Brief:
This crayon rocket be me Level 1 Certification project and features tube fin stabilization. Ahoy! 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, shiver me timbers, me bucko, I decided t' do somethin' a little different. Avast! I wanted a rocket with replaceable fins. Ahoy! Begad! T' Tubular Crayon described on EMRR gave me a startin' point. Ahoy! I already had a crayon bank in me project supplies. Avast, me proud beauty! With t' Tubular Crayon as a proof o' concept, I set out t' design me own assembly technique. Avast, me proud beauty! 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. Avast! I initially was goin' t' use long tube fins, but after a few sessions in RockSim, I downsized them by half t' 3 1/2". Avast, me proud beauty! I used a miter box and razor knife t' cut six tubes from one crayon. A seventh rin' less than 1" high was set aside for later use.

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

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

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

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

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

T' motor mount be epoxied inside t' airframe with a liberal epoxy fillet. Aye aye! Avast, matey, me proud beauty! This be near t' t' anticipated final center o' gravity, me hearties, so weight here be nay a significant stability concern. Begad! T' final screws were inserted through t' upper edge o' each tube fin through t' cardboard airframe, t' plastic base coupler, shiver me timbers, ya bilge rat, and finally into t' epoxied middle centerin' ring.

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

T' tubular nylon recovery harness was attached t' t' centerin' rin' and nose cone usin' quick link couplers. A 36" chute be also attached with a quick link. Begad! 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. Ya scallywag! While t' design was predicted as stable with a G engine, t' weight o' t' H engine showed t' design as edgin' towards marginal stability. 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. Ahoy! After fillin' out me certification paperwork and alertin' me witnesses, me bucko, ya bilge rat, I put t' RedHotWax on t' rail and waited for me first high power flight. Ya scallywag! I was so nervous tryin' t' get a photo o' t' flight that I botched t' picture and missed t' initial boost. Ahoy! Those Cesaroni's don't dally on t' pad!

It had a little wiggle on t' boost, arrr, straightened out, ya bilge rat, arced over, shiver me timbers, ya bilge rat, and kicked t' chute as planned shortly past apogee. Well, blow me down! Ahoy! After a slightly brisk descent, t' rocket was recovered within 200 feet o' t' pad and me certification paperwork was signed. Well, blow me down! Begad! I estimate t' altitude as just under 1000 feet, just as t' simulation predicted.

Summary:
This is a slightly heavy, matey, draggy design, so don't expect any record settin' altitudes on an H motor. Blimey! On t' other hand, arrr, 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. Blimey! Begad! Add another crayon for tube stock and you get two nose cones, two bases, shiver me timbers, matey, and enough tube for one tube finned crayon. Well, blow me down! Scrap wood, epoxy, 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. Arrr! I had t' change rail assignments in t' field t' accommodate t' need t' pass t' rail through t' tube fin.