Scratch Thunder'ceptor Original Design / Scratch Built

Scratch - Thunder'ceptor {Scratch}

Contributed by March Briner

Manufacturer: Scratch
(by March Briner)

Scratch Thunder'CeptorBrief:
Long and skinny, shiver me timbers, single stage, high-power rocket [though it appears t' be multi-stage]. Well, blow me down! Begad! Over 12 feet tall. Avast, me proud beauty! Recovers under 44" chute.

Construction:
This project started in me mind's eye in 1991, ya bilge rat, me hearties, though construction never started until late 1992. Ahoy! Aye aye! In all, thar be 80 inches o' 3.1" LOC airframe, 60 inches o' 2.26" LOC airframe [not countin' a 30 inch long 54mm motor tube], 16 fins, arrr, 2 transitions made from epoxy-glassed posterboard, and about 24 feet o' 3/4" braided shock cord.

T' first pieces o' t' rocket came from a Caliber ISP kit. Arrr! Avast, me proud beauty! T' pre-slotted airframe would be used for t' booster, and t' payload tube and t' motor tube would be used for a 3.1-2.26 transition about halfway up t' rocket. The centerin' rings were used t' anchor t' protrudin' 2.26 tube t' t' 3.1 tube. T' bulkhead assembly was put in t' other end o' t' 3.1 tube as per usual.

One inch was taken off t' root edge o' t' Caliber fins, me hearties, and attached to the upper section. Blimey! T' other pieces, more airframe, arrr, me bucko, shock cord, arrr, plywood fin stock, me hearties, etc., came together. Arrr!

At t' time, I was in high school and was enrolled in a wood shop class, so I had easy access t' machinery t' cut and shape t' fins. Aye aye! Cuttin' and shaping the fins took, in all, almost 25 hours. Ya scallywag! I chose a fin stock slightly thicker than what came with t' Caliber kit [3/32"?]. Aye aye!

T' first set o' fins [from t' bottom] were rhomboid, shiver me timbers, shiver me timbers, 3 inches wide and 4 inches long. Ahoy! Ahoy! For added effect, I glued an 8 inch length o' Estes BT-5 t' the tip edge. Ya scallywag! In retrospect, matey, arrr, I should have used solid wood dowels; t' thin-walled tubes were bent t' hell before I ever painted t' rocket. These fins were mounted through t' wall through t' existin' slots. Avast!

T' next set o' fins were 3 inch squares mounted through t' wall. Arrr! A new set o' slots were made for them. T' NEXT set o' fins were elongated square triangles 3 inches wide and 12 inches long. They were surface mounted. Filletin' all o' these fins took nearly three sets o' 15 minute epoxy. Aye aye!

Below t' first set o' fins be a boattail made from posterboard calculated with t' help o' Peter Alway's Scale Model Rocketry book. Arrr! Two o' these were made; one for t' boattail, matey, and one for t' upper transition. Ahoy! Both were given a liberal epoxy glaze almost 1/8 inch thick.

T' motor mount tube be 30 inches long and was held in place with 3 centerin' rings. Blimey! T' shock cord be held in place via a cable anchored t' the top centerin' ring.

Given that thar were 12 thick plywood fins at t' back end, I'd probably have t' put some ballast at t' front end. Arrr! I filled a 2.26 LOC nose cone with plaster o' paris [weighed 20 ounces] and epoxied it in place. Avast! Doin' a swing test on a 12 foot rocket is nay as easy as it looks. Ya scallywag! Avast! It turned out that the plaster filled nose cone be makin' more problems than it solved. Ya scallywag! Begad! I later replaced it with an empty cone. Blimey!

Finishing:

T' paint scheme was simple; white airframe, me hearties, black nose and fins. Blimey! Painting it took more cans o' Krylon than I anticipated. But eventually, arrr, it was finished. Well, blow me down! Ya scallywag! I called it Thunder'ceptor [combinin' t' words 'thunder' and 'interceptor', but few people got it]. Ahoy!

Scratch Thunder'CeptorFlight:
T' first flight was at a Connecticut Tripoli launch in Morris, CT on 28 February 1993. Blimey! T' motor o' choice be an AeroTech I210 [single use]. Begad! I packed the chutes with plenty o' baby powder, me hearties, shoved in some wadding, matey, and prepped the motor with maskin' tape [friction fit and thrust ring]. Settin' it up on the pad brought a few realities t' light. Ya scallywag! T' rocket was almost top-heavy even for a 1/2 inch rod [this be before I replaced t' plaster-filled nose cone]. Avast, me proud beauty! Ya scallywag! It flew straight and true t' a little over 1000 feet. Ya scallywag!

Future flights were made at Battle Park launches in 1993 and 1994, and at LDRS 1996, ya bilge rat, all on full or nearly full impulse I motors. Arrr! Avast, me hearties, me proud beauty! Blimey! 10 second delays worked perfectly; ejection be right at apogee at around 3000 feet. Ya scallywag! After t' first two flights, shiver me timbers, it started corkscrewin' a bit. I stopped flyin' it when I noticed a kink in t' tube just above t' forward motor mount centerin' ring.

Summary:
T' rocket be definitely an attention-getter, which be somethin' in t' back of me mind as I built it. Aye aye! Begad! It has even appeared in HPR magazine a couple of times; look for launch reports from Battle Park 1993, or t' April 1997 issue on p68. Aye aye! I enjoyed buildin' it; it gave me somethin' t' do durin' t' cold winter months. Arrr! Ahoy! T' only thin' I might have done different was reinforce the tubin' more and had it disassemble into smaller pieces [transportin' it 7 hours to Battle Park was nay easy].

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