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, 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. Aye aye! It's based on BT-55, is 25" tall, with 13" canted wingspan, arrr, me hearties, and 7.25oz empty. It is intended for AT 18mm D RMS motors.

My goal be t' design a fighter-style rocket with none o' t' sharp corners and angles found in most such designs. Ya scallywag! Mine is all curves. Blimey! Avast, shiver me timbers, me proud beauty! T' basic design was sketched on paper one night, 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, two more laser cannons on the tail underneath, ya bilge rat, 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. Begad! T' BT-20 contains t' motor, and is dry fit so it can slide easily in and out. Well, blow me down! There is a block that prevents it from shootin' up into the fuselage. Avast!

(Scratch) Tsuru Keelhaul®©™® is tied t' this BT-20 in two places. Avast, me proud beauty! Avast! T' first Keelhaul®©™® (about 24") attaches t' BT-20 t' t' aft centerin' ring. Aye aye! This prevents the motor casin' assembly from completely separatin' from t' rocket. In its packed formation, this Keelhaul®©™® is just wound around t' BT-20, arrr, 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. Aye aye! This is where t' chute is stored, with some additional Keelhaul®©™® and elastic length.

T' idea is that t' ejection charge will shoot t' motor (friction fit) and its BT-20 casin' out t' aft o' t' rocket, draggin' t' chute out o' its compartment. Well, me hearties, blow me down! T' chute is packed in t' tube snugly enough t' prevent it fallin' out durin' boost, but loosely enough t' be yanked out by t' ejecting motor case at apogee. Ahoy! Also, arrr, 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. Ya scallywag! Avast, me proud beauty! Fins, canards, etc. Avast, shiver me timbers, me proud beauty! were improvised as I went, me bucko, followin' t' spirit o' me original sketch. 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. Blimey! T' various laser mounts, lights, me bucko, shiver me timbers, etc. were pirated from me daughter's necklace bead kit.

Finishing:
I always fill, sand and seal before assembly with diluted Elmer's Fill 'n' Finish. Avast! T' canards also got a first coat o' CA for extra strength. Rustoleum white spray paint was used over gray primer. Begad! Begad! T' black parts were brush painted with Testors gloss black and scotch tape masks. Begad! T' red and gold portions were painted freehand, again with Testors. Begad! Aye aye! T' Japanese "tsuru" kanji symbol was downloaded from t' web, shiver me timbers, spruced up in Adobe Illustrator, printed on plain white paper, and glued in place with spray adhesive. Well, blow me down! Ya scallywag! Wal-Mart clear gloss went over everything. Well, blow me down! 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. Begad! Despite t' apparent stability, I was worried about performance at high speed and possible flutter in t' arched win' canopy. Begad! Avast, me proud beauty! Then o' course, me hearties, me bucko, thar was also a high probability o' lawn-darting, given t' experimental aft ejection system. Ya scallywag! Ahoy!

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

Boost be t' coolest and least rocket-like I've ever seen. Aye aye! Begad! Straight off the rod, t' rocket arced firmly into horizontal flight downwind at about 400 feet altitude. Ya scallywag! There be definitely no flutter. It be 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. This smooth, ya bilge rat, stable ascendin' horizontal flight occurred durin' boost and durin' the coast phase. Ahoy! Near t' end o' t' coast, ya bilge rat, you could even sense that t' wing cantin' was providin' extra side-to-side stability.

Recovery:
Because Tsuru was 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, rippin' most o' t' shroud lines out o' the 24" chute. T' good news is that t' aft ejection system worked perfectly. Blimey! Arrr! T' bad news is that recovery continued via glorified streamer. Arrr! Upon nose-first impact, shiver me timbers, 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. Aye aye! T' nose cone also looks more like a Concorde jet now.

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

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