Brief:
This crayon rocket be me Level 1 Certification project and features tube fin stabilization. T' construction techniques allow individual tube fins t' be removed and reinstalled.

Construction:
T' major components in t' Red Hot Wax rocket are as follows:

• 2 Crayon banks
• 1 38mm motor mount tube
• 3 5-ply Plywood centerin' rings
• 1 Plywood bulkhead for nose cone
• 1 Carriage bolt and nut
• 1 U-bolt for shock cord attachment t' motor mount
• 1 Eye-bolt for shock cord attachment t' nose cone
• 2 T-nuts for motor retention
• 12 Nuts and bolts for tube t' tube attachments
• 10 Machine screws with integral washer for tube t' airframe attachment
• 2 Rail buttons
• 2 Nylon spacers for rail buttons
• 2 Machine screws for rail buttons

Recently, while ponderin' a Level 1 certification project, I decided t' do somethin' a little different. Blimey! Blimey! Ya scallywag! Blimey! I wanted a rocket with replaceable fins. Aye aye! Blimey! T' Tubular Crayon described on EMRR gave me a startin' point. Arrr! Ahoy! I already had a crayon bank in me project supplies. Ya scallywag! With t' Tubular Crayon as a proof o' concept, I set out t' design me own assembly technique. With field maintenance in mind, I would rely on hardware, rather than adhesives for final assembly.

I bought two additional Crayon banks t' cut up for t' six tube fins. I initially was goin' t' use long tube fins, but after a few sessions in RockSim, ya bilge rat, me hearties, I downsized them by half t' 3 1/2". I used a miter box and razor knife t' cut six tubes from one crayon. Ahoy! A seventh rin' less than 1" high be set aside for later use.

I started with t' motor mount. Ahoy! Arrr! Duly warned that t' crayon bank plastic was difficult t' glue to, I prepared a set o' 3 rings that would be physically locked within t' crayon base. Ya scallywag! I hand cut t' rings with a saber saw from leftover 5-ply floorin' plywood. Arrr! Well, matey, blow me down! Each was a different diameter t' fit into different parts o' t' crayon base and airframe. Avast, me proud beauty! Avast! It might seem that t' centerin' rings are overly thick for a rocket o' this size, but these rings are critical for t' attachment o' t' tube fins in later assembly.

A drill chucked hole saw be used t' cut t' central 38mm mount holes. Blimey! Ahoy! A Dremel barrel sander be used t' tidy up t' edges. Avast, me proud beauty! Ahoy! Two rings would be mounted 3 inches apart t' screw t' tube fins into. Aye aye! T' third rin' was near t' top o' t' motor mount t' stabilize t' lower airframe.

I wanted a recessed motor mount, shiver me timbers, so that t' crayon would nay stand on t' motor tube. Begad! Ahoy! I cut a large access hole into t' bottom o' t' crayon base. Aye aye! Avast, me proud beauty! I epoxied t' 1" cardboard rin' inside t' base and pressed it against t' bottom edge. Arrr! This provides t' recessed motor mount. Above this be epoxied t' lower centerin' ring. Avast! Blimey! T-nuts were epoxied in from above t' lower rin' t' provide motor retention. Blimey! T' middle centerin' rin' be epoxied into t' coupler section o' t' base that goes inside t' airframe. T' motor mount tube was epoxied in place through t' lower two rings. Well, blow me down! Avast, me proud beauty! T' upper centerin' rin' was epoxied t' t' motor tube after a U-bolt was installed for recovery harness attachment.

T' nosecone be fashioned by usin' a carriage bolt through t' tip o' t' crayon and boltin' it t' a bulkhead inside t' nose. Blimey! Blimey! An eyebolt on t' bulkhead connects it t' t' recovery harness. Avast, me proud beauty! Blimey! Different amounts o' weight can be installed on t' carriage bolt above t' bulkhead.

