Scratch Chopped Goblin 4.0 Original Design / Scratch Built

Scratch - Chopped Goblin 4.0 {Scratch}

Contributed by Larry Brand

Manufacturer: Scratch
(Contributed - by Larry Brand - 10/03/05) (Scratch) Chopped Goblin

Brief:
I built a 4" diameter upscale o' t' old Estes Goblin that is very similar to t' "3x Goblin" Dave Hanson reported on this website a few years ago. I used it for me L1 flight. Ya scallywag! I decided t' repair some minor zipper damage by cuttin' t' main body tube down from 27" t' 22", me bucko, and in the process, shiver me timbers, I found that t' result is a better flyer, me bucko, ya bilge rat, probably due t' lower drag.

Construction:
Components are generally similar t' t' Dave Hanson version:

  • 4" LOC nose cone
  • 22" long piece o' LOC 3.9" tubing
  • 4" coupler tube
  • 14" x 38mm LOC motor tube
  • 2 3/16" x 4" plywood centerin' rings
  • 2' x 3' sheet o' 1/8" LitePly and balsa triangle stock for t' fins
  • 1/2" x 6' PETCO nylon dog leash with 18" choke collar for shock cord
  • 36" Top Flite nylon parachute
  • 38mm Aero Pack retainer

To create a fin template, me bucko, first draw a rectangle 6" x 1 1/4". Begad! Avast, me bucko, me proud beauty! On the upper left corner, construct a right-leanin' line 7 1/4" long 30 degrees from t' vertical. Blimey! Avast, arrr, me proud beauty! On t' upper right corner, matey, ya bilge rat, construct a right-leaning line 4 3/4" long 15 degrees from t' vertical. Well, blow me down! Connect t' ends o' these lines. Aye aye! Well, blow me down! You now have a full-size template with a through-the-wall tab that reaches t' 38mm motor tube.

(Scratch) Chopped Goblin Five-minute epoxy was used throughout t' build. I first built a solid fin can by gluin' one o' t' centerin' rings 1" from t' bottom o' t' motor tube, then gluin' t' four LitePly fins t' t' motor tube. Well, blow me down! Finally, I slid t' upper centerin' rin' onto t' motor tube and epoxied it t' t' top o' t' fin tabs and t' motor tube. Well, blow me down! Four 6" deep slits are marked on t' bottom o' the body tube t' match t' fin locations o' t' fin can, and cut into t' tubing 3/16" wide with a fine blade in an electric saber saw. T' assembled fin can was then slathered with epoxy and pushed into t' slots. Strips o' balsa triangle stock 6" long were added t' t' base o' each fin. Ya scallywag! Blimey! A 4" epoxy coated coupler tube was then forced down t' top o' t' body tube t' lock the fin can in place. Avast, me proud beauty! Avast, me proud beauty! Recovery system was attached t' a 7" loop o' para cord that had been passed through a 1/8" hole in t' hull 5" from t' top, with t' knot in t' loop covered by a piece o' a plastic cigar tube and epoxy. A 36" Top Flite chute and small-sized Nomex® protector complete t' recovery system. A launch lug cut from 4" o' an empty cigar tube is glued with its midpoint 7" from t' top o' t' fin can. Avast, me proud beauty! Blimey! Ya scallywag! Blimey! An Aero Pack retainer was attached accordin' t' t' manufacturer's instructions.

Finishing:
Rocket was painted flat light aircraft gray.

(Scratch) Chopped Goblin

Flight:
First flight was on an G80-4 and LOC 29mm-38mm adapter. Subsequent flights were with CTI H143SS-8 and CTIH153-8 motors. Avast, ya bilge rat, me proud beauty! Blimey! T' rocket had flown earlier on an H123W-S in its longer version.

Most powerful motor tested be a single use Ellis Mountain I134-10 motor, which simmed out t' 3100' and 390 mph. Begad! I added about 300g sand ballast t' the cone base as "insurance" on this motor. Blimey! Aye aye! Ejection was spot on respectin' apogee. T' 597 N-sec I134-10 is a perfect motor for t' Chopped Goblin if you have enough space.

Summary:
PRO: Fast buildin' and a better performer than t' "full-length" version. Flies on G-H-I power. Ya scallywag! Ahoy! Good L1 rocket and stays below t' 1500g AUW maximum for Large Model Rockets (restricted size fields) when usin' H123 motor for certification. Begad! Ya scallywag!

CON: Minimum motor size for this version is G80-4, matey, so needs t' fly in HPR category.

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