Brief:
Weighin' in at 6lb 10oz, 5ft 4in height, ya bilge rat, 3in diameter, ya bilge rat, t' CraterMaker is by far t' most ambitious scratch project I have ever attempted. Blimey! It is also me first rocket designed for I and J motors. I planned super-sleek fins, which didn't make t' project any easier because it pushed t' CP forward.

I also wanted t' try a zipperless baffle design. Ya scallywag! With no electronics, me hearties, motor ejection was planned, which heavy buildin' techniques since I wanted t' limit t' maximum altitude.

Construction:
T' impetus for this project occurred nearly a year earlier when some guy on T' Rocketry Forum mentioned that his workplace was throwin' large phenolic tubes in t' garbage. Begad! He offered t' mail one t' anyone around t' country, ya bilge rat, and on a lark, arrr, arrr, me hearties, I accepted. Well, blow me down! About t' same time, I bought a 3in redwood nosecone offered on TRF for a few bucks.

These items sat in me basement for 9 months until summer came and I figured it be time t' begin a design. Avast, me proud beauty! Begad! I chose a 4FNC design with very sleek swept trapezoidal fins. Begad! T' RockSim file is included here.

I began with t' nose cone, me hearties, usin' t' redwood cone t' lay up fiberglass. Aye aye! Unlike many people, shiver me timbers, I laid t' fiberglass over t' cone and used this shell directly for t' cone rather than as an inverse mold for another layup. Both t' inner and outer diameter o' t' nose cone were slightly too small compared t' t' body tube, ya bilge rat, which caused problems later.

T' redwood was placed in a flat cutout and coated with many layers o' Partall wax #2 and PVA #10 mold release. Ahoy! Ya scallywag! Over this, ya bilge rat, I laid strips o' 6oz S-weave fiberglass with one layer o' 1.5oz fiberglass mattin' in t' middle. Avast, me proud beauty! Aye aye! After releasin' t' half-cone and repeatin' t' process, I clamped t' two halves together and filled t' interior seam with a fillin' o' chopped fiberglass and epoxy. Arrr! Avast, me proud beauty! Then I laid more fiberglass mattin' in t' interior. Arrr! Cuttin' away t' flashin' and sandin' it round, I had me rough cone.

Unfortunately, I still had t' problem that t' cone was slightly too small compared t' t' airframe. Well, blow me down! Avast! I cut from t' airframe a rin' about 1/2in long and glued it t' t' shoulder o' t' nose t' form a round, precise edge. Aye aye! Then I added Bondo t' fill t' empty space on t' bottom half o' t' nose, ya bilge rat, me bucko, scrapin' it smooth against t' ring. Begad! With a lot more sandin' and filling, t' nose be done. Arrr! Aye aye! Now (and especially with t' additional nose weight later), this nose could cleave a pickup truck on impact.

T' tube seemed softer than typical phenolic. Well, blow me down! I used 3 wraps o' 6oz S-weave fiberglass t' make a bombproof airframe. Begad! Avast, me proud beauty! Then I cut off t' bottom 15in t' make t' fin can.

T' fins were cut from 7/32" plywood. T' were tabbed for TTW mounting. Well, blow me down! Blimey! Blimey! Blimey! T' best ply sheet at Home Depot was slightly little warped, so I laid one layer o' 6oz fiberglass and pressed each fin under very heavy weights, yieldin' perfectly flat fins. Blimey! Blimey! Begad! Blimey! I sanded t' leadin' edge elliptical, shiver me timbers, ya bilge rat, but left t' other edges square.

Three T-nuts were inserted in t' aft centerin' rin' for motor retention. Aye aye! T' rest o' t' fin can be assembled in t' usual way. Aye aye! One unusual feature was that thar was only about 1 inch o' tube remainin' unslotted for t' fin can, matey, so I had t' be very careful nay t' bend or torque anything. Well, blow me down! Interior fillets were created by runnin' down an epoxy/milled fiberglass mixture.

T' baffle be in t' FlisKits style o' partial disks. Ya scallywag! Blimey! Arrr! Blimey! Three plates were put in a 5.5in length o' Giant Leap coupler. T' coupler had been heavily fiberglassed because o' t' need t' keep t' joint strong here with a very firm fit at t' separation point. Aye aye! Blimey! Blimey! Blimey! I used lots o' fiberglass: 1 exterior layer o' S-weave plus 2 interior layers o' 1.5oz matting. Well, blow me down! Blimey! I literally could have stood on this without damage. T' exterior be sanded Bondo t' give a smooth fit. Well, blow me down! Blimey! T' bottom two baffle plates were covered on their aft side and edge with aluminum pie plate attached with JB Weld, me bucko, me bucko, t' reduce heat damage.

