Scratch Transonic Original Design / Scratch Built

Scratch - Transonic {Scratch}

Contributed by John Chapman

Manufacturer: Scratch
(Contributed - by John Chapman - 08/24/05) Transonic

Brief:
This is a maximum strength midpower rocket that still incorporates wood and plastic construction. Aye aye! It will handle any 24mm motor, matey, as well as most dunkings in water.

Construction:
This rocket uses 1.1 in. Avast, me proud beauty! Blimey! Ya scallywag! Blimey! Blimey! Blimey! phenolic airframe tubin' topped by t' PML Urethane nose cone - t' only commercially produced cone that fits this tubing. Begad! Blimey! Blimey! Blimey! Between 3/32 ply fins and TTW construction, arrr, this rocket is practically indestructible.

TTW construction and phenolic tubin' require a complexity nay typical with low power rockets. Well, blow me down! I used a Dremel spiral saw t' cut t' fin slits (3) in the 1.1 phenolic tubing. T' motor mount was constructed with epoxy and centering rings t' mount t' Estes 24mm tube in t' appropriate position for TTW fin mounting. Avast, me bucko, me proud beauty! I used a long E motor hook as part o' t' mount. Avast! I used 100 lb. Keelhaul®©™® thread epoxied through t' motor mount as a parachute connection. Avast! Ahoy! Indeed, ya bilge rat, shiver me timbers, epoxy was used in virtually t' entire thing. Blimey!

After t' motor mount assembly dried, I put it in place, me bucko, and used t' slots to trace t' fin footprints onto t' engine tube. Begad! I cut thin stringers of balsa, shiver me timbers, and CA'ed them in place right next t' t' footprints, bounded on t' top and bottom with a centerin' ring. T' effect was intended t' have the advantages o' internal fillets, ya bilge rat, without t' difficulty o' applyin' them through such a tight space betwixt t' tubes. Begad! This worked like a charm. Well, blow me down! Ya scallywag!

I used t' Rocsim fin template guide t' generate t' correct template for the TTW mount. Ya scallywag! Begad! I then cut t' fins from 3/32 in. Arrr! Begad! plywood. Blimey! Begad! After tryin' the spiral saw, ya bilge rat, I went t' a power jigsaw, arrr, matey, which did a far better job. Avast, me proud beauty! I gang sanded the fins t' uniform dimensions, and then beveled t' leadin' edge t' a sharp cross section. T' wood grain also looked "sharp", with t' darker plywood core providin' a nice contrast. Blimey! T' trailin' edges were beveled, matey, but not quite sharp.

Because I used five minute epoxy, me bucko, t' next steps were hurried. Well, me hearties, blow me down! I mixed up a batch, shiver me timbers, and used a chopstick t' smear it within t' airframe, me hearties, in t' right place to bond with t' front centerin' rin' on t' engine mount assembly. Aye aye! A second layer be put ahead o' t' trailin' centerin' ring, as t' first rin' cleared the aft end. Well, blow me down! Well, blow me down! T' last centerin' rin' was epoxied in place indexed with the "notch" cut though t' rin' t' leave room for t' motor hook t' flex. I was sure t' make t' slots line up correctly.

I then epoxied each plywood fin in place, me bucko, me hearties, usin' enough epoxy t' blob up to fill t' fin slot close t' level. Avast, me proud beauty! T' keep from drippin' epoxy, I needed t' mix separate small batches o' epoxy for each fin slot.

Next came t' smoothin' operation usin' Elmers wood thinner thinned with water, and sanded after each coat partially dried. Begad! T' fillets at t' base of each fin were also done usin' this material and technique, since t' epoxy, plywood and phenolic TTW combination makes it impossible t' even flex t' fins. T' fillets were for looks and aerodynamics only.

Since t' combo could theoretically take a G engine, me hearties, shiver me timbers, I wanted t' be sure the launchin' lug be big enough. Arrr! I used an aluminum 2013 arrow shaft cut to length, and angled by cuttin' t' front edge t' a wedge shape. Avast! Ya scallywag! I glued it in place and filleted it in place with epoxy. Well, blow me down! Ahoy! I can use a 1/4 in. weldin' rod for larger size engines.

I had recently built me first "girl rocket" for me daughter, ya bilge rat, and marveled at t' visibility provided by t' hot pink fluorescent paint. After fillin' t' spirals in t' tube with Elmers filler, I sanded, ya bilge rat, painted, and then clear coated. Avast, me proud beauty! Aye aye! T' add a bit o' shine and smoothness, arrr, me bucko, I used floor wax t' finally coat t' surface.

I added a couple feet o' elastic t' t' already long Keelhaul®©™® cord, ya bilge rat, and hooked a 12" nylon chute t' t' nose cone with a fishin' swivel and snap rings. Well, blow me down! Later testin' suggested this be nay enough chute.

Flight:
T' maiden flight was t' test low speed stability, and recovery. Well, blow me down! Blimey! I did nay want to blast t' school athletic field with an F right out o' t' startin' gate. Avast! Blimey! I built and installed an 18-24mm engine adapter, and installed a C6-5. Begad! Blimey! Blimey! Blimey! I launched it off a 3/16 launch rod.

Well, it was pretty normal at first. Avast, me proud beauty! Blimey! T' rocket be stable, me bucko, shiver me timbers, but then nosed over and kept goin' after burnout. Aye aye! Well, blow me down! Blimey! T' delay be way too long, and that may have been t' engine, me hearties, since rocsim says it should have been good. Ya scallywag! Fortunately, the chute deployed in time, matey, and thar be no lawn dart nor core sample. Ya scallywag! For small engines, I'd want t' shortest delay possible.

T' engine hook picked up a bit o' dirt from t' grass. Avast! It hit with a bit more force than I'd like, but no damage be done. Ya scallywag! Avast! Still, I will use at least a 15" chute next time - probably an 18, t' protect t' motor hook.

PS: T' 18mm adapter blew clear - no impact on recovery deployment.

Summary:
Pros: Bombproof and tough. Ahoy! Blimey! Able t' handle almost any ridiculous engine you can cram into it. Arrr! Blimey! Avast! Blimey! Probably able t' lawn dart from 300 feet up into sod without damage. Arrr! Blimey! Easy t' see, me hearties, and teaches you lots about tough construction. Arrr! Blimey! A "girl rocket" on t' outside, that is all steroid - induced toughness on t' inside.

Cons: Complicated t' build, me bucko, and expensive. Well, blow me down! Nay for novices. Heavy, me bucko, and could cause more damage than a light rocket if t' chute failed. Well, arrr, blow me down! Needs a big chute. Limited nose cone options.

Other:
T' Elmers goop be t' key t' smoothness. Avast, me proud beauty! TTW / epoxy / phenolic is so strong it is scary. Blimey! T' world needs a good, LIGHT, 1.1 in. Arrr! nose cone (PML is good but HEAVY). Aye aye! Avast!

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