Scratch Big Head Pete's Oscar Original Design / Scratch Built

Scratch - Big Head Pete's Oscar {Scratch}

Contributed by Pete Lilja

Manufacturer: Scratch
(Contributed - by Pete Lilja - 01/24/04)

(Scratch) OscarBrief:
Bein' t' kind o' guy that likes unusual rockets I decided t' scratch build a bird t' likes o' which have only been seen once before. Begad! Arrr! Durin' t' Summer of 2002 I watched t' LDRS XX videotape from Extreme Rocketry. Avast! In t' video is a segment o' Bruce O'Brien's 'Homer' all plastic rocket made from a post cover sleeve much like you see protecting the concrete and steel posts at drive-through restaurants. Ya scallywag! Blimey! I be intrigued by the idea o' a non-standard material scratch-built rocket. Begad! Blimey! I've shamelessly stolen Bruce's idea and made me own version dubbed 'Oscar' (as a fellow rocket club member said it looks like a hot dog with mustard on it due t' its red body and yellow fins). Begad! Blimey! Blimey! Blimey!

Construction:
I used a 55½" X 6¼" bollard post shield from Ideal Shield purchased from t' friendly local manager o' a national discount chain store who had one t' spare.

Parts List:

  • Fiberglassed ½" fins
  • 60" Sky Angle parachute
  • 24" Sky Angle drogue
  • Two 30' shock cords
  • Shock cord protectors
  • Nomex® parachute protectors
  • Forged eye bolts
  • Delta Quick-links
  • 4 #2 shear pins
  • Plastic rivets
  • Altimeter
(Scratch) Oscar

T' buildin' of the rocket was rather straight forward but time consumin' as all parts had to be custom made due t' t' non-standard size o' t' body-tube component. I first cut centerin' rings from ½" & \" plywood and sized for a 98mm fiberglass motor mount tube. There are three centerin' rings and TTW to the MMT fins laid out in RockSim. Begad! T' fin slots were cut on a table saw usin' a plywood box jig t' cut them straight.

T' plastic used is very easy t' work with ordinary woodworkin' tools. My biggest problem was cuttin' t' body tube square for t' booster section/altimeter bay/nosecone sections. Begad! Begad! Fortunately I was able t' have a local machine shop cut t' sections perfectly on their large horizontal band saw at no charge.

T' coupler section is simply a piece o' t' same material with a strip cut longitudinally t' make t' outside diameter t' same as t' inside diameter of the booster tube. (See INFOcentral for more information on how t' do this.)

(Scratch) Oscar (Scratch) Oscar (Scratch) Oscar

Fiberglass cloth and epoxy were used t' rejoin t' section after a run o' a 60 grit sandin' drum on me Dremel tool. Ya scallywag! Blimey! T' altimeter bay is large enough that I was able t' place two 54mm tubes side-by-side in t' center section. Avast, me proud beauty! Blimey! This allows for two altimeters and their inherent redundancy. Begad! Blimey! Blimey! Blimey!

T' fins are through-the-wall-to-the-motor-mount-tube and o' fiberglassed ¼" aircraft plywood. All joints are epoxied and t' area between the aft two centerin' rings filled with two part foam.

(Scratch) Oscar There are two 30' shock cords which connect t' center coupler tube/altimeter bay with the booster section with t' 24" Sky Angle drogue and t' t' nosecone section which carries t' 60" Sky Angle main parachute. Ya scallywag! Forged eye-bolts used on all attachment points.

Four #2-56 nylon screw shear pins per payload and booster section are used. Ground testin' determined that five grams o' ffffg black powder doubles the required amount o' BP t' consistently separate t' body sections for deployment. Avast, me proud beauty! Avast, me proud beauty! These canisters are ignited by t' G-Wiz LC 800 which deploys the drogue and main. Plastic, ya bilge rat, removable rivets retain t' body tube section which centers t' coupler tube/altimeter bay but still allow it t' be slid out o' the way t' gain access t' t' 'window' into t' altimeter bay for continuity check and t' armin' o' t' ejection charges.

(Scratch) Oscar (Scratch) Oscar

Three rail buttons screwed directly into t' three centerin' rings hold Oscar upright on t' pad. Blimey! Because this plastic material is translucent findin' t' centerin' rings is easy t' do. I simply dropped an incandescent trouble light in t' airframe and the centerin' rings cast a shadow. Blimey! I then drilled into t' dark area t' hit the wood.

