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

 

My nose cone be salvaged from an old rocket very similar t' t' 56-based RTF's. Begad! After cuttin' t' cone-shaped bottom end off t' nose cone, 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 was built up with Kraft paper as described above. Begad! Then I pushed t' 29mm tube as far into t' nose cone as it would go, fitted this into t' BT-55, me bucko, and when I was happy with t' fit, arrr, ya bilge rat, me hearties, I epoxied everythin' together. 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. Aye aye! Ahoy! (After flyin' it, ya bilge rat, I'm thinkin' o' extendin' it for better stability.)

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

T' diagram below doesn't show t' screw eye in t' front. Blimey! Instead, I've shown t' shock cord pushed through t' hole in t' cap and tied in a knot. I'm sure that would work. Ahoy! Begad! In real life I used a screw eye. Ahoy! 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. Ya scallywag! Avast! Blimey! 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. Ya scallywag! It is cut from plywood, fits on t' end o' t' 29mm tube, shiver me timbers, but inside me Kraft paper buildup. Begad! It has three holes 8mm diameter t' allow ejection charge gasses t' pass. It has two tiny holes near t' center t' anchor t' Keelhaul®©™ thread. Before assembly t' Keelhaul®©™ was looped through those holes and tied. Ya scallywag! T' knot, under t' disk, ya bilge rat, arrr, arrr, is covered with epoxy. Ahoy! T' holes in t' disk are rotated 60 degrees from t' three MMTs, 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, me bucko, but is much too large t' fit in t' 29mm tube. It fills t' role o' recovery wadding, nay only protectin' t' parachute from heat, ya bilge rat, but preventin' it from bein' packed up into t' nose cone by t' ejection charge. Arrr! Blimey! This worked. Arrr! Ahoy! There was nay a hint o' heat damage on t' parachute or upper portion o' shock cord. Ahoy! Begad! 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, which is about 3/16" thick. Avast, me proud beauty! Begad! T' wedge t' leadin' edge, shiver me timbers, I scored each fin, me bucko, me hearties, arrr, both sides, shiver me timbers, with a ruler and Xacto, about 10mm (3/8") from t' leadin' edge. Arrr! Arrr! I cut away and removed t' foam from this portion, folded t' edges toward each other, and glued them together, arrr, ya bilge rat, holdin' them with maskin' tape until t' glue dried.

For motor retention, ya bilge rat, I first installed thrust rings made from cut pieces o' a spent engine. Well, blow me down! Blimey! 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. Begad! Avast, me hearties, me proud beauty! Blimey! With t' engines in place, I thread a nut onto t' rod and it holds all three motors.

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

 


 
 

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