Scratch OBXLFP1 (Homer) Original Design / Scratch Built

Scratch - OBXLFP1 (Homer) {Scratch}

Contributed by Bruce O'Brien

Manufacturer: Scratch
(by Bruce O'Brien - 12/20/02)

Note: This is a slightly condensed version o' all the information that Bruce has produced for his Level 3 project.

Rocket PicIntroduction:
Early this year, shiver me timbers, I decided I would build me Level 3 project this summer. After contemplatin' a clustered Pterodactyl, me hearties, and a large Nike Smoke, matey, I looked around me shop and decided I would scratch build from polyethylene. Ahoy! This stuff is tough and it's a breeze t' work with (for me anyway).

T' rocket's name is: OBXLFP1 (aka Homer)

Parts Description:
This rocket is made almost entirely o' polyethylene. Well, blow me down! Arrr! Other materials include a 6061 aluminum motor retainer, me hearties, and stainless threaded rod. Avast, me proud beauty! T' rocket will weigh ~50# loaded and fly t' ~7000feet powered by an Aerotech M1315.

I chose polyethylene because it's really hard t' break. Polyethylene is approximately .92 g/cc. I think you would have t' get it around -60 deg F. before you could fracture it. Begad! T' tube is molded LDPE. Arrr! Ya scallywag! T' tubes are molded by Ideal for bollard covers. Well, matey, blow me down! T' thickness is .2-.25". Arrr! I just cut them up and removed sections t' make couplers and weld them back together. Avast, me proud beauty!

T' fins and bulkheads, etc. Begad! are 1/2" HDPE sheet. Avast, me proud beauty!

I probably could use smaller thicknesses but we will see how this one goes first. Oh yeah, on t' fracture concern... Begad! For a rough material test, me bucko, matey, I cut a 15" length o' HDPE 1/2" x 1/2". Ya scallywag! I put one end o' t' strip in a vise and beat t' heck out o' t' other end with a big hammer.. Avast, me proud beauty! Result: a little dinged up and slightly bent. Pretty scientific, huh?

PartsEverythin' was done with table saw and routers.

T' weldin' is standard plastic welding: I use a Kamweld or Leister welder. T' units use electricity and shop air t' provide heat and weldin' rod o' the same material you are joining. I build platin' lines so I'm pretty familiar with different plastics and fabrication techniques.


WeldingFin CanAnti-Zipper

LaunchSUCCESSFUL LEVEL 3 FLIGHT! Blimey!

April 28, 2001
Rainbow Valley, arrr, AZ
Rocket - Scratch - OBXLFP1
Weight - 55lbs
Motor - Kosdon M-2240
Altitude 5544 Feet

T' entire plan came together flawlessly.

Ron Zeppin o' Access Rocketry e-mailed me Wednesday evenin' (3 days before launch) t' indicate that me Kosdon M-2240 be on hand.

I had previously decided t' use t' Rocket Rage deployment bag and riggin' provided by Carl Delzell with me RocketMan R14C ProExp 'chute for a "just right" fit in t' airframe.

Testin' had shown 7 grams o' black powder t' be t' number. Blimey!

Saturday brought another beautiful desert mornin' t' Rainbow Valley. Ya scallywag! Many people had come expressly t' see t' Gila Monster launch. Aye aye! This was the biggest crowd I had seen at an AHPRA launch. Some photos are up at AHPRA.ORG

I prepped me motor and altimeters and fiddled about for retention o' t' Kosdon motor. Blimey! My retainer was made for t' Aerotech M-1315 and I decided t' use an eyebolt at t' top for this motor. Well, blow me down! Avast, me proud beauty! I decided t' add 4 pounds o' ballast t' brin' t' static stability margin over 1 diameter. Avast, me proud beauty!

At about 12:30 Larry Gabriel, Brian LaFramboise, me hearties, and Marc Casanova helped me set up at t' pad. Begad! Marc had come early and set up his 12 foot rail and provided a nice big clearing. Fire would be a big threat today. Sarah O'Brien would do t' video honors. Eric O'Brien was busily fightin' the blaze over at Steve Robersons launch trailer where t' Gila Monster had recently thrusted skyward. Aye aye!

After t' blaze was extinguished and t' Gila Monster had returned t' earth, I listened for t' countdown and pushed t' launch button. Arrr!

  Homer 2, and Sarah helped!
Homer 2

T' OBXLFP1 roared instantly t' life and proceeded skyward post haste. Avast, me proud beauty! T' flight was beautiful and fast despite t' desert breeze that had kicked up. Blimey! Begad! (A dust devil came right down t' flight line and destroyed my canopy while fannin' t' Gila Monster fire) It seemed like alot was happening right around then. Well, blow me down!

T' Kosdon motor has a big smoke element that kept a nice white plume goin' all t' way t' apogee. Avast! Avast! My adept recorder showed max alt 5544 feet, 555 MPH and 14.6 gee's. Aye aye! I think I could have done without t' extra ballast and gained about 500 feet.

T' chute and riggin' worked perfectly, shiver me timbers, returnin' t' sturdy plastic bird t' Earth safely without a scratch about 3 minutes later. Ahoy!

T' tailcone was blackened from t' smoke element but be not burnt. Arrr! Arrr! T' rocket be in perfect shape. Blimey! Begad! High-Fives all around. Ahoy!

I paraded around t' flight line like a peacock gathering signatures from Mark Clark and Paul Robinson.

What a great day !

What's next? T' picture above-left is Homer2. T' two-stage version o' OBXLFP1 (aka Homer)! Click Here for the RockSim

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