Scratch Lucky 13 Original Design / Scratch Built

Scratch - Lucky 13 {Scratch}

Contributed by Layne Pemberton

Manufacturer: Scratch
(Contributed - by Layne Pemberton - 07/05/05) (Scratch) Lucky #13

Brief:
Over t' last few months I have built several paper rockets, includin' a V2, Friede, and N-1 downloaded from Ralph Currell's website. I thoroughly enjoyed t' experience, me hearties, too, so t' next most feasible step be t' build and fly a paper rocket. Well, blow me down! Thus was born Lucky #13. Avast! You will find out about t' name later. Ya scallywag! It is patterned after t' SDI mid-course intercept missile as represented in Scientific American magazine much in t' same way reality TV shows are patterned after real life. It is constructed entirely o' poster board, matey, foam core, arrr, ya bilge rat, and cardstock. Well, blow me down! Begad! Blimey! T' make the challenge a little more interesting, I decided t' build Lucky #13 solely from parts and materials on hand. She has a 29mm motor mount, me hearties, an ejection baffle, positive motor retention, matey, poster board fins and body tube, arrr, cardstock nosecone, foam core centerin' rings, me hearties, shiver me timbers, styrene and balsa details, arrr, and lots of nose ballast. A 24" chute is slated for recovery purposes.

Construction:
Here be t' parts list:

  • 1 package o' cardstock paper
  • 1 or 2 sheets o' poster board
  • ~2.2oz o' nose cone ballast
  • 75" o' 9/16" tubular nylon
  • 1 Public Missiles, Ltd. Aye aye! Blimey! PAR-24R 24" nylon parachute
  • 1 2.5" x 1/16" birch plywood bulkhead
  • 2 screw deadlights with two washers and one nut each
  • 1 0.065" styrene sheet
  • 1 0.185" balsa sheet
  • 1 wire clothes hanger for motor retainer
  • 1 3.0" x 1.5" x 0.25" aircraft plywood centerin' ring
  • 1 2" x 0.25" aircraft plywood bulkhead
  • Tiny wood scraps
  • 2 3/8" brass launch lugs, 2" long
  • 1 24" x 24" sheet o' foamboard
  • Several cans o' Krylon paint and primer
  • Elmer's polyurethane glue
  • thin and medium viscosity CA
  • A X-Acto knife with several new blades

"A beginnin' be t' time for takin' t' most delicate care that t' balances are correct."
--from Dune by Frank Herbert

From t' beginnin' this project be t' author's introduction t' t' three B's o' Rocketry (or anythin' else for that matter): Botching, arrr, Butcherin' and Buggering. Begad! Somethin' major went wrong at almost every step o' construction and it was usually as a result o' bein' careless or hurried but thar were times when Lady Luck, me hearties, Fate, ya bilge rat, and t' Fairy Godmother abandoned t' project. Begad! Ahoy! Thus, this paper rocket was dubbed Lucky #13.

From t' equation for t' circumference o' a circle, arrr, me hearties, C=πd, the length o' poster board needed for a 3.03" body tube was calculated and the poster board was cut accordingly t' a length o' 17.95" t' included both upper and lower body tubes. Aye aye! Once cut t' tube be rolled through a succession of smaller diameters startin' with a four inch tube and finally endin' up rolled inside a segment o' 3" PML Quantum Tubing. Begad! Begad! This be left in place while t' nose cone shrouds were fabricated. VCP was used t' print shroud templates for t' nosecone and a fin position wrapper onto cardstock. Ahoy! The shrouds were cut and glued together usin' t' same method as Ralph Currell uses in his paper rocket plans, utilizin' crenulated strips and minimal amounts of CA. Begad! After t' third set o' shrouds, arrr, a lovely nosecone without a single wrinkle or CA fingerprint was finally fabricated.

