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. Arrr! Avast, me proud beauty! T' particular vehicle modeled is A-001, BP-12, flown on May 13, arrr, 1964. Avast, me proud beauty! Ya scallywag! Each o' t' Little Joe rockets be slightly different in order t' test various aspects o' t' LES system under different flight parameters. Well, blow me down! T' model rocket is constructed usin' commercially available components. Begad! T' service module section (SM) is a LOC 3î diameter body tube. Avast, me proud beauty! T' booster portion is LOC 3" coupler tubin' sections. Begad! Begad! Bulkheads are 1/8" lite ply. Begad! T' capsule and LES tower are constructed in the same fashion as on me Saturn 1b. Arrr! T' fins are made from 1 3/8" aileron balsa strip stock. Ahoy! Arrr! T' corrugated body wrap is vacu-formed and made by a good friend, Paul Graf. Well, blow me down! Blimey! 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. 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). T' various conduit and tunnels are made from strip sheet styrene. T' motor tubes are stock Estes BT-50 body tubes. Begad!

Construction
Construction be fairly easy and straightforward. Begad! T' centerin' rings were hand cut from lite ply since thar were none available in t' motor configuration or diameter required. Well, blow me down! I built t' capsule and LES tower first because I had experience from t' S1b. Begad! 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. Arrr! T' vacu-form wraps were applied usin' 3M77 spray adhesive and t' conduits were applied usin' CA. Well, me hearties, blow me down! 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. Well, blow me down! Ahoy! T' fins were epoxied in place and given a light coat o' finishing resin t' add strength and help seal t' grain. Arrr! Avast! Launch lugs were made from 3/16" I.D. Begad! aluminum tubing. Well, matey, blow me down! The ëUNITED STATES' markin' were made by myself on a Xerox machine. T' ink on t' Microscale decal paper is easily scratched off so I sprayed t' printed decals with a clear fixative. This sealed t' ink and caused no problem during application. Begad!

Finishin' and recovery system
T' only parts requirin' sealin' prior t' paint were t' fins and fiberglassed capsule. Avast! T' booster was painted usin' Krylon's silver. T' SM body tube was finished usin' white monokote trim sheet wrapped around t' body tube. Ya scallywag! The capsule and LES tower were painted with Krylon gloss white. T' black roll pattern markings were made from trim monokote and applied usin' t' patterns found in t' Estes kit. Avast, me proud beauty! Arrr! Since thar be nay much room in t' body tube for the shock cord, ya bilge rat, parachute and waddin' I opted t' use Pratt Hobbies Nomex® protector and do away with t' need for recovery wadding. Avast! 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. Begad! T' parachute is 24" ripstop nylon and the shock cord is a 3 yard length o' 1/2" ribbed elastic. Ya scallywag!

{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. Modelin' on RockSim and AltiCalc showed t' Estes D12-5 t' be t' motor o' choice for clustering. Avast! I have had good success with clusterin' Estes D engines. Begad! Blimey! Altitude prediction with RockSim and AltiCalc showed max altitude around 630' which was pretty good for a rocket o' this size. Ya scallywag! 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. Blimey! Well, matey, blow me down! Blimey! I used Estes long motor hooks for motor retention. Begad! Blimey! This requires t' use o' a spacer in each motor tube but I was usin' what parts I had on hand in me spare parts boxes. Ahoy! 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. Aye aye! Blimey! Blimey! 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. Avast!

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

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

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