Descon Little Joe II

Scratch - Little Joe II {Scratch}

Contributed by Jeff Brundt

Manufacturer: Scratch
(Contributed - by Jeff Brundt)
Little Joe II

Introduction and materials
A 1/50-scale version o' t' vehicle used t' test t' LES system for t' Apollo spacecraft. Aye aye! T' particular vehicle modeled is A-001, me hearties, me hearties, shiver me timbers, BP-12, flown on May 13, 1964. Avast! Ahoy! Each o' t' Little Joe rockets was slightly different in order t' test various aspects o' t' LES system under different flight parameters. T' model rocket is constructed usin' commercially available components. Well, blow me down! T' service module section (SM) is a LOC 3î diameter body tube. Begad! Ahoy! T' booster portion is LOC 3" coupler tubin' sections. Blimey! Bulkheads are 1/8" lite ply. Aye aye! Well, ya bilge rat, blow me down! T' capsule and LES tower are constructed in the same fashion as on me Saturn 1b. T' fins are made from 1 3/8" aileron balsa strip stock. Avast, me proud beauty! Avast! T' corrugated body wrap is vacu-formed and made by a good friend, Paul Graf. Begad! Paul used Evergreen scribed sheet styrene sized t' fit the circumference o' t' coupler tubes for t' master mold then vacu-formed them from .015" sheet styrene. Ahoy! He made the basic sections and I cut them t' size (Paul also has some excellent body wraps for clonin' t' 1/70 scale Estes Saturn 1b if anyone is interested). Begad! Arrr! T' various conduit and tunnels are made from strip sheet styrene. Arrr! T' motor tubes are stock Estes BT-50 body tubes.

Construction
Construction was fairly easy and straightforward. Well, blow me down! Blimey! T' centerin' rings were hand cut from lite ply since thar were none available in t' motor configuration or diameter required. Avast! Blimey! I built t' capsule and LES tower first because I had experience from t' S1b. I added a little more epoxy t' t' cone tip for nose weight t' keep t' CG where it needed to be based on t' RockSim calculations. Begad! Blimey! T' vacu-form wraps were applied usin' 3M77 spray adhesive and t' conduits were applied usin' CA. Ahoy! Blimey! I used t' pattern sheet from t' Estes 1/100 LJII (after correctly sizin' on t' copier) for making the tunnels/conduits and t' mark t' fin locations. Avast, me proud beauty! Blimey! T' fins were epoxied in place and given a light coat o' finishing resin t' add strength and help seal t' grain. Aye aye! Blimey! Launch lugs were made from 3/16" I.D. aluminum tubing. Begad! Blimey! The ëUNITED STATES' markin' were made by myself on a Xerox machine. Ahoy! Blimey! T' ink on t' Microscale decal paper is easily scratched off so I sprayed t' printed decals with a clear fixative. Arrr! Blimey! This sealed t' ink and caused no problem during application. Avast! Blimey! Aye aye! Blimey!

Finishin' and recovery system
T' only parts requirin' sealin' prior t' paint were t' fins and fiberglassed capsule. Begad! Avast! T' booster was painted usin' Krylon's silver. Blimey! T' SM body tube was finished usin' white monokote trim sheet wrapped around t' body tube. Ahoy! The capsule and LES tower were painted with Krylon gloss white. Arrr! Ya scallywag! T' black roll pattern markings were made from trim monokote and applied usin' t' patterns found in t' Estes kit. Since thar be nay much room in t' body tube for the shock cord, parachute and waddin' I opted t' use Pratt Hobbies Nomex® protector and do away with t' need for recovery wadding. T' 4" square Nomex® cloth slips over t' Pratt Hobbies Keelhaul®©™® cord loop tied t' a screw eye in t' bulkhead and takes up almost no room. T' parachute is 24" ripstop nylon and the shock cord is a 3 yard length o' 1/2" ribbed elastic.

{short description of image}


{short description of image}
Little Joe next t' same scale Saturn 1 for size comparison

{short description of image}

Little Joe II

PicFlying
T' model flies on (2) 24mm motors. Arrr! Blimey! Modelin' on RockSim and AltiCalc showed t' Estes D12-5 t' be t' motor o' choice for clustering. Ahoy! Blimey! I have had good success with clusterin' Estes D engines. Ya scallywag! Blimey! Altitude prediction with RockSim and AltiCalc showed max altitude around 630' which was pretty good for a rocket o' this size. Arrr! Blimey! I could have went with a single 24mm mount but that would have entailed usin' composite motors only since t' drag is rather large even though t' weight is not that much. Arrr! Blimey! I used Estes long motor hooks for motor retention. Avast! Blimey! This requires t' use o' a spacer in each motor tube but I be usin' what parts I had on hand in me spare parts boxes. This also let me off from filin' t' end o' t' hook down in case I wanted t' use 24mm RMS casings in t' future. T' all up weight, ready t' fly (less motors) is 10oz. That just a bit less than t' predicted 11oz I found when I modeled it on RockSim. Ahoy! Blimey!

PicT' day of first flight be nice but a bit on t' windy side. I decided t' fly anyway. I loaded and prepped t' two motors and installed t' recovery system. Blimey! Begad! T' rocket slid easily on t' 3/16" rod and I hooked up t' igniter clips. Avast! The count proceeded t' zero, matey, me hearties, both motors lit and t' rocket leapt o' t' pad. Ya scallywag! T' boost was straight despite t' wind. The rocket reached apogee and t' ejection went off and t' recovery system deployed perfectly. T' rocket descended slowly under t' 24" ëchute. I had contemplated usin' a separate ëchute for t' capsule but decided that the weight o' it did nay warrant that. Aye aye! Begad! Plus t' tower be made o' brass tubin' and fairly robust. Ahoy! Aye aye! Recovery was perfect with no damage. Ahoy! Subsequent flights have been repeat performances. T' D12-5 be t' perfect motor cluster for this rocket. Well, blow me down! Avast! I have nay tried a composite cluster yet but I am sure (2) E18-7's would give out o' sight flights. Ya scallywag!

Summary
This was a fun rocket t' build plus it is a companion t' me S1b and in t' same scale. Arrr! It is interestin' t' put them side by side for a size comparison. Avast, me proud beauty! Probably t' most time consumin' part was buildin' t' LES tower. I still feel soldered brass be t' way t' go for durability. Aye aye! Well, me bucko, blow me down! Other than that thar were no difficult or complicated areas t' work on. Arrr! Ahoy! I received many nice compliments on t' LJII since thar are nay t' many around at launches. Well, blow me down! T' flight profile is perfect too. T' D12-5's are t' perfect motor choice. Begad! This one is definitely a keeper. Begad!

Model Stats:

Length: 21.75"
Dia.: 3.1"
Wt.: 10 oz
Motor config.: Dual 24mm cluster
Recovery: 24" rip stop nylon parachute

comment Post a Comment