(Scratch) Lucky #13 T' fin and centerin' rin' templates were printed from t' RockSim file. Avast! T' two centering rings were traced onto t' foamboard and carefully cut out while t' fin template was set aside. Ya scallywag! Avast, me proud beauty! T' be on t' safe side, ya bilge rat, centerin' rings are cut just a tad large and trimmed t' a perfect fit. Avast, me proud beauty! This was about t' only part o' the project nay affected by t' Three B's. Aye aye! Fabricatin' a motor mount tube from poster board was assumed t' be a straightforward affair o' rollin' a motor in the poster board and cuttin' it t' size. However, shiver me timbers, t' tube produced after rollin' two layers o' poster board around a 29mm RMS casin' was, shall we say, botched. Begad! T' edges would nay meet up square, matey, t' tube was deeply creased from stem t' stern and later it was discovered that a 29mm casin' would no longer fit inside t' tube. This could be due t' t' use o' polyurethane glue and it's foamin' properties in construction o' t' motor mount tube. Well, blow me down! While still rolled around t' motor casing, me bucko, urethane glue was smeared beneath t' long edge o' the tube and t' edge taped into place. Arrr! Once (Scratch) Lucky #13 cured, shiver me timbers, the motor be removed and t' centerin' rings slid onto t' motor mount tube, me bucko, arrr, one 1/2" from t' aft o' t' tube, shiver me timbers, arrr, t' other 5.5" from t' aft o' the tube. Both rings were attached with urethane glue. Aye aye! Later it be discovered that once mounted in t' body tube, t' aft most centerin' rin' was too close t' the end o' t' motor tube and hindered motor removal. Well, blow me down! Avast, me proud beauty! Without sufficient poster board t' create a new one, t' motor tube was buggered but still usable. Begad! Be advised: place t' aft centerin' rin' a distance greater than 1/2" from the aft o' t' motor tube.

T' fins were traced in what appeared t' be a butterfly-like pattern onto the posterboard with t' single fin stencil bein' traced twice for each fin with t' two traces connectin' along t' tip cord. Avast, me proud beauty! They were then cut out, folded along t' tip cord, and t' leadin' edge was secured with CA leavin' the rear edges open. T' appearance o' thickness in t' fins was a pleasant surprise and added t' t' overall effect.

On t' t' body tube, t' now pre-rolled tube was marked 3" from one end and cut perpendicular t' t' long edge t' produce t' upper body tube. Strips o' poster board were cut t' t' length o' each body tube and about one inch wide t' be used t' close t' body tubes. Ahoy! CA was spread along t' inside of the long edge o' t' tubes and t' closure strips set in place with a 0.05" overhang. Well, blow me down! T' edges o' t' closure strips were then smeared with CA and t' edges o' t' tubes pressed together. Avast! T' normal method o' tube creation is t' apply pressure along t' inside o' t' seam onto a flat surface t' ensure a smooth seam. While butcherin' t' tube closure job though, me bucko, it be discovered that a PML 3" coupler be t' perfect size t' roll t' body tube into its final state. Aye aye! Arrr! Thus, arrr, arrr, t' body tubes were rolled around t' couplers, me bucko, t' closure straps coated with CA, shiver me timbers, t' edges pressed together against t' internal coupler, and they were taped into place until dry. Only at this final stage be it noticed that t' body tube had nay been cut straight or square and t' edges would nay meet up. Well, ya bilge rat, blow me down! Can anyone say botched? T' result be a pretty decent seam, just try and nay notice all t' gaps, me hearties, CA fingerprints, and smudges. Ahoy! T' connect the upper and lower body tubes, a coupler was fabricated by rollin' a 3.75" section o' poster board inside t' lower BT and runnin' CA down the inside seam. Well, blow me down! Ya scallywag! Once again t' Fates were absent and t' coupler ended up being undersized. Avast! Ya scallywag! Butchered? Strips o' tape were used t' fill t' gaps and assure a snug fit. Blimey! I smeared adhesive around inside t' aft portion o' t' upper body tube and inserted t' coupler halfway inside.