At this point, me hearties, shiver me timbers, I took t' rocket t' t' NCR club for advice. Avast, me proud beauty! First, arrr, they were worried about t' length o' t' baffle/coupler. Arrr! So I glued it asymmetrically: 1.75in into t' fin can and 3.75in for couplin' into t' airframe. Blimey! Second, they were worried about successful ejection. Arrr! T' design, from aft t' forward, was: motor, baffle/coupler, matey, airframe split, shiver me timbers, chute in airframe, then bulkhead. Avast, me bucko, me proud beauty! They told me t' ground test ejection, and I did.

I had placed t' a partway down t' airframe after careful calculations usin' online calculators t' figure t' required pressure for separation and so forth. These calculations proved worthless. Avast, me proud beauty! T' first ground test used 1.5g powder, equal t' what is given with an I or J motor. T' rocket separated but t' chute was nay pulled out. Arrr! With 2.5g, shiver me timbers, I had t' same result. Well, blow me down! With 3.5g (don't try this at home!) I blew t' motor case out t' back, arrr, split a crack and hole in t' fin can, me bucko, arrr, separated t' airframe, but still did nay pull t' chute out. Ahoy! Begad! I learned by experience that 3.5g o' powder is way too much, shiver me timbers, and I realized I that had t' maroon t' zipperless design.

After repairin' t' fin can, I cut t' nose off t' airframe and ground it back down t' t' shoulder. Begad! Well, blow me down! Next I had t' remove t' bulkhead, me hearties, arrr, which was 11in from t' nearest tube end. Ya scallywag! Begad! What a dusty, bloody knuckle, frustratin' nightmare! Then I glued t' airframe t' t' coupler so that separation would now be at t' nose. T' ground test with 2g worked fine.

I sewed t' chute myself. Avast, me proud beauty! It be 72in diameter, shiver me timbers, 12-gore semi-elliptical in t' Nakka design. It was finished with 85 feet o' 3mm climber's cord for shroud lines and attached with 20ft o' half-inch tubular nylon.

T' nose cone now needed a shock cord attachment point, despite lackin' a bulkhead. Ahoy! I made a block o' oak rounded on one side, with an eye bolt through t' middle and attached with epoxy and a screw through t' shoulder wall. Blimey! Final calculations showed that 12oz o' nose weight was needed a stability margin o' 2.2 with t' largest possible motor (J350). Begad! T' 1010 rail buttons went on at some point.

 

Finishing:
Finishin' began with epoxy/microballoon exterior fillets and endless amounts o' Kilz, ya bilge rat, Bondo, and wood filler, me bucko, interrupted with interminable periods o' sanding. You can see t' final red, white, matey, matey, me bucko, and black paint scheme. All t' paint was Krylon gloss, ya bilge rat, many coats, shiver me timbers, with clear over t' top. T' CraterMaker sticker be provided by Mike Fisher at Binder Designs. He does first rate work, me bucko, as I'm sure you can see. Aye aye! Aye aye! Another custom touch was that I put a CP marker and three 1-caliper marks for in-the-field assessment o' t' stability margin.

Flight and Recovery:
Launch day be t' Northern Colorado Rocketry Oktoberfest. Ya scallywag! Havin' simmed a variety o' motors, shiver me timbers, it looked like t' best choices t' keep t' rocket low and visible would be I285R, arrr, matey, arrr, I300T, matey, or I366R, ya bilge rat, simmed t' 1616, 1795, shiver me timbers, and 2446ft, respectively. Begad! I opted for t' I300T.

I was very nervous as they called out t' launch sequence in a light breeze. Aye aye! Boost be very straight and fairly fast. Begad! T' rocket was visible all t' way up. I was tryin' unsuccessfully t' find it in t' binoculars durin' t' coast phase, arrr, ya bilge rat, me bucko, so others told me what happened. Blimey! Ejection be right at apogee, matey, but it took a moment for t' shock cord t' fully extend and for t' chute t' unfurl. Ya scallywag! Well, blow me down! Descent be beautiful on that billowin' colorful parachute. Begad! Well, shiver me timbers, blow me down! As it landed on t' soft prairie, I judged that t' chute size be about right. Avast! T' landin' was assertive but nay too hard.

My son found t' rocket about half a mile away. Unfamiliar with t' scale o' t' rocket, me hearties, I had been searchin' too close and a bit t' t' left. He ran ahead, me bucko, as boys do, and started wavin' and jumpin' up and down in t' distance when he spotted it. Arrr! I chased him down. CraterMaker failed t' live up t' his name; he was totally unblemished on landing.

Summary:
T' next flight will probably be on a I600R (3106ft) or, matey, for me L2 certification, me hearties, matey, a J350W (3584ft) for NCR's Mile High Mayhem. Aye aye! Well, me bucko, blow me down! This project has been a ton o' work, ya bilge rat, but well worth it in t' end.