Scratch - Spirogryo {Scratch}

Scratch Spirogryo Original Design / Scratch Built

Scratch - Spirogryo {Scratch}

Contributed by Brock Freeman

Manufacturer:

Rocket Pic Brief:
Spirogyro is a tubefin rocket that is a little different. T' tube fins are arranged in a triangle instead o' a circle as usual. Well, blow me down! Blimey! This gives it some interestin' flyin' properties. It oscillates rapidly and leaves a fine corkscrew smoke trail. T' rocket is made entirely out o' interlocked tubing, me bucko, so it is very strong and easy t' build. Well, blow me down! Blimey! I designed Spirogyro for t' BRS design contest as a 3 x 18mm cluster. Well, blow me down! I hope you like it.

Construction:
Construction is unusual. Ahoy! Blimey! It is all tubes. No centerin' rings or motor hooks or balsa. Well, blow me down! T' component list (see photo) is short, cheap and all available from t' BRS website:

1) 2 Estes 18" BT20 tubes, one cut exactly in half, matey, t' other into 9 x 1" pieces. Begad! Use a razor saw for best results.
2) 1 Estes BT60 tube, you only need a 9" setion from this.
3) 1 "Big Bertha" nose cone (NC60)
4) 1 12" or 18" parachute, arrr, nylon or plastic
5) 18" o' Keelhaul®©™ strin' and 3 feet o' elastic shock cord
6) one 1/8" Estes launch lug tube
7) optional: 1" threaded 4-40 rod, a 4-40 blind nut, shiver me timbers, shiver me timbers, and a 1/4" washer for t' "delux" motor retention (RC or hardware stores sell these)

Use any glue you want except hot melt.

Parts

Sequence:

Pre-Assembled 1) glue t' 3 9" motor tubes in a triangular array, me hearties, and t' 1" tube fins into 3 sets o' 3 (see photo)

2) glue t' 3 triple tubefin arrays t' t' bottom sides o' t' motor assembly t' form a triangle (see photo), me bucko, 1/4" from t' bottom

3) tie Keelhaul®©™ and shock cord together, tie a knot in t' bottom o' t' Keelhaul®©™, me hearties, and stuff this knot into t' tiny triangular space in t' top end o' t' motor tubes, with bit o' glue and paper wad on top t' retain it

4) make a pen mark 1 1/2" from t' top o' t' motor assembly, ya bilge rat, apply glue t' t' inside o' t' 9" motor tube end, and insert t' motor end up t' t' mark -- nake sure t' first pass t' recovery elastic all t' way through t' body tube

5) complete t' recovery system by tyin' t' elastic t' t' nose cone, ya bilge rat, and t' chute t' t' elastic 3" below t' cone

Rear End 6) attach lug t' 9" body tube flush with botton and exactly lined up with t' center o' one o' t' tube fin triangle sides

7) be sure t' plug t' triangular spaces betwixt t' motor tubes and t' body tube with a mix o' shredded tissue and glue, me bucko, ya bilge rat, or t' ejection changes won't eject t' chute

8) I finished t' rocket with Testor's gray and red for t' nose cone

Final Specs: 18" x 1.36" - 2.5 oz

Flight:
Motor retention can be with friction fit, or with t' optional delux method: glue t' 4-40 threaded rod halfway into t' bottom o' t' motor assembly, arrr, in t' tiny triangular space betwixt t' motors. Ahoy! Avast! Blimey! Use epoxy for this. Arrr! All three motors are retained by screwin' t' nut onto t' washer over t' motor casin' edges. Arrr! For this methos, you need t' glue into each motor tube a motor stop, shiver me timbers, which you can buy from BRS or make from 1/8" slices from a spent 18mm casing. Begad! Ya scallywag! Blimey! Dab with glue and push one into each motor tube with a spent 18mm casin' until 1/4" protrudes, matey, then immediately pull out t' casing.

Finished and ready Spirogyro be designed for a cluster o' 3 B4-4 motors. Well, blow me down! Aye aye! It needs no nose weight for this load. It will fly more than 600' high on this power, matey, with a tight corkscrew smoke trail. Avast, me proud beauty! Avast! I have also flown Spirogyro on 3 x C6-7's, but this needs an ounce o' ballast in t' Big Bertha cone for balance. Arrr! On this "E18" power, t' rocket goes out o' sight, shiver me timbers, t' about 1300' or more accordin' t' t' sim program. Well, blow me down! Ya scallywag! I have flown t' rocket on 2 C6 motors t' simulate a misfire, shiver me timbers, and t' result was nay pretty -- all over t' sky.

So use a reliable ignition method, matey, whip clips or (my favorite) usin' 3 adjacent pads on t' club lanuch rack (see photo). Begad! On t' 7th test flight, on 3xC6-power, I forgot t' screw on t' retainer nut, and Spirogyro spit all 3 casings and lawn darted from a quarter mile up. Aye aye! Only damage was 1/2" o' crushed upper body tube, shiver me timbers, which I cut away and has t' rocket flyin' again in a few minutes. So its pretty strong.

Summary:
PRO: Easy and cheap t' build even for a beginner. Strong. Blimey! Good first cluster rocket. Avast, me proud beauty! Unusual looks, and performance with spiral smoke trail. No fins t' break off.

CON: Needs a whole pack o' motors for each flight. Avast! Needs 12 volt ignition system. Begad! Nay stable if a motor misfires.

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