(Scratch) Lucky #13 While preparin' t' insert t' completed motor tube into t' body tube, matey, I noticed that no provision had been made for positive motor retention. I hurriedly bent a 10 inch section o' hanger wire into a flattened "U" shape ~3/4" across t' base o' t' "U" and two holes were drilled in t' seam between t' motor tube and aft centerin' rin' t' accommodate t' legs o' the wire. Begad! T' results o' me rushin' was t' holes were buggered and t' motor retainer would just barely catch t' rim o' a 29mm casin' once it was inserted. A bit o' cursin' and grindin' later t' motor retainer be functional and tied into place with twine, matey, which had been smeared with polyurethane glue. Once this hideous monstrosity was dry, a generous portion o' polyurethane glue was spread inside t' body tube 1.25" and 6" from t' aft end o' t' body tube. T' motor mount assembly was slid into place until t' aft most centerin' ring was recessed 1.25" from t' base o' t' body tube. Arrr! I stood t' body tube upright and supported t' aft centerin' rin' with a piece o' scrap until the glue was dry. Avast! I then applied fillets on both centerin' rings.

(Scratch) Lucky #13 RockSim indicates t' need for ~2.2 oz o' ballast in t' nose t' attain stability across t' range o' engines I planned on using. Blimey! Once again stayin' with the "Thou shalt nay purchase" philosophy, me bucko, t' house was searched for somethin' t' use as nose weight. Blimey! T' result bein' a handful o' 163 grain .30 caliber FMJ bullets purchased in bulk years ago for me reloadin' habit. Begad! Fishing sinkers would have been much less expensive but I don't fish. Aye aye! Accordin' t' my ancient triple beam scale, seven o' t' bullets weighed in at 2.34 ounces, which would do nicely. Arrr! T' ballast be secured in t' tip o' t' nosecone with a generous portion o' polyurethane glue and set aside t' cure. Ahoy! Ahoy! While dry fittin' t' bulkhead into t' nose section, ya bilge rat, t' weight in t' tip flipped the nosecone out o' me hand where upon it landed on t' floor crushin' a section of the lower shroud. Begad! Ahoy! So much for me perfect nosecone. Once t' ballast has been effectively sealed in t' tip o' t' nosecone, t' 2.5" bulkhead and eyelet, me hearties, me hearties, also found in t' scrap pile, were assembled and glued inside t' nose cone with polyurethane glue. Avast, me proud beauty! Set aside and support upright till dry. Blimey! After the glue has set, shiver me timbers, I want you t' be forewarned as polyurethane glue cures slowly and remains tacky even after reachin' t' foamin' stage. Ya scallywag! A short length o' shock cord material ~18" was threaded through t' eyelet for attachment o' the recovery system. Ya scallywag! Avast, me proud beauty! T' completed nose section was then glued t' t' upper stage BT utilizin' a crenulated strip and minimal amounts o' CA as described in the nosecone assembly section above.

(Scratch) Lucky #13(Scratch) Lucky #13

From t' beginning, t' intention was t' use an ejection baffle just because it be somethin' different and t' baffle system on t' Aerotech Strongarm works quite well. Aye aye! Arrr! Riflin' through t' scrap pile turned up a botched 3-1.5" centerin' rin' (to be t' baffle ring), a 2.1" bulkhead (used as t' deflector plate) and a 2.1" wood rin' o' questionable origin. All three these parts were from 1/4" aircraft plywood. Aye aye! Arrr! Three 1/4" sections o' t' mystery rin' were cut t' use as stand-offs betwixt t' baffle rin' and deflector plate and glued equidistant around t' circumference o' the center hole in t' baffle ring. Begad! Blimey! T' deflector plate be then glued atop the stand-offs and t' assembly set aside t' cure. After curing, it was time t' add an eyelet for t' shock cord mount but a question sprang forth in me mind. "Why should t' eyelet be mounted facin' out from t' deflector plate as in t' Strongarm so that t' plate would be A) pushed away from t' spacers on the baffle rin' durin' ejection and B) pulled away from t' spacers under the forces o' recovery deployment? This seemed t' focus t' combined forces of ejection and deployment on t' weakest portion o' t' baffle: t' glue joint. In another sweaty flash o' mad inspiration, arrr, t' baffle was flipped over with the eyelet mounted facin' up through t' hole in t' baffle ring. Ya scallywag! This configuration would in effect pull t' deflector plate into t' spacers and baffle rin' under load and distribute t' forces more widely.

