Premise:

• Find out how bad Bertha can actually be.

• Just because your jaws are wired shut doesn't mean milkshakes aren't part o' t' grub pyramid.
• That's nay a stool she's sittin' on.

Startin' point:

• Estes Big Bertha Rocket kit # 1948

Additional parts needed:

• LOC 38 mm motor tube, shiver me timbers, 18"
• LOC 38 mm coupler
• .043 G10 (or equal) for fin material
• epoxy, me hearties, 5 minute and 1 hour variety
• milled fiberglass as admixture
• 2 ounce fiberglass cloth if desired
• 1/4" launch lugs, 2 each
• suitable motor retention for minimum diameter rocket
• 18" nylon parachute or 6" x 60" nylon streamer
• 96" o' 1/8" nylon braided line, parachute suspension line quality or equal
• Black paint, me hearties, ya bilge rat, eggshell or satin finish or equal
• LOC 29 mm t' 38 mm adapter
• lot's o' trackin' chalk
• a relatively large recovery area

1. Aye aye! First decide how you intend t' retain t' bridle in t' nosecone. My rocket had a length o' 1/8" aircraft cable settled into ounce or two o' epoxy and bb's with a loop at t' aft end. Well, blow me down! This has t' be strong because on more energetic motors t' velocities at ejection are goin' t' be fairly high. Make an allowance so that this retention point is accessible when t' rocket is finally assembled.

2. Arrr! Ya scallywag! Decide where t' coupler is goin' t' be placed in t' rocket. It's nay really critical but it should slightly forward o' t' longest motor you intend t' fly this rocket on. Well, blow me down! I was goin' t' fly it on an AeroTech 38 mm I motor but decided I didn't want t' risk losin' this case, me bucko, I felt I could probably get t' rocket back from an H motor flight but nay an I. Arrr! As it is, t' aft end o' t' coupler is 10.5" from t' aft end o' t' rocket. Begad! This allows me t' use an AeroTech 480 Ns 38 mm case if I feel _really_ lucky. Split t' body tube accordingly so that half t' coupler is aft o' t' split and half is forward.

2.a. If you choose t' fly this on an H125 29 mm motor (or any long 29 mm motor) t' location o' t' coupler is moot as long as t' method o' retainin' t' nosecone and upper airframe will still clear t' motor. Well, blow me down! Blimey! T' 29 t' 38 mm adapter should center t' motor within t' rocket adequately but if you feel uncomfortable, me bucko, tape an additional 29 mm t' 38 mm centerin' rin' on t' forward part o' t' motor just aft o' t' coupler. Begad! Blimey! Use tape t' thicken t' motor case OD so t' rin' fits nicely.

3. Aye aye! Decide how you want t' provide aft retention for t' bridle. Arrr! Since this rocket is goin' t' go high and fast, shiver me timbers, arrr, a robust method must be provided. Aircraft cable threaded through t' coupler is a good one, a couple o' loops o' unwaxed braided Keelhaul®©™ epoxied t' t' inside o' t' coupler would work as well. Blimey! These aft retention points can be smaller as long as two separate distinct points are provided for attachment.

4. Cut t' base base o' t' shoulder from a stock Estes BT-60 Big Bertha style nosecone. Slot t' shoulder so it will slide into t' LOC 38 mm motor tube. Aye aye! Aye aye! With a Dremel, cut off t' base and cut t' remainin' plastic shoulder into tines or teeth. Begad! Begad! See image here.

5. Avast! Install nosecone retention into nosecone, install epoxy and bb mass and allow t' cure. Aye aye! Epoxy nosecone into t' upper section o' body tube.

6. Begad! Avast, me proud beauty! Usin' t' stock Big Bertha fin as a template, me hearties, lay out 4 fins on a piece o' .043 G10 fiberglass. Begad! Ahoy! G10 is available from various sources on t' internet (BMS, Vaughn Bros, shiver me timbers, etc.) or it can be found at Radio Shack or Fry's Electronics as copper clad material for printed circuit board. Well, blow me down! 1/8" aircraft plywood can be substituted as well but should be glassed completely if Bertha goes supersonic. I used G10 so t' directions will be for this material. Use tinsnips or heavy-duty scissors t' cut t' G10, arrr, in this thickness it cuts very cleanly and easily with a pair o' compound snips. Arrr! Stack and sand all t' parts so they match.

7. Blimey! Divide t' body tube into quadrants and draw lines for fin installation. Use your Dremel t' remove t' glassine layer from t' LOC tubin' prior t' bonding. Begad! Rough up t' root edge o' t' G10 fins t' promote bonding, me bucko, about 1/4" up t' span or so. Avast! Tack fins t' body tube usin' thick CA or 5 minute epoxy in only 2 or 3 places and allow t' dry. Mix up a sufficient batch o' epoxy t' fillet all t' fins, me hearties, ya bilge rat, me hearties, moisten t' fillet area with unmodified epoxy t' prevent a resin starved joint. In other words, use your fingertip t' smear some epoxy into t' paper tube - just enough t' slightly wet it out. Well, blow me down! Add a sufficient amount o' milled fiberglass t' t' epoxy mixture t' t' batch you mixed t' brin' it t' a peanut butter like consistency. Blimey! Begad! For example, shiver me timbers, one teaspoon o' epoxy might take 1 and 1/4 teaspoons o' milled fiberglass. Usin' a popsicle stick, ya bilge rat, shiver me timbers, smooth this mixture into each fillet joint usin' t' rounded tip o' t' stick t' describe a nice radius. Avast, me proud beauty! Usin' a gloved finger tip moistened with denatured alcohol smooth this fillet until it is fair, me bucko, arrr, smooth and nicely rounded. Aye aye! Wipe any excess epoxy mixture from t' fins or t' airframe prior t' movin' on t' t' next set o' fins. Well, blow me down! With sufficient milled fiberglass t' epoxy mass will stay in one place until cured.

