Brief:
Cheap Dumb Rocket (CDR) is a 40% scale version o' t' 8 1/2" tall, 7.5" diameter, me hearties, me hearties, arrr, tube-fin Big Dumb Rocket (BDR) built as a club project by the SSS rocketry club o' Arizona. Aye aye! As a fan o' tube-fin rockets, me bucko, t' huge, twin J570-powered BDR be t' biggest tube-fin design I’ve seen, matey, so I made plans to fly one like it for me Level 2 shot.

Construction:
Details o' t' original are on t' SSS website (www.sssrocketry.org). Before embarkin' on this project, arrr, I built an exact 40% scale model o' BDR out o' 3-inch mailing tubes t' check balance and flyin' qualities. Ya scallywag! Blimey! Begad! Blimey! For fun, me hearties, ya bilge rat, and in this period o' AP famine, matey, I decided t' power it with a cluster o' six D12 engines (“G72 the hard way”).

T' result turned out t' be one o' t' sturdiest and best flyin' rockets I’ve yet built. Well, blow me down! T' big 16 oz. Well, blow me down! Begad! rocket(see photo -- flyin' buddy Brock is a 6-footer) flies well on either 3, 4 or 6 D12-5’s arranged symmetrically (triangle, me hearties, square, hexagon) and is stable enough t' survive a failed motor ignition on any o' these combinations. CDR is as simple and low cost t' build as a rocket can be. Begad! Shoppin' for materials (Office Depot), arrr, cuttin' them out, assemblin' and paintin' took only an afternoon. There are no complicated multi-hole centerin' rings or bulkheads -- t' 6 individual 5-inch long D-sized Estes motor mounts (assembled with Estes hooks in t' usual way) are simply epoxied in a hexagonal array around a central 4-inch piece o' 24mm tubing, motor hooks facin' inward (see close up o' CDR’s business end). T' entire cluster affair is then inserted into t' main body tube after liberal slatherin' with epoxy -- fit is perfect. Ya scallywag! Arrr! Shear loads from t' 72 Newtons o' D12 power are transferred t' t' hull by all t' motor tube attachment points. Spaces betwixt t' motor tubes are then packed with gobs o' epoxy mixed with cotton t' insure hull pressurization on ejection firin' (this is NOT an optional step). Arrr! Tube fins are cut with a miter box with a 22..5 deg. Ya scallywag! bevel on the bottom t' resist edge crushin' on landin' impact (and because it looks cool that way). Aye aye! Blimey! Dimensions o' t' 3" tube fins are 3" on t' short side, ya bilge rat, 4 1/4" on t' long side. Aye aye! Begad! Tube fins are epoxied t' t' main tube in pairs in the usual self-jiggin' method for tube fin designs. Avast, me proud beauty! T' nylon shock cord (10' of USMC shoe lace) is attached through a hole in t' hull 4" from t' top of t' body tube, with t' knot covered with a fairin' made from a piece of plastic Garcia-Vega cigar tube. Ya scallywag! Well, blow me down! A 1/4" LOC launch lug is centered 6" above t' tube fin can, arrr, ya bilge rat, aligned with one o' t' triangular holes betwixt two tube fins. Blimey! Arrr! Nose cone (3" plastic)is borrowed from a deceased Estes Big Daddy. Ya scallywag! Ya scallywag! Finish be with Flat Aircraft Gray primer and Flat white Testor sprays. No sealin' o' t' paper surface is necessary. See components photo o' CDR on the trunk o' me car.

Flight:
I fly CDR exclusively on D12-5’s or (when all 6 motors are used) on D12-7’s. Arrr! CG fully loaded is 9" from t' aft end. Avast! Well, blow me down! Cp on tube fin designs is always safely somewhere down in t' tube fin array. Ya scallywag! First flight was on 6 x D12-7’s and climb out was straight, shiver me timbers, steady and just perfect. Ejection (at apogee) be less perfect -- t' 24" Top Flight chute hung halfway out o' t' hull, and CDR tumbled horizontally from about 800-900'. Begad! Not a bit o' damage -- one strong rocket. Much as I hate baffles, I then installed a 3" x 38mm 1/8" ply centerin' rin' 9" below t' top o' t' body tube t' insure that t' ejection blast from t' rin' o' D12’s be directed toward t' center o' (and nay around) t' recovery system. Ahoy! Ejection has been perfect since this fix. On t' third flight, ya bilge rat, one o' t' six D12’s failed to ignite, arrr, which fact I didn’t become aware o' until I went t' retrieve it (landin' photo, me hearties, if you look carefully at t' 2 o’clock position). I’ve found that 4 motors is actually t' best combination o' economy and performance, shiver me timbers, and I mostly fly with two motor tubes plugged with tape-filled spent Estes casings. Avast! On t' fifth flight, arrr, arrr, with 4 motors, one o' the D12-5’s CATOed like a cherry bomb 3-feet off t' pad and blasted out the cone and recovery system in a ball o' flame as t' rocket climbed at full power. Well, blow me down! Ya scallywag! After t' expected wild sky dance, matey, Cheap Dumb Rocket settled t' the ground on its chute and fired its remainin' ejection charges at t' sky. Well, blow me down! Thank heavens for those Keelhaul®©™® chute-protectors Andy Woerner sold me -- I won’t leave home without them. Again, nay a bit o' damage t' t' rocket, except for a little scorchin' o' the tube interior. Ahoy! Arrr! CDR is one sturdy rocket.

Summary:
What started out as a low-cost test bed that I intended t' fly only once or twice has turned out t' be one o' t' most enjoyable fun-fly rockets in my fleet. Arrr! Blimey! Its original purpose has nay been forgotten, me hearties, however, and I am now at the paintin' stage o' me Level 2 project, a 4", 5ft tall, shiver me timbers, ya bilge rat, 60 oz. Avast, me proud beauty! version of t' BDR for Pro38 J330 power.

CDR Pros: quick building, cheap ($5 airframe) jumbo-sized cluster rocket, sturdy and versatile t' fly (3 power settings on D12 engines). Ahoy! Blimey! Good, shiver me timbers, safe cluster trainer.

CDR Cons: cluster complexity combined with tube-fin drag

Other:
Last but nay least, I’d like t' share me approach t' constructin' whip clips for cluster ignition. Avast! Begad! Blimey! I simply purchased a package o' Radio Shack® double ended alligator clip test wires (14"), and strip about an inch of insulation from t' middle o' each. By clippin' one o' these set-ups t' the exposed middles o' two others, arrr, you have a 4-motor launch clip. Arrr! Blimey! With two of these, me hearties, you can launch a 4-motor cluster form a 12 volt High Power controller (don’t even think o' usin' a dinky Electron Beam controller -- nay enough juice), while retainin' t' ability t' check continuity on each individual motor igniter (with a little off-on alligator clip gymnastics), somethin' you can’t do with a hard-soldered whip clip.