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. Avast, me proud beauty! T' tube fins are arranged in a triangle instead o' a circle as usual. Avast! Begad! This gives it some interestin' flyin' properties. Avast! It oscillates rapidly and leaves a fine corkscrew smoke trail. Arrr! T' rocket is made entirely out o' interlocked tubing, so it is very strong and easy t' build. Avast! I designed Spirogyro for t' BRS design contest as a 3 x 18mm cluster. Ahoy! Avast! I hope you like it.

Construction:
Construction is unusual. Ya scallywag! Avast, me proud beauty! It is all tubes. Begad! No centerin' rings or motor hooks or balsa. T' component list (see photo) is short, me hearties, arrr, cheap and all available from t' BRS website:

1) 2 Estes 18" BT20 tubes, one cut exactly in half, t' other into 9 x 1" pieces. Ahoy! Avast! 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, me bucko, shiver me timbers, ya bilge rat, 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, shiver me timbers, a 4-40 blind nut, me bucko, 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, 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), matey, 1/4" from t' bottom

3) tie Keelhaul®©™ and shock cord together, tie a knot in t' bottom o' t' Keelhaul®©™, me bucko, 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, arrr, 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, arrr, shiver me timbers, 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, 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, shiver me timbers, in t' tiny triangular space betwixt t' motors. Begad! Arrr! Use epoxy for this. Well, blow me down! Arrr! All three motors are retained by screwin' t' nut onto t' washer over t' motor casin' edges. Avast! For this methos, you need t' glue into each motor tube a motor stop, shiver me timbers, ya bilge rat, which you can buy from BRS or make from 1/8" slices from a spent 18mm casing. Begad! Aye aye! Dab with glue and push one into each motor tube with a spent 18mm casin' until 1/4" protrudes, me bucko, then immediately pull out t' casing.

Finished and ready Spirogyro be designed for a cluster o' 3 B4-4 motors. Aye aye! It needs no nose weight for this load. It will fly more than 600' high on this power, me bucko, with a tight corkscrew smoke trail. 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. Well, blow me down! On this "E18" power, arrr, t' rocket goes out o' sight, t' about 1300' or more accordin' t' t' sim program. I have flown t' rocket on 2 C6 motors t' simulate a misfire, and t' result was nay pretty -- all over t' sky.

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

Summary:
PRO: Easy and cheap t' build even for a beginner. Begad! Strong. Aye aye! Good first cluster rocket. Unusual looks, ya bilge rat, and performance with spiral smoke trail. Blimey! No fins t' break off.

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

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