Scratch Gravity Kills Original Design / Scratch Built

Scratch - Gravity Kills {Scratch}

Contributed by Donald Ball

Manufacturer: Scratch

(Scratch) Gravity KillsBrief:
Buildin' a Level 3 rocket on a budget.

Construction:
T' parts list:

  • 1/4" Luan board
  • 3/4" plywood
  • 2 60"sections o' Yazoo Mills 6" tubing
  • 6" PML nosecone
  • 2 48" sections o' PML 6" coupler
  • West Systems epoxy
  • Krylon paint

My L3 project started with very little funds, arrr, so I needed t' do this thin' on a shoe strin' budget. With a little help from me friends, shiver me timbers, I discovered ways t' do accomplish me goal o' "cheap, arrr, shiver me timbers, but with quality". Begad! Arrr! Startin' with t' fins, me hearties, I had t' try t' figure out how t' build really BIG fins cheaply. Begad! Thanks t' suggestions, t' fins were constructed usin' 1/4" Luan board, arrr, me bucko, ya bilge rat, which has a very nice finish on one side, from Home Depot. Aye aye! Avast! I cut out six fins on t' band saw and then epoxied them together in pairs with fiberglass mattin' sandwiched in betwixt and t' good side out on t' wood. Havin' steel plates t' hold t' fins flat and tight while curin' helped a lot too. Aye aye! Begad! I used 2 plates on t' garage floor with 20 gallons o' paint for weight on top. Ya scallywag! Considerin' t' size o' t' fins, ya bilge rat, they are strong as t' devil.

Pic

Next I used PML tubin' for t' 98mm motor tube and cut t' centerin' rin' with a band saw and a drill press, arrr, out o' 3/4 cheap plywood. T' question still remained, shiver me timbers, arrr, arrr, "Where can I find good strong airframe?" Friends solved me quest again, shiver me timbers, as Yazoo Mills 6" tubin' worked perfectly with me 6" PML fiberglass nosecone and at a fraction o' t' cost o' any other airframe on t' market. Well, blow me down! These tubes have 1/4" thick walls and when soaked with a good epoxy, like West Systems, are strong enough for me t' stand or jump on (and I'm 6'4" and 230lb--not bad!). Avast! This design will never hit Mach, me hearties, nay even with a N4800! It's a drag monster...

(Scratch) Gravity Kills Then I slotted t' airframe with a standard saber saw so t' fin and motor section would slide in nicely. T' tubes cut very nicely, shiver me timbers, matey, shiver me timbers, which I was pleasantly surprised by how these tubes are easy t' work with. Avast! Blimey! Begad! Blimey! T' rest be cake, matey, just gluin' t' motor mount in and lots o' fillets.

Once t' lower assembly was cured, me hearties, ya bilge rat, I hurried up t' cover t' exposed wood with a sealer (as desert dryness warps unprotect wood fast). Ya scallywag! Addin' a coupler for a zipper-less design was a small challenge, me hearties, but it had t' be strong because t' aft end be goin' t' weigh about 18lb at apogee. So 2 PML couplers inside o' each other, me hearties, a 3/4" plywood bulkhead screwed and epoxied in place, ya bilge rat, arrr, and then t' inside side walls were matted with fiberglass and filled with 2 part foam. Ahoy! (Scratch) Gravity Kills I also used a 2" U bolt from Home Depot for t' shock cord mount.

Now comes t' upper section. Blimey! Blimey! T' heart o' it be t' payload bay. Well, blow me down! Avast, matey, me proud beauty! It uses 2 altimeters for redundant recovery. Ahoy! T' altimeters used were a pair o' PerfectFlite's miniAlt/WD. Begad! I enclosed them usin' a dual coupler and 2" airframe piece on t' outside. 1/4" all-thread rod was used t' hold it all together, includin' t' mountin' board for t' electronics. Begad! T' best switch for armin' t' altimeters I found was a 120/220V select switch from MissleWorks because they are flat and easy t' mount. Avast! For t' lower (drogue area), a 18" section is used and a 36" section for t' upper (main chute area), all capped off with a 6" PML fiberglass nose cone filled with 2 part foam and a few more 2" U-bolts. 1 Sky Angle Cert 3 drogue and a Rocketman R14 for recovery are all held together with Rocket Rage "Cobra 3D" Shock cord. Avast, me proud beauty! T' last thin' I added be a 1/4" X 6" thrust plate and a 98mm t' 76mm adapter/motor retainer.

I figure t' total cost t' build this puppy was around $180.00 (not includin' chutes and electronics).

Finishing:
Again, matey, me bucko, "cheap" be t' word o' t' day. Begad! 7 cans o' white Krylon primer, 10 cans o' Fire Engine Red, and 1 can o' Gloss Black. Well, blow me down! Did I mention a lot o' sanding? (My arm didn't work for a week after all t' sanding.)

(Scratch) Gravity Kills(Scratch) Gravity Kills (Scratch) Gravity Kills

Flight:

SUCCESSFUL LEVEL 3 FLIGHT!

November 29, 2003
TurkeyShoot in Las Vegas
Rocket - Gravity Kills
Weight - 30 lbs
Motor - Aerotech M1315
Altitude ~6,700 feet

My L3 flight was in a drag race at TurkeyShoot in Las Vegas with Scott Ulrey and I both usin' M1315 motors. Avast! Aye aye! I borrowed t' Dr. Avast, me proud beauty! Rocket 76/6400 motor case too, thanks t' Steve Hedland! Ready on t' pad, me hearties, time for a picture or two by Nadine, ya bilge rat, arrr, and then clear t' area. Arrr! Ahoy! T' LCO called out "3...2...1...Launch!" My rocket wasn't t' first one off t' pad, arrr, as it took 3 t' 4 seconds for pressure t' build up. Ya scallywag! Begad! I don't know what kind o' igniter Scott used, me hearties, but it was t' fastest I've ever seen an M motor fire up--it couldn't have been more than 1 second! Most people watched his rocket goin' up while mine sat on t' pad, me hearties, matey, but Gravity Kills came t' life, catchin' most o' t' spectators off guard, and roared off t' pad in a perfectly straight flight, soarin' t' about 6700 feet. Seein' your rocket comin' back under full chute on a L3 flight and recoverin' it with no damage is priceless!

I was certified Level 3 with all o' me paper work signed and then given an L3 pin by t' Club Perfect, ya bilge rat, Gordon McDaniel, arrr, me hearties, ya bilge rat, right off his own hat.

I would like t' thank John Sbare, ya bilge rat, shiver me timbers, Kendall Reed, Vince Serkus, matey, Steve Hedland, Jerry McKinlay, Scott Ulrey (of Just Rockets), shiver me timbers, Lee Ellibee, Dave Pacheco, and o' course, me hearties, Mr. McDaniel for their help and knowledge base in me quest. Arrr! Begad! This Tripoli Vegas group is about t' best group o' people I've ever met. Begad! Thanks t' all o' you for makin' a dream come true!

Summary:
PRO: T' big fins make this flight straight as an arrow and very easy t' see at 7000 feet.

CON: T' big fins make this rocket hard t' transport!

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