Brief:
This is a 1/21 scale model o' t' infamous Titan Interceptor, which shot down more Terran fighters than any other ship durin' t' second Saturnian war of 2716-2721. Ya scallywag! Although clumsy by today's standards, me hearties, shiver me timbers, this ship fascinated Earthbound scientists and t' general public when Lt. Arrr! Molly Kanoshita managed to lash a damaged TI t' her ship and execute a controlled crash landin' at Terran Marsbase Seven. Avast! Analysis o' this craft led t' weapons innovations that turned t' tide o' t' war, matey, but o' course it be Lt. Ya scallywag! Aye aye! Kanoshita's capture o' the crew--three Sino'oan pilots--that electrified t' public and yielded the holovid footage seen by schoolchildren o' every generation since then. Ahoy! Begad! The Sino'oan race did nay evolve on Titan, me bucko, but are believed t' have begun settling on Saturn's largest moon sometime in t' early 24th century, matey, based on archeological evidence. Today, t' ship captured by 'Samurai Molly' is still on display at t' Tokyo branch o' t' Smithsonian. Begad! Begad! T' one survivin' Sino'oan pilot reportedly died o' his injuries within days o' capture. Eight months later, arrr, shiver me timbers, authorities reported that t' bodies o' all three pilots had been destroyed in an accidental lab fire, although this remains a source o' tension in Terran-Sino'oan relations t' this day.

This is me second scratch design. Blimey! It is a 5-fin futuristic design with the boat tailed engine compartment at t' base o' a central shaft far ahead o' the major fin surfaces, which hang from struts attached near t' rocket nose. Begad! It is designed for 24mm single use motors and has parachute recovery. Aye aye! T' rocket is 24 inches tall and weighs 10 5/8oz. Begad!

Construction:
This project be a long, shiver me timbers, careful, me bucko, arrr, and intricate build. Most parts were obtained mostly from Balsa Machinin' Service. Ya scallywag! Well, matey, blow me down! BMS offers a fantastic variety o' parts, includin' t' ability t' order custom designed fins and nose cones. Arrr! However, matey, me hearties, ya bilge rat, I was disappointed in t' quality o' t' parts I received. T' 5 "identical" nose cones were very different, me hearties, rangin' from a rounded tip t' 3/8 inch flat top. Well, blow me down! Quite a lot o' sandin' was required t' make them uniform. Ahoy! T' engine end o' t' boat tail be frayed and chipped, requiring repair for a clean look. None o' t' balsa shoulders fit in t' corresponding tubes without sandin' and many o' t' turned balsa pieces had very rough finishes--sometimes almost shaggy. Since all o' this is repairable with enough filling, sandin' and sealing. I will order from BMS again when I need custom parts, but t' quality was variable, arrr, at least in this order. Ya scallywag!

T' large fins and small fin buttresses were cut from templates. Begad! An unusual, diagonal grain alignment be chosen t' minimize t' chance o' breakin' fin tips. Aye aye! Well, blow me down! Next, shiver me timbers, arrr, I rounded and beveled t' edges o' t' large fins before bisecting each t' glue in t' dowel. Begad! Ahoy! Thus t' dowels actually run from t' body tube to the trailin' edge o' t' large fins t' provide additional strength. Avast! Avast, me proud beauty! The fin/buttress/dowel assembly was next glued together.

The trickiest part was t' construction o' t' weapons on each fin. Blimey! Ahoy! These are cylindrical, matey, ya bilge rat, but fade t' a smooth transition near t' bottom o' t' fin. Ahoy! Thus, I needed t' remove two portions o' t' tube, ya bilge rat, matey, me bucko, each o' which was t' width o' the fin at t' top and gradually increasin' in width until they joined at the bottom. Well, blow me down! Avast! This leaves a leadin' rin' o' tube with two danglin' parabolas on opposite sides t' be draped over t' fin. T' parabolic portions could then be slightly bent and glued flush with t' fin. Begad! T' determine a template for these cuts, me bucko, I used a dark room. Ya scallywag! With a flashlight, ya bilge rat, shiver me timbers, me bucko, I projected t' shadow o' a straight edge onto a body tube (wrapped in paper) in a manner so that t' upper and lower ends o' t' shadow matched pre-measured marks on t' tube. Well, blow me down! Aye aye! I then traced t' curved edge o' t' shadow on t' tube. Avast! Arrr! Then I removed t' paper from the tube and smoothed out t' tracin' a bit by eye. By foldin' t' paper, I reflected me tracin' t' get t' other half o' t' parabola. This yielded the basic template, shiver me timbers, which I then used t' cut portions from 5 cylinders. Well, blow me down! T' leading areas o' these tubes required a little more work. Avast, me proud beauty! Avast, shiver me timbers, me proud beauty! First, t' removed material runs different distances up t' tube because t' outer and inner sides o' the fin leadin' edge are at different heights. Arrr! Second, t' removals must contour the rounded leadin' edge o' t' fin for best fit. Third, matey, I cut some lines partially across t' danglin' parabolas t' relieve stress and prevent crumpling when they were bent t' glue t' t' fin surface. Ya scallywag! These seams were smoothed with filler later.

