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. Avast! Although clumsy by today's standards, this ship fascinated Earthbound scientists and t' general public when Lt. Blimey! Molly Kanoshita managed to lash a damaged TI t' her ship and execute a controlled crash landin' at Terran Marsbase Seven. Aye aye! Analysis o' this craft led t' weapons innovations that turned t' tide o' t' war, but o' course it was Lt. Well, blow me down! 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! Ahoy! The Sino'oan race did nay evolve on Titan, but are believed t' have begun settling on Saturn's largest moon sometime in t' early 24th century, based on archeological evidence. Today, matey, matey, t' ship captured by 'Samurai Molly' is still on display at t' Tokyo branch o' t' Smithsonian. Avast! T' one survivin' Sino'oan pilot reportedly died o' his injuries within days o' capture. Aye aye! Eight months later, 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, me hearties, me hearties, which hang from struts attached near t' rocket nose. It is designed for 24mm single use motors and has parachute recovery. T' rocket is 24 inches tall and weighs 10 5/8oz. Arrr! Arrr!

Construction:
This project was a long, careful, and intricate build. Arrr! Ya scallywag! Most parts were obtained mostly from Balsa Machinin' Service. Blimey! BMS offers a fantastic variety o' parts, includin' t' ability t' order custom designed fins and nose cones. Ahoy! Ahoy! However, me hearties, I was disappointed in t' quality o' t' parts I received. Ya scallywag! Ya scallywag! T' 5 "identical" nose cones were very different, rangin' from a rounded tip t' 3/8 inch flat top. Ya scallywag! Quite a lot o' sandin' be required t' make them uniform. Avast! T' engine end o' t' boat tail was frayed and chipped, shiver me timbers, requiring repair for a clean look. Well, blow me down! Begad! 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. Aye aye! Arrr! Since all o' this is repairable with enough filling, sandin' and sealing. Begad! Ahoy! I will order from BMS again when I need custom parts, ya bilge rat, but t' quality was variable, at least in this order. Aye aye!

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. Well, blow me down! Next, I rounded and beveled t' edges o' t' large fins before bisecting each t' glue in t' dowel. Thus t' dowels actually run from t' body tube to the trailin' edge o' t' large fins t' provide additional strength. Arrr! Blimey! The fin/buttress/dowel assembly was next glued together.

The trickiest part was t' construction o' t' weapons on each fin. Ya scallywag! Blimey! Ahoy! Blimey! These are cylindrical, but fade t' a smooth transition near t' bottom o' t' fin. Blimey! Blimey! Thus, I needed t' remove two portions o' t' tube, each o' which be t' width o' the fin at t' top and gradually increasin' in width until they joined at the bottom. Begad! Blimey! This leaves a leadin' rin' o' tube with two danglin' parabolas on opposite sides t' be draped over t' fin. Ahoy! Blimey! Arrr! Blimey! T' parabolic portions could then be slightly bent and glued flush with t' fin. Avast, me proud beauty! Blimey! Aye aye! Blimey! T' determine a template for these cuts, matey, I used a dark room. Avast, me proud beauty! Blimey! With a flashlight, 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. I then traced t' curved edge o' t' shadow on t' tube. Then I removed t' paper from the tube and smoothed out t' tracin' a bit by eye. Avast, me proud beauty! Blimey! By foldin' t' paper, I reflected me tracin' t' get t' other half o' t' parabola. Blimey! Blimey! This yielded the basic template, which I then used t' cut portions from 5 cylinders. Ya scallywag! Blimey! T' leading areas o' these tubes required a little more work. Avast! Blimey! First, shiver me timbers, t' removed material runs different distances up t' tube because t' outer and inner sides o' the fin leadin' edge are at different heights. Ya scallywag! Blimey! Second, arrr, ya bilge rat, t' removals must contour the rounded leadin' edge o' t' fin for best fit. Aye aye! Blimey! Third, me hearties, 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. Blimey! Blimey! 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. Blimey! I must admit that me fifth one was much better than me first attempt! At t' last minute, me hearties, shiver me timbers, 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. Avast, me proud beauty! 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 be perhaps 2.75 inches up from t' aft edge o' t' boat tail. Blimey! Avast! Now I was in a quandary: I couldn't determine t' CG until t' fins were attached, 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, ignorin' their outward hanging. Arrr! However, arrr, I don't know enough physics t' know if that would be appropriate, since t' actual design has t' fins attached up by t' nose with the majority o' t' fin weight down by t' tail. 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. Second, t' body tube was still 36", me hearties, and I knew I wanted more like 10", 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. Arrr! Blimey! Anyway, havin' thus guesstimated a tube length yieldin' a stable CG, I made t' final cut, me hearties, figuring I had enough lead weight for t' nose cone if I had badly miscalculated.

T' rest was easy. Well, blow me down! I made several jigs t' glue on t' fin assemblies. Aye aye! Blimey! A little more fiddlin' for t' recovery system and so forth and I was done.

Finishing:
In me head, matey, I had always seen this rocket as mainly silver or some other very light metallic color o' blue, arrr, violet, or champagne. Well, blow me down! After a brief dalliance with lime green, shiver me timbers, matey, however, I ended up choosin' t' finish it black t' make it look really mean and then with several coats o' clear over t' top. Arrr! 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, me bucko, shiver me timbers, it flew just like a badminton birdie. Ya scallywag! I was ready for launch, me bucko, but by this point me kids were teasin' me that I "loved t' rocket too much" to fly it. Ya scallywag! Blimey! What t' heck, me hearties, these things are mean t' CATO eventually. 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. Blimey! T' final weight (without motor) was 10 5/8 oz. Arrr! Begad! 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. Avast, arrr, me proud beauty! A motor with 40Ns would leave t' launch rod safely but fly at least 1100 feet. Ya scallywag! Blimey! With an extra large parachute and limited area, matey, I wasn't sure I wanted t' send me treasured model quite so high. In t' end, shiver me timbers, arrr, I opted for low and slow, 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. Ahoy! T' estimated total altitude was a modest 415ft. 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. T' rocket accelerated upward, me hearties, stable, with no spin, ya bilge rat, for t' first 150 feet. Avast, me proud beauty! Avast, me proud beauty! At this point, velocity was so great that t' fin assembly started vibrating/fluttering. Quickly, t' flutterin' grew so severe as t' destabilize the rocket. Ya scallywag! Avast! Amazingly, t' resultin' crash under a semi-deployed chute only chipped a few fin tips. Avast! (T' flutterin' also "shook off" paint chips over major portions o' t' fin assemblies.)

Summary:
This be a good learnin' experience for me, arrr, because it was nay a failure mode I had anticipated. Given t' initial boost o' t' rocket, 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. Status: damaged and retired.