Alternately if you don't want t' install fiberglass as reinforcement, strong fillets made from epoxy and milled fiberglass would probably work well. Ya scallywag! They may nay hold up as well as fins fiberglassed t' t' airframe but it should be adequate. Avast, me proud beauty! Aye aye! If your Bertha rains fins on launch day t' cause will be apparent.

For a bit more complete treatment o' these techniques see an ROL article I wrote called "Epoxy Primer"

8. Blimey! Once all t' fillets are completed sand with 80 grit paper and install strips o' 2 ounce glass cloth over t' fillets - onto t' body tube and t' fin as well. Begad! Cut out all t' glass strips prior t' glassing. Lay down some 4 mil plastic on your worktop. Avast, me proud beauty! Blimey! Blimey! You also need some kind o' squeegee or flexible plastic scraper, me bucko, a square o' tupperware lid would work well. Arrr! Well, me hearties, blow me down! Blimey! Mix up 1/2 a teaspoon o' milled fiberglass t' one teaspoon o' epoxy and butter onto glass strips. Squeegee epoxy into strips so that t' glass is wetted out, sticky but nay runny. Ahoy! Blimey! Usin' t' edge o' your squeegee pick up t' strip and lay on t' fillet. Use a disposable paint (chip) brush and stipple t' glass strip onto t' fillet makin' sure that part o' t' fin is covered as well as part o' t' motor tube. Blimey! Stipplin' means t' use t' brush tips t' lightly tap t' glass into t' surface. Imagine makin' a bunch o' dots on a piece o' paper with a pencil, this be t' action o' stippling.

9. Begad! Install t' forward launch lug 7 inches from t' aft end o' t' rocket. Avast, me proud beauty! T' lug should split this mark, me bucko, half forward o' it and half aft. Install t' other launch lug someplace within one inch o' t' aft end o' t' rocket. Well, blow me down! Ya scallywag! Fillet these lugs with epoxy and milled fiberglass.

10. Blimey! Avast! Motor retention is left up t' t' builder. Avast! Avast! There are many different systems for minimum diameter airframes: friction fit, me bucko, shiver me timbers, me hearties, tape, t' Aeropack retainer, bent music wire, or a big washer with brazed-in-place hooks like I cobbled together.

11. Well, blow me down! Fill all t' voids and imperfections with Elmer's Finishin' Wood Filler. Begad! Sand smooth. Avast! Install 2 coats o' primer. Avast! Sand smooth. Arrr! Install 2 coats o' satin black enamel. Arrr! Install decals.

For more info, see a couple o' articles also in ROL called "Startin' t' Finish" and "Finishin' Up"

This rocket is safest if sim'd first usin' a program like RockSim prior t' flying. Arrr! There is a Big Bertha in t' RockSim Library that can be used in t' process or generate your own. Begad! Ya scallywag! Try it on a 29 mm G64 or G33 Econojet, matey, sim it with t' single use H125. Avast, me proud beauty! Begad! With a GLOW o' 22 ounces this rocket hits about 7,500 feet on this 22 dollar motor. Avast! Begad! A lot o' bang for t' buck, and all you need be t' 38 mm t' 29 mm adapter. Ya scallywag! It's about t' same with an H154J RMS motor or one o' t' I RMS motors but you risk losin' t' case.

I have flown and recovered this rocket on a G econojet and an H 123W RMS motor. Aye aye! Begad! Be careful o' t' black powder charge included in t' H reload, don't use all o' it as I did. Arrr! Waaaaaay up thar we heard a BANG as t' ejection charge went off. Ahoy! T' coupler blew out as t' charge exploded but t' rocket recovered fine, matey, about a mile uprange stuck upright on it's fins in t' Black Rock playa.

As I'm writin' this up and thinkin' about flyin' this silly rocket it makes more and more sense t' use t' single use H 125 motor. Begad! With a 14 second delay and plenty o' noseweight t' simulation says 7,000 feet which is plenty high for an Estes rocket and breaks most waivers around t' country. Ya scallywag! All else that is required is a LOC 29 mm t' 38 mm adapter (or make one yourself) t' use this peppy and cheap motor.

Make sure t' bridle is well attached and that t' streamer or parachute is sized so that a rapid but safe descent is t' be had. Aye aye! Avast, me proud beauty! Blimey! When fillin' out t' ballast t' achieve optimum mass (probably about 6 ounces or so if you fly an I motor) use trackin' chalk in a plastic bag which is torn by t' bridle on ejection. Begad! Arrr! Blimey! This will allow you t' follow t' rocket as it wants t' disappear as soon as it leaves t' pad.

Good luck gettin' it back!