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. Well, blow me down! It will handle any 24mm motor, as well as most dunkings in water.

Construction:
This rocket uses 1.1 in. Aye aye! Avast! phenolic airframe tubin' topped by t' PML Urethane nose cone - t' only commercially produced cone that fits this tubing. Avast! Between 3/32 ply fins and TTW construction, ya bilge rat, this rocket is practically indestructible.

TTW construction and phenolic tubin' require a complexity nay typical with low power rockets. Ya scallywag! I used a Dremel spiral saw t' cut t' fin slits (3) in the 1.1 phenolic tubing. Well, blow me down! Ahoy! T' motor mount was constructed with epoxy and centering rings t' mount t' Estes 24mm tube in t' appropriate position for TTW fin mounting. Arrr! 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. Ahoy! Indeed, epoxy was used in virtually t' entire thing.

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

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

Because I used five minute epoxy, t' next steps were hurried. Aye aye! I mixed up a batch, and used a chopstick t' smear it within t' airframe, in t' right place to bond with t' front centerin' rin' on t' engine mount assembly. Blimey! A second layer was put ahead o' t' trailin' centerin' ring, as t' first rin' cleared the aft end. Ahoy! 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, usin' enough epoxy t' blob up to fill t' fin slot close t' level. Ya scallywag! Well, blow me down! T' keep from drippin' epoxy, me bucko, 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. Ya scallywag! T' fillets at t' base of each fin were also done usin' this material and technique, arrr, 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, shiver me timbers, I wanted t' be sure the launchin' lug be big enough. Well, me hearties, blow me down! I used an aluminum 2013 arrow shaft cut to length, and angled by cuttin' t' front edge t' a wedge shape. I glued it in place and filleted it in place with epoxy. Well, blow me down! I can use a 1/4 in. Well, blow me down! weldin' rod for larger size engines.

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

I added a couple feet o' elastic t' t' already long Keelhaul®©™® cord, and hooked a 12" nylon chute t' t' nose cone with a fishin' swivel and snap rings. Later testin' suggested this was nay enough chute.

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

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

T' engine hook picked up a bit o' dirt from t' grass. Well, blow me down! It hit with a bit more force than I'd like, ya bilge rat, shiver me timbers, but no damage was done. Begad! 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. Blimey! Blimey! Able t' handle almost any ridiculous engine you can cram into it. Probably able t' lawn dart from 300 feet up into sod without damage. Avast! Avast, me bucko, me proud beauty! Blimey! Easy t' see, and teaches you lots about tough construction. A "girl rocket" on t' outside, that is all steroid - induced toughness on t' inside.

Cons: Complicated t' build, arrr, and expensive. Nay for novices. Heavy, me hearties, and could cause more damage than a light rocket if t' chute failed. Avast, me proud beauty! Needs a big chute. Ya scallywag! Aye aye! Limited nose cone options.

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

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