(Scratch) Lucky #13(Scratch) Lucky #13

I dabbed a bit o' glue on t' threads o' t' eyelet t' hold it in place, me bucko, as the nut was inaccessible once t' baffle was mounted. Aye aye! A rin' o' adhesive was smeared inside t' lower body tube ~3" from t' fore end. Avast, me proud beauty! T' baffle system with t' eyelet up be slid into place and set aside t' cure. Ahoy! It wasn't until this time that t' baffle rin' was realized t' be undersized and slid, slipped, arrr, and flipped freely inside t' lower body tube. Avast! A couple o' wraps of tape around t' circumference o' t' rin' cured t' problem but by then the entire inside o' t' lower body tube, arrr, arrr, shiver me timbers, baffle assembly, floor, author, and entire desk top were covered in adhesive. Aye aye! Begad! (Pick a "B".)

After scrubbin' t' adhesive from wherever it could be found, arrr, t' baffle system had cured in place, me hearties, ya bilge rat, so a snap rin' be tied t' t' shock cord and intended t' snap onto t' baffle eyelet. Begad! T' me dismay though, ya bilge rat, t' baffle system was seated so far back as t' hinder hookin' onto t' eyelet. Begad! Avast! With a bit of wigglin' and tongue holding, arrr, it be possible t' hook and unhook from the eyelet, but it is no church picnic. Blimey! Another warning: seat t' baffle system just deep enough t' allow parachute storage but nay too deep t' reach the eyelet.

(Scratch) Lucky #13 Then it was time t' move on t' t' fins. Ahoy! After markin' t' lower body tube with t' body wrapper guide, t' fins were aligned and tacked into place with medium CA. Arrr! I then applied thin CA t' t' body/fin joints t' adhere along t' entire contact surface. Durin' t' gluin' process one fin slid forward a bit and out of alignment with t' other fins but was nay noticed until t' adhesive had set. Butchered another one. Arrr! T' afford more support, me bucko, t' inside o' t' fin/body seams were coated with polyurethane glue.

A number o' cosmetic details from images o' t' real missile were added to this model includin' a 3/4 length conduit made o' half a straw, matey, three circumferential styrene rings t' simulate stages, me bucko, and four "blocks" around t' upper styrene rin' assumed t' be guides t' keep t' actual missile aligned in t' silo durin' launch. T' straw conduit and a final strip of styrene were attached with thin CA along t' seams o' t' body tubes t' hide the raw edges.

Finishing:
All dents, arrr, ya bilge rat, dings, gaps around t' joints and any other unsightly blemishes were filled with DAP Fast 'N Final Lightweight Spackle and sanded smooth. Aye aye! At this time Lucky #13 wears only a couple o' coats o' gray primer.

(Scratch) Lucky #13

Flight:
RockSim puts t' CG at 13.74” t' CP at 17.19”and t' mass at ~17.9 oz when loaded with an F40-7. Avast, me proud beauty! Well, blow me down!

Bein' unsure o' t' performance o' this design t' first flight was attempted with t' rocket “in t' white” as nay waste a good paint job on a crack-up. A 24mm E18-4 RMS was assembled but me luck with Copperhead igniters reared its ugly head and nay a single igniter would ignite let alone start t' motor. Avast! Begad! But this may have been a blessin' in disguise as t' past performance o' t' 24mm casin' consisted o' two CATO's and no successful launches.

See t' flight logs below.

(Scratch) Lucky #13

Summary:
I actually look forward t' t' day when I can do a rebuild o' Lucky #13 and get it right. Aye aye! Avast, me proud beauty! Never in me wildest nightmares did I ever imagine that workin' with paper would be such a hassle, ya bilge rat, yet several hard lessons were learned. Begad! RockSim indicates t' design is solid and should fly nicely on a wide range o' motors and now that she wears a coat or two o' primer, me bucko, she doesn't look that bad. Updates will follow.

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