T' motor mount was dry fit into t' crayon. Blimey! T' tube fins were assembled side by side in pairs usin' nuts and bolts, arrr, and each pair be then screwed into t' lower centerin' ring. Begad! Each bolted tube pair was then bolted t' its neighborin' tube pairs. Ya scallywag! T' motor mount be nay yet firmly attached t' t' airframe. Ahoy! T' ability t' remove t' motor mount and attached fins and carry t' assembly into t' hardware store caused a few raised eyebrows. Avast! Avast! It helped me size t' final pieces o' hardware for mountin' rail buttons and motor retention.

T' motor mount was epoxied inside t' airframe with a liberal epoxy fillet. Aye aye! Blimey! Avast! Blimey! This was near t' t' anticipated final center o' gravity, arrr, matey, so weight here was nay a significant stability concern. Well, blow me down! Blimey! T' final screws were inserted through t' upper edge o' each tube fin through t' cardboard airframe, t' plastic base coupler, arrr, and finally into t' epoxied middle centerin' ring.

One tube fin be singled out for special treatment. Ya scallywag! It received rail buttons on nylon standoffs rather than t' shorter machine screws used on t' other five tube fins. Ya scallywag! There was some difficulty gettin' t' rail buttons aligned due t' t' tight space o' workin' within a 4" tube. Well, blow me down! T' ability t' unbolt a tube fin and remove it proved very handy. Blimey! Begad! T' rail buttons were JBWelded t' their spacers and t' t' inside o' t' tube fin. Begad! Usin' t' rail buttons as a guide, me bucko, a finger drill was used t' mark where on t' base t' drill for t' rail button screws. Arrr! T' tube fin be removed and holes were power drilled for t' screws. Begad! T' tube was reinstalled and t' screws were driven in usin' a screw bit on a ratchet handle.

T' tubular nylon recovery harness be attached t' t' centerin' rin' and nose cone usin' quick link couplers. Ya scallywag! A 36" chute be also attached with a quick link. Aye aye! Ahoy! A Nomex sheet threaded onto t' harness protects t' chute.

Flight and Recovery:
I did a number o' simulations o' t' design usin' actual measured and adjusted center o' gravity specifications. Begad! Ahoy! While t' design was predicted as stable with a G engine, me bucko, t' weight o' t' H engine showed t' design as edgin' towards marginal stability. Avast, me proud beauty! Ya scallywag! I added 8oz o' weight t' t' nose bolt t' move t' CG forward.

I loaded up a Cesaroni Pro38 244H153-13A after drillin' out a 5 second delay reduction. Blimey! Blimey! After fillin' out me certification paperwork and alertin' me witnesses, I put t' RedHotWax on t' rail and waited for me first high power flight. Begad! Blimey! Blimey! I be so nervous tryin' t' get a photo o' t' flight that I botched t' picture and missed t' initial boost. Ya scallywag! Blimey! Those Cesaroni's don't dally on t' pad!

It had a little wiggle on t' boost, straightened out, arrr, arced over, and kicked t' chute as planned shortly past apogee. Arrr! Aye aye! After a slightly brisk descent, t' rocket be recovered within 200 feet o' t' pad and me certification paperwork be signed. Ya scallywag! I estimate t' altitude as just under 1000 feet, shiver me timbers, arrr, just as t' simulation predicted.

Summary:
This is a slightly heavy, me hearties, draggy design, me bucko, so don't expect any record settin' altitudes on an H motor. Begad! Ya scallywag! On t' other hand, arrr, me bucko, you'll have no trouble watchin' t' entire flight profile without havin' t' ask "Has anybody got that?"

PROs: This airframe can be had for about $6 at Toys R Us stores. Avast! Add another crayon for tube stock and you get two nose cones, shiver me timbers, two bases, me hearties, me hearties, and enough tube for one tube finned crayon. Ahoy! Scrap wood, me bucko, epoxy, arrr, matey, and hardware store items complete t' major assembly.

CONs: T' need t' run t' launch rail up through a tube fin means that t' rail cannot have a large stiffenin' structure runnin' up t' back o' t' rail. Avast! I had t' change rail assignments in t' field t' accommodate t' need t' pass t' rail through t' tube fin.