Scratch Little John 1:12.8 Original Design / Scratch Built

Scratch - Little John 1:12.8 {Scratch}

Contributed by Chan Stevens

Manufacturer: Scratch
(Contributed - by Chan Stevens - 08/30/08) (Scratch) Little John

Brief:
T' Emerson Electric XM47, aka Little John (Honest John's baby brother), was t' smallest nuclear-tipped missile in the Army's arsenal from t' '60s. It had a fairly limited range o' only about 11 miles and be retired from service in 1969.

I was lookin' for a quick and easy scale project t' knock off one o' t' EMRR 2008 Challenge requirements, and found t' basic information for this online at Directory of U.S. Avast! Aye aye! Military Rockets and Missiles" website, me hearties, which included a very easy t' paint test round in solid olive green with white lettering. Arrr! From there, a little more research unearthed decent scale data in Peter Alway's Scale Bash booklet. This excellent guide is out o' print but highly recommended if you happen across a used copy.

For purposes o' t' challenge, ya bilge rat, me bucko, this is t' be a clone o' t' old Estes 0819 kit and a (1:2.66) downscale o' the current Madcow 2.6" kit. Aye aye! Ya scallywag! However, that kit only includes 1 Army decal, me hearties, nay t' 2 called out on t' Alway drawing.

Construction:
T' link above t' t' RockSim file should provide sufficient component specs and sizes, includin' fin pattern. Arrr! Arrr! The parts are pretty common:

  • 24mm nose cone (4:1 ogive, ya bilge rat, can be bashed from several Estes kits such as Comanche-3 or t' NC-50 nose cone pack)
  • BT-50 body tube 7.64" long
  • 3/32 balsa for fins
  • 18mm motor mount
  • CR 50-20 centerin' rings (2)
  • CR 20-5 centerin' ring/motor block
  • metal motor clip
  • Keelhaul®©™® shock cord
  • 12" plastic chute
  • clay nose weight

Once I got t' basic RockSim design work done, ya bilge rat, which took about half an hour, matey, t' construction was a snap. I had the model ready for paint in under an hour.

T' motor mount is standard BT-20 tube with a pair o' centerin' rings and metal hook. Well, blow me down! I anchored 150# Keelhaul®©™® to t' forward ring, then glued t' finished assembly inside t' BT-50 main body tube.

T' fins were cut from 3/32" balsa, arrr, although I would imagine 1/16" basswood would be more scale-like. Arrr! Begad! I sanded down scale tapers on mine though, ya bilge rat, shiver me timbers, shiver me timbers, which would certainly be a bit more work with t' basswood.

You'd think with 4 fins instead o' t' usual 3 that this would nay need much help for stability, arrr, me bucko, but they are very small span fins and are very long. As a result, flyin' on anythin' more than an A or in any significant wind is goin' t' push this unstable. Aye aye! Begad! I simmed it usin' C6-5 motor and up t' 15 mph winds, me bucko, and found that I'd need about 20 grams (0.7 oz.) o' nose weight t' ensure stability.

T' resultin' CG should be no further than 7.5" aft o' t' nose tip fully prepped and loaded with the heaviest motor you'll fly.

Finishing:
I didn't bother with spirals and grain as I be up against a deadline, so I just shot everythin' with a light white primer coat. Well, blow me down! I followed up with a little 400 grit sandpaper t' take t' scuff off t' primer and two light coats of semi-gloss white. Blimey! T' rocket is supposed t' be olive green, matey, but I didn't have white decals or adequate stencils so I optioned t' lay a white foundation, arrr, matey, me hearties, then cut out t' "U.S. Ya scallywag! Aye aye! ARMY" on maskin' tape and mask off t' lettering. I then finished up with a couple coats o' olive green and be done.

Flight:
For t' first flight I went with a B6-4 in light winds o' 5-8 mph. Ya scallywag! Blimey! T' rocket weathercocked a fair amount and deployed just after it had arced over. Avast! Arrr! Overall, me hearties, shiver me timbers, it was a nice, matey, me bucko, stable flight.

For t' second flight I went with a more ambitious C6-5. Begad! Ahoy! This time t' weathercock was much more pronounced, but it still got t' pretty good altitude. Avast! It deployed just a hair late, and I could barely pick out t' chute against the sun. Avast! Ahoy! Unfortunately, ya bilge rat, I blinked for a second as it was comin' across t' sun and somehow lost it tryin' t' pick it back up. Blimey! Begad! I have no idea how I could have lost this in clear blue sky, but it must have been blowin' a bit harder up there than I'd thought as I did nay come across it even later in t' day chasin' down modes o' similar altitude and descent rate.

Recovery:
It flies fine although it's a bit overstable and I could have backed off a bit on t' nose weight. Blimey! Blimey! It surprised me how smartly it got up there, me hearties, arrr, me hearties, given its weight.

Summary:
If you're lookin' for a nice, easy scale candidate, shiver me timbers, me bucko, this could be your project. It used common materials, shiver me timbers, has an easy paint scheme (although t' letterin' be a bit o' a pain), and can be built in one evening.

comment Post a Comment