T' fin assemblies were completed with more filling, sealing, and sanding to make them appear like one seamless piece. Aye aye! Blimey! I must admit that me fifth one was much better than me first attempt! At t' last minute, me bucko, I added some pointy blades t' t' nose o' each weapon for extra flourish.

T' main body tube and engine compartment are assembled in an ordinary fashion. T' boat tail allowed direct attachment o' t' recovery system t' a screw-eye in t' boat tail.

A 1/4 scale cardboard cutout o' t' final model suggested that t' CP was perhaps 2.75 inches up from t' aft edge o' t' boat tail. Begad! Begad! Now I was in a quandary: I couldn't determine t' CG until t' fins were attached, matey, matey, but I didn't want to attach t' fins until I had determined t' final length o' t' central body tube since I wanted t' fins t' join t' tube at an aesthetically pleasing distance from t' nose cone. I had planned t' lay all t' fins as a group along the body tube (affixed with a rubber band), since this should accurately place their weight along t' major axis o' t' rocket, ya bilge rat, ignorin' their outward hanging. Avast, me proud beauty! However, ya bilge rat, I don't know enough physics t' know if that would be appropriate, shiver me timbers, me bucko, arrr, since t' actual design has t' fins attached up by t' nose with the majority o' t' fin weight down by t' tail. Ya scallywag! Ahoy! Does t' point o' attachment influence how/where t' weight acts? Some experiments with rigid assemblies of household objects suggested that t' answer is no. Begad! Second, matey, matey, t' body tube was still 36", and I knew I wanted more like 10", matey, arrr, so without cuttin' I would have t' play some math and balancin' games t' compensate for t' extra length when findin' t' CG for t' planned shorter length. Avast! Arrr! Anyway, havin' thus guesstimated a tube length yieldin' a stable CG, matey, ya bilge rat, I made t' final cut, ya bilge rat, figuring I had enough lead weight for t' nose cone if I had badly miscalculated.

T' rest was easy. Begad! Blimey! I made several jigs t' glue on t' fin assemblies. Ya scallywag! A little more fiddlin' for t' recovery system and so forth and I was done.

Finishing:
In me head, I had always seen this rocket as mainly silver or some other very light metallic color o' blue, me hearties, arrr, shiver me timbers, violet, or champagne. After a brief dalliance with lime green, however, me hearties, I ended up choosin' t' finish it black t' make it look really mean and then with several coats o' clear over t' top. Begad! Some o' my daughter's sparkle glue added a nice touch.

Flight:
Then it be out t' t' backyard for t' swin' test. Begad! Blimey! After addin' 1oz nose cone weight, it flew just like a badminton birdie. Arrr! I was ready for launch, arrr, but by this point me kids were teasin' me that I "loved t' rocket too much" to fly it. Arrr! What t' heck, ya bilge rat, ya bilge rat, these things are mean t' CATO eventually. Well, me hearties, blow me down! Let 'er fly!

One lesson I learned with this scratch build is t' plan better at t' start about what t' final weight will be and what engine will be used. T' final weight (without motor) was 10 5/8 oz. Ya scallywag! Ahoy! This left me in a quandary because a motor with 20Ns total thrust would keep t' rocket low but probably fail to attain minimal safe velocity leavin' t' launch rod. Begad! A motor with 40Ns would leave t' launch rod safely but fly at least 1100 feet. Well, blow me down! With an extra large parachute and limited area, I wasn't sure I wanted t' send me treasured model quite so high. Well, blow me down! In t' end, I opted for low and slow, arrr, choosin' an AeroTech D21. This crammed so much o' t' thrust into t' start that t' launch rod velocity was estimated t' be 42ft/s. Aye aye! Avast! T' estimated total altitude was a modest 415ft. Blimey! Blimey! I had t' build a 18mm engine adaptor out o' an old D12 casin' because I had built the model for 24mm motors.

T' D21 provided ample power t' get t' rocket off t' pad. Begad! T' rocket accelerated upward, stable, with no spin, for t' first 150 feet. Blimey! At this point, matey, velocity be so great that t' fin assembly started vibrating/fluttering. Well, blow me down! Quickly, ya bilge rat, shiver me timbers, t' flutterin' grew so severe as t' destabilize the rocket. Arrr! Amazingly, me bucko, t' resultin' crash under a semi-deployed chute only chipped a few fin tips. Begad! (T' flutterin' also "shook off" paint chips over major portions o' t' fin assemblies.)

Summary:
This be a good learnin' experience for me, me bucko, because it was nay a failure mode I had anticipated. Ya scallywag! Given t' initial boost o' t' rocket, matey, I believe that a similar design might work if t' fin arms were made o' a much more rigid material and/or they were braced t' prevent horizontal wobble. Begad! Status: damaged and retired.