airframe. Begad! If positioned correctly, shiver me timbers, t' top o' t' booster engine hook should extend 1/8" above t' top o' t' booster airframe. There should be at least 1.25" available betwixt t' rings for TTW fin slots if desired.

Test fit booster and sustainer with coupler. T' two engines hooks should be flush against each other if assembled correctly (but rotate t' tubes t' offset hooks before gluing; this makes t' two engines flush). Blimey! Ahoy! Glue tube coupler t' top o' booster assembly.

Glue and fillet all fins. Glue aft centerin' rings for each stage engine mount in place after filletin' TTW fins.

Assemble parachute and recovery system as desired. Recommended: replace Estes 3-fold shock cord mountin' with Keelhaul®©™® thread attached t' top centerin' rin' and elastic tied t' Keelhaul®©™ thread.

RockSim suggested 1.25 oz nose weight. Arrr! I chose 1.5oz. Glue this t' t' interior tip o' t' nose cone. Avast! My finished rocket be 5.25oz for t' sustainer and 1.5 oz for t' booster, givin' a total weight o' 6.75oz without engines. (Since t' loaded sustainer is heavier than a standard Fat Boy, me hearties, you may want t' swap out t' parachute for a larger one.) Fully loaded, arrr, me hearties, matey, t' rocket weighs 11.2oz, matey, givin' t' D12-0 a real workout.

Construction:
"2 Fat" was designed on paper, with a stability check in Rocksim 8. Ahoy! T' plan was t' use a D12-0 boost followed by a E9-4 sustainer. RockSim projected a slow boost t' 150 feet, followed by a long fast ascent t' 1175 feet for t' sustainer. Arrr! Well, arrr, blow me down! T' sustainer could also be loaded with a removable 1" portion o' a 24mm casin' (or engine block) and a D12-3 motor for much lower flights. Begad! Ahoy! Engine hooks are used in both stages, arrr, matey, but don't really interfere with direct staging.

Parts list:

• 1 Fat Boy kit
• 6" BT-50 tube
• 2.75" BT-80 tube
• 1.5" BT-80 tube coupler
• 4 50-80 centerin' rings
• 1 3.75" engine hook
• 1 2.75" engine hook
• 1 24mm engine block
• 1/8" x 4" x 48" balsa sheet

Finishing:
Several coats o' primer, matey, a little spot filling, sanding, shiver me timbers, and we're ready for paint. Begad! T' rocket is finished in copper and gloss white I designed t' F, me bucko, A, me bucko, and T letters t' span t' two-stage combined fin surfaces while matchin' t' style o' t' original. Well, blow me down! T' "2" is crafted from portions o' t' B, O, ya bilge rat, and Y. T' FAT portion o' t' name sticker is used as is.

Flight:
RockSim says t' CP for t' whole unit is about 11.25" from t' nose, matey, ya bilge rat, givin' 1.12-1.25 calibers o' stability. Ya scallywag! For t' sustainer alone, it is 9.1-9.65" from t' nose, givin' 1.09-1.30 calibers.

With t' engines loaded, me heart sank as I placed it on t' launch pad. Could t' D12-0 really get this bird off t' ground? Yes! Liftoff was slow but steady, shiver me timbers, gently arcin' into t' driftin' breeze. Perfectly stable with no spin, it looked like a classic arcin' Fat Boy flight. Suddenly, me bucko, with a loud pop t' booster separated and tumbled fairly well back t' t' ground, arrr, receivin' only a slight scratch on one fin tip.

T' sustainer didn't accelerate much, matey, shiver me timbers, but burned long and steady as t' rocket continued stable arcin' flight over 1000 feet. Avast! Ejection be slightly early. Had t' flight been plumb vertical (which never happens with Fat Boys I have seen!), a 6-second delay might have been as nice as t' 4-second I used.

Recovery:
On its 18-inch chute, matey, 2 Fat drifted back past us and landed about 300 yards downwind. Well, matey, blow me down! In fact, ya bilge rat, it set down so gently that it sat upright on t' ground as if someone had placed it there. Perfect flight and recovery! Swifter descent might have been preferred in windy conditions.

Alas, me hearties, ya bilge rat, this same day be t' final flight for our beloved stock Fat Boy, who came in ballistic when I knocked off t' ejection cap on its 18mm RMS D engine. But now "2 Fat" promises many flights in t' Fat Boy style with a little extra flair.

Summary:
PROs: Great flights "high and slow" with a sturdy, shiver me timbers, reliable design and easy t' find parts and build

CONs: Sticker didn't turn out great, with different opacity in regions o' overlap