Scratch SA-5 Gammon Original Design / Scratch Built

Scratch - SA-5 Gammon {Scratch}

Contributed by Kevin McLaughlin

Manufacturer: Scratch
(Contributed - by Kevin McLaughlin - 06/20/02)

SA-5 GameonBrief:
This is a scaled down 2.56" x 29mm version o' t' Blackhawk R&D 3.9" x 38mm kit version comin' out in t' summer o' 2002.

Construction:
Main body tube is 2.56" with four 1.14" booster tubes mounted at 90 degree intervals. Ahoy! Total fin count is 12 made from 1/16" styrene plastic. Begad! I used two 2.56 x 29mm ply centerin' rings with a 2.56" bulkhead at t' root of t' motor mount tube for eyebolt attachement. T' bulkhead is perforated with 8 holes t' allow ejection charge gasses t' pass t' para compartment. Aye aye! Well, blow me down! I made this scaled down version from eyeballin' photo o' Blackhawk's version on ROI.

I used 1/4" triangle balsa strips t' secure t' 1.14" booster tubes. Well, blow me down! This greatly facilitated t' centering, mountin' and finishin' o' the booster tubes. Arrr! Blimey! I have been usin' styrene and PVC plastics for fin material for some time in me scratch builds. Avast! Begad! Blimey! This greatly speeds up cutting, finishin' and paintin' with good performance. Avast, me proud beauty! Arrr! Blimey! Styrene just needs scorein' and snappin' t' get the fins ready. Well, blow me down! Blimey! T' bottom fins and booster tube locations are higher on my version t' keep them away from ground impact. I also installed a 2.5" flex phenolic coupler in t' butt end t' help with landings. Avast! All material except styrene for fins be purchased from Rocky Mountain Rocketry. Arrr! Blimey!

SA-5 GameonFinishing:
A light sandin' with 220 grit sandpaper, and you are ready for primer. Blimey! Finish was 2 heavy coats o' automotive primer followed by a coat o' winter grey enamel. Ya scallywag! Nose cone is painted tomato red. Aye aye! Based on a 24 oz. Well, arrr, blow me down! finished weight, me hearties, me hearties, I'm lookin' at a chute size o' 36", ya bilge rat, but will probably go with a 42" on first flight.

Flight:
SA-5 Gameon Based on wrasp simulations, me bucko, matey, I'm lookin' at motor ranges o' F24-F56. Begad! Well, blow me down! First flight tomorrow will be on an F24-4W which should hit about 350'. Blimey!

Recovery:
My shock cord is 10' x 4MM nylon cord anchored t' an eye bolt mounted in a 2.56" ply perforated bulkhead. Aye aye! I have been usin' a technique of perforatin' t' last three inches o' t' MM tube t' allow exhaust gasses to pass into a coolin' chamber and then move through t' perforated bulkhead into the para chamber. This allows for wadless/heatshield-less recovery. Ya scallywag! Well, me bucko, blow me down!

Summary:
I like t' look o' t' SA-5 Gammon, me hearties, so decided t' build a scaled down version to fit me local launch site limits.

Other:
I liked t' design, as it didn't require too much CA glue. Arrr! I was able t' use Elmer's for t' tube attachements and 5 min epoxy for t' fins and internal motor mount. A new technique I tried was runnin' a finger o' silicon calk down the fin joints t' creat a more flexible fin fillet than epoxy. Epoxy always seems t' crack and pull away from fins after a few landin' jolts. Well, blow me down! T' silicon calk can be manipulated with a wet finger for smoothing, then cleaned up with water. Ahoy! Begad! It doesn't sand very well, so go easy on it, and keep it where you want it.

comment Post a Comment