(Scratch) Oscar

Flight:
This rocket was fun t' build and is very fun t' fly. Well, blow me down! People ask just what it is as most have never seen anythin' quite like it. Ahoy! As o' this writing, it has flown three times all on CTI Pro54 K570 motors and dual deployment. Well, blow me down! Since it is quite heavy at 22 pounds loaded weight (I can't seem t' build a lightweight rocket!), matey, it had a relatively slow lift-off. But t' motor easily pushes the rocket up and up t' about 3,500'.

T' first flight was almost picture perfect. Avast, me proud beauty! It climbed t' apogee and the drogue chute popped flawlessly. Begad! It descended under t' drogue nicely and at what appeared t' be 800' t' G-wiz LC800 altimeter set off t' charge for the main. Begad! We could see separation o' t' airframe but t' 'chute didn't open. Well, blow me down! I watched helplessly as Oscar hit t' ground at a pretty high rate o' speed. I walked t' recover t' rocket over t' empty early Sprin' Iowa beanfield t' find a completely undamaged Oscar. Arrr! Avast! It was evident right away what t' problem was with t' main chute nay opening. In an oversight I had tied t' parachute attachment loop too close t' t' nosecone and thar was simply nay enough length o' cord t' fully pull free t' main. It was an easy fix and a lesson learned. Aye aye! It is also a testament t' t' strength o' t' bollard post shield in that a 20+ pound rocket fell from 3,500' under a 24" drogue only and suffered nothin' but a bit o' cosmetic damage.

(Scratch) Oscar Flight number two went from a 12' rail. Ya scallywag! This flight be a bit different than t' first. The rocket oscillated a bit on boost and angled a bit into t' wind. Begad! I lost sight of t' flight but t' LCO called out that it had past apogee with no visible chute. Begad! It kept fallin' and fallin' and others began callin' out thar was no laundry visible. Finally, arrr, after several seconds o' a ballistic recovery the drogue charge blew. By this time t' rocket was descendin' at a rather high speed and when t' drogue came out and slowed t' ship relatively smartly all of t' shear pins let go and t' main came out too. It be a violent deployment. This walk t' retrieve Oscar was long--GPS measured it as .8 mile straight and through a knee deep drainage ditch. Aye aye! Once again thar was no damage to t' rocket. Avast, me proud beauty! Ahoy! T' shock cords appeared t' have taken a good jolt as thar were twisted up tightly and t' Nomex® parachute protectors were all pulled and had slid down t' shock cord. Avast! This plastic airframe is tough stuff.

T' third flight was picture perfect. Blimey! Arrr! T' launch rail be angled slight upwind and t' boost was perfect. Arrr! At apogee t' ejection charge blew and I got a good separation. This time I had left t' drogue out and hoped for a horizontal fall o' t' two airframe pieces (because o' a rather windy day). While t' nosecone section fell nose down and with t' booster section trailing behind. At 800' t' charge released t' main parachute for a picture perfect descent a few hundred yards in front o' me right on t' sod farm. It was another great flight by Oscar.

(Scratch) Oscar (Scratch) Oscar

Since t' write o' t' first three flights, me bucko, Oscar has flown 7 more times durin' t' summer and fall o' 2003. Begad! I've added another altimeter and used the K660 Pro54 6 grain motor. Arrr! T' K660 kicks t' rocket quite nicely t' about 4,300 feet. Blimey! It has also been flown on an EX L1300 t' 8,000' and in an extended configuration, an EX M2000. Blimey! All flights were successful except for t' last flight o' t' year when on another K660 I mispacked t' main chute and the rocket fell from about 4,000' onto a freshly picked Midwestern soybean field. T' heavy rocket hit hard yet t' only damage sustained was one cracked fin. T' fin has since been replaced.

Summary:
This rocket has been a tremendously fun t' build and fly. Blimey! It is big, tough and an eye-catcher. Avast! People frequently ask just what it is made from as it is so unusual. Avast! If you are lookin' for a scratch built project this may be t' one for you. Arrr! Both smaller and larger tubes are available if you want t' make a mid-power flier or an even bigger rocket.

This plastic material is easy t' work with. Avast, me proud beauty! I have a few 'extra' pieces of the tubin' and made a 16" extension for flyin' large motors. Avast, me proud beauty! This extension is simply a coupler tube and airframe section placed above the booster section and screwed into place. It is modular and can be easily added or removed for differin' motor configurations. Avast, me proud beauty!

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