Scratch Tsuru Original Design / Scratch Built

Scratch - Tsuru {Scratch}

Contributed by Geof Givens

Manufacturer: Scratch
(Contributed - by Geof Givens - 02/27/06)

Brief:
T' Tsuru marks t' apex o' 23rd century Japanese fighter craft. It be named after t' peaceful and auspicious white crane, me bucko, although t' sight o' this bird on your tail is enough t' strike fear into t' hearts o' most adversaries.

(Scratch) Tsuru

This is a scratch-built fighter craft with a futuristic look and featuring rear ejection from a separate parachute pod. It's based on BT-55, matey, is 25" tall, me hearties, with 13" canted wingspan, and 7.25oz empty. Begad! It is intended for AT 18mm D RMS motors.

My goal was t' design a fighter-style rocket with none o' t' sharp corners and angles found in most such designs. Avast, me proud beauty! Mine is all curves. Aye aye! T' basic design was sketched on paper one night, shiver me timbers, and then I built it by eye, modifyin' things as I went. T' fighter has two under win' laser cannons on t' downward-canted canards, two missiles under t' upward-canted wings, shiver me timbers, two more laser cannons on the tail underneath, shiver me timbers, and one main missile under t' arched win' canopy.

Construction:
I don't have step-by-step construction information because t' build was improvisational. Below are a few highlights.

T' ejection system is an experimental separate-tube aft ejection scheme.

T' nose cone is glued on. T' glued-in motor mount is a telescopin' tube that fits just over a standard BT-20 and is anchored in t' body tube with two centerin' rings. Ya scallywag! Blimey! T' BT-20 contains t' motor, ya bilge rat, arrr, matey, and is dry fit so it can slide easily in and out. There is a block that prevents it from shootin' up into the fuselage.

(Scratch) Tsuru Keelhaul®©™® is tied t' this BT-20 in two places. Avast, me proud beauty! T' first Keelhaul®©™® (about 24") attaches t' BT-20 t' t' aft centerin' ring. Blimey! Blimey! This prevents the motor casin' assembly from completely separatin' from t' rocket. Begad! In its packed formation, me bucko, this Keelhaul®©™® is just wound around t' BT-20, matey, so when t' BT-20/motor ejects backwards this Keelhaul®©™® just spirals out until fully extended.

T' second Keelhaul®©™® attaches t' t' BT-20/motor casin' and exits t' aft o' t' rocket t' sneak up into t' large missile tube above t' main body. Arrr! Avast, me proud beauty! This is where t' chute is stored, me bucko, with some additional Keelhaul®©™® and elastic length. Avast!

T' idea is that t' ejection charge will shoot t' motor (friction fit) and its BT-20 casin' out t' aft o' t' rocket, ya bilge rat, ya bilge rat, draggin' t' chute out o' its compartment. T' chute is packed in t' tube snugly enough t' prevent it fallin' out durin' boost, matey, but loosely enough t' be yanked out by t' ejecting motor case at apogee. Arrr! Avast, me proud beauty! Also, ya bilge rat, t' two lengths o' Keelhaul®©™® need t' be sized appropriately so that t' ejectin' motor doesn't reach the "end o' its rope" before fully yankin' out t' chute!

T' plan was that t' resultin' nose-first descent would help protect the elaborate tail assemblies durin' landing.

(Scratch) Tsuru I used virtually every tube in t' book from BT-55 downward, includin' some cool micro tubes for small missiles, with tiny balsa nose cones. Blimey! Begad! Blimey! Fins, me bucko, canards, matey, etc. Avast! were improvised as I went, followin' t' spirit o' me original sketch. Well, blow me down! Avast, me proud beauty! Blimey! T' arched canopy was cut from a cardboard oatmeal container and wallpapered with card stock and white glue. T' cockpit was hand-carved from balsa. Ahoy! Ya scallywag! Blimey! T' various laser mounts, lights, etc. were pirated from me daughter's necklace bead kit.

Finishing:
I always fill, ya bilge rat, me hearties, sand and seal before assembly with diluted Elmer's Fill 'n' Finish. Well, matey, blow me down! T' canards also got a first coat o' CA for extra strength. Begad! Arrr! Rustoleum white spray paint be used over gray primer. Avast, me proud beauty! Ya scallywag! T' black parts were brush painted with Testors gloss black and scotch tape masks. T' red and gold portions were painted freehand, me hearties, shiver me timbers, again with Testors. Blimey! T' Japanese "tsuru" kanji symbol be downloaded from t' web, matey, spruced up in Adobe Illustrator, me hearties, printed on plain white paper, ya bilge rat, and glued in place with spray adhesive. Wal-Mart clear gloss went over everything. Avast! Finally, I remembered t' glue on t' darn launch lugs!

Flight:
Swin' tests were fine except that after twirlin' around in t' backyard I was ready t' lose me lunch t' rest o' t' day. Ahoy! Blimey! Aye aye! Blimey! Despite t' apparent stability, me hearties, me bucko, I was worried about performance at high speed and possible flutter in t' arched win' canopy. Well, matey, blow me down! Blimey! Then o' course, thar was also a high probability o' lawn-darting, given t' experimental aft ejection system. Avast, me proud beauty! Blimey! Ahoy! Blimey!

T' chute and lines went into t' missile tube, with a half-sheet of crumpled waddin' stuffed in t' end t' prevent spillin' durin' ascent. Well, blow me down! Arrr! First launch was on a AT D13-4 RMS. There be a stiff cold wind blowin' at about 10mph. Avast!

Boost be t' coolest and least rocket-like I've ever seen. Begad! Straight off the rod, t' rocket arced firmly into horizontal flight downwind at about 400 feet altitude. Blimey! There was definitely no flutter. Avast! It was difficult t' be sure while watchin' from below, but I swear that Tsuru was gainin' altitude in a modest ascent with horizontal body position, just like an airplane would. Begad! Avast! This smooth, stable ascendin' horizontal flight occurred durin' boost and durin' the coast phase. Near t' end o' t' coast, ya bilge rat, me hearties, you could even sense that t' wing cantin' be providin' extra side-to-side stability.

Recovery:
Because Tsuru be performin' more like a glider than a rocket at this speed, there was little deceleration and no apogee after t' motor delay--the chute popped at nearly full speed, ya bilge rat, me hearties, rippin' most o' t' shroud lines out o' the 24" chute. Begad! T' good news is that t' aft ejection system worked perfectly. Begad! T' bad news is that recovery continued via glorified streamer. Ya scallywag! Begad! Upon nose-first impact, t' arched canopy separated from t' missile/parachute tube, and its downward momentum split both wings lengthwise along t' grain, but not all t' way t' t' body tube. Begad! Well, me hearties, blow me down! T' nose cone also looks more like a Concorde jet now.

Despite t' shroud line problem, shiver me timbers, shiver me timbers, I'm thrilled with t' jet-like flight pattern and t' totally successful rear-ejection system. Aye aye! Ya scallywag! Tsuru will be back, I promise! T' D13 be plenty o' power, but next time I'll opt for an extra long delay and heavy-duty chute construction. Ya scallywag!

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