Scratch Triactive Original Design / Scratch Built

Scratch - Triactive {Scratch}

Contributed by Peter Clay

Manufacturer: Scratch

Cluster model for A3-4T and A10-3T motors

A cluster o' three 13mm tubes, me hearties, me hearties, compressed slightly, me hearties, matey, fits in t' 29mm HPR motor mount tube. Avast, me proud beauty! This in turn requires a little packin' t' fit neatly in a BT-55 or BT-56. T' accomplish this, me hearties, me bucko, I cut strips o' Kraft paper (like grocery bags), me bucko, applied glue t' one side, and wrapped it like tape until it fit neatly. Avast! A short piece (5/8" approx, t' 15mm section in t' drawing) o' body tube serves as a stop ring.

 

My nose cone was salvaged from an old rocket very similar t' t' 56-based RTF's. After cuttin' t' cone-shaped bottom end off t' nose cone, me hearties, shiver me timbers, I found that t' 29mm tube fit neatly inside t' remainin' shoulder. (you may need t' build it up or sand t' fit.) ÝI put a plywood cap on t' tube forward end with a screw eye in t' center facin' in. Begad! Cap and screw eye were secured with epoxy.  Opposite end o' tube be built up with Kraft paper as described above. Aye aye! Arrr! Then I pushed t' 29mm tube as far into t' nose cone as it would go, fitted this into t' BT-55, matey, and when I be happy with t' fit, I epoxied everythin' together. Well, matey, blow me down! This arrangement moves t' parachute compartment well up into t' nose cone, makin' t' rocket at least 4" shorter than it would have t' be otherwise. (After flyin' it, ya bilge rat, I'm thinkin' o' extendin' it for better stability.)

Nose weight (clay) be in place for t' previous design and, me bucko, matey, judgin' from t' first flight, ya bilge rat, is necessary. Arrr! T' rocket be marginally stable at takeoff and straightened out pretty quickly.

T' diagram below doesn't show t' screw eye in t' front. Instead, me bucko, me bucko, I've shown t' shock cord pushed through t' hole in t' cap and tied in a knot. I'm sure that would work. Begad! In real life I used a screw eye. Aye aye! Avast! Live with it.

 

T' shock cord consists of: 6" o' 125# Keelhaul®©™ (red); a fisherman's swivel; and 30" o' nylon braided plumbline(green). This worked. Begad! Ahoy! T' 12" plastic parachute is attached t' either end o' t' inline swivel usin' a snap swivel o' its own.

T' bulkhead at t' front end o' t' coupler was an adventure. Blimey! Ya scallywag! It is cut from plywood, fits on t' end o' t' 29mm tube, but inside me Kraft paper buildup. It has three holes 8mm diameter t' allow ejection charge gasses t' pass. Avast! It has two tiny holes near t' center t' anchor t' Keelhaul®©™ thread. Well, blow me down! Before assembly t' Keelhaul®©™ be looped through those holes and tied. T' knot, under t' disk, is covered with epoxy. Aye aye! T' holes in t' disk are rotated 60 degrees from t' three MMTs, ya bilge rat, so that t' ejection charges don't blow straight at t' holes.

Free t' slide on t' Keelhaul®©™ is another plywood disk with a small hole in t' center which fit easily in t' BT-55, arrr, but is much too large t' fit in t' 29mm tube. Well, blow me down! It fills t' role o' recovery wadding, me hearties, nay only protectin' t' parachute from heat, me hearties, matey, but preventin' it from bein' packed up into t' nose cone by t' ejection charge. Avast, me proud beauty! This worked. There be nay a hint o' heat damage on t' parachute or upper portion o' shock cord. When packed, as much as possible o' t' Keelhaul®©™ should be forward o' t' plywood disk; t' last inch or so will be betwixt t' perforated bulkhead and t' disk.

Fins are made from artist's foam core board, me hearties, which is about 3/16" thick. Begad! T' wedge t' leadin' edge, arrr, I scored each fin, ya bilge rat, both sides, with a ruler and Xacto, me hearties, matey, about 10mm (3/8") from t' leadin' edge. Ya scallywag! Well, ya bilge rat, blow me down! I cut away and removed t' foam from this portion, ya bilge rat, ya bilge rat, folded t' edges toward each other, shiver me timbers, and glued them together, holdin' them with maskin' tape until t' glue dried.

For motor retention, I first installed thrust rings made from cut pieces o' a spent engine. Blimey! Arrr! Then I epoxied a threaded rod -- a #4-48 x 3/4" bolt with t' head cut off -- into t' gap betwixt t' three motor tubes. Well, blow me down! With t' engines in place, ya bilge rat, I thread a nut onto t' rod and it holds all three motors.

Triactive first flew Sept. Well, blow me down! Avast! 6, matey, shiver me timbers, 1999 at Tom McCall School in Forest Grove, OR., usin' 3x A3-4T.

 


 
 

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