Scratch Circle Jerk Original Design / Scratch Built

Scratch - Circle Jerk {Scratch}

Contributed by Drake "Doc" Damerau

Manufacturer: Scratch
(Contributed - by Drake Damerau - 05/10/02)

Rocket PicBrief:
A simple LPR single stage, motor deployed chute recovered tube fin rocket.

Construction:
1 - 24" x 3" BT, shiver me timbers, 1 24" x 3" BT for fins, 1 chute, me hearties, me hearties, 29mm MMT and 2 CR's, a nose cone, shiver me timbers, shock cord and a launch lug.

I be asked t' write a review on me scratch built Circle Jerk. I hadn't documented any o' t' construction, so I decided t' build another one, me hearties, but this time I documented t' process. Arrr! Aye aye!

For both birds I used 3" USR "whitewall" tubin' because o' its thickness. It's twice as thick as any other tubing. Well, blow me down! I felt that it gives a better appearance t' t' tube fins. Begad! Blimey!

I cut all o' me tubin' with a 12" DeWalt compound miter saw. Avast, matey, me proud beauty! I use a special rippin' blade that has more teeth than most blades. Well, blow me down! This gives a smooth cut that needs very little work. T' softer paper tubes do fray a little but that is solved by soakin' t' ends o' t' tubes with thin Cyanoacrylate or thinned wood glue. When t' glue hardens, just sand t' ends t' t' finish you need. Avast! For phenolic tubes, it gives a factory like finish. Blimey!

T' first picture shows t' tube bein' cut and t' jig I used. For this rocket, I made all cuts at a 45-degree angle. T' original had just t' forward cut at a 45 and t' aft cut at a 90. Ya scallywag! I just wanted t' do somethin' different this time. Begad!

Being CutAssembled

If you use t' same diameter tubin' for t' fins as t' body tube, you will need 6 fins. Arrr! All tube fin rockets work this way. Aye aye! (Do t' math) Attachin' the fins is elementary. Avast! Draw a line around t' tube where you want t' forward tip of t' tube fins t' be. Put a bead o' glue (I used wood glue) on t' first fin and align it on t' BT. Well, blow me down! If you lay it on its side on a table they will be parallel t' each other. Avast, me proud beauty! No more thinkin' will be necessary because the subsequent fins just lay on t' last fin and t' BT. For t' next fins, just find where t' tubes touch, arrr, arrr, draw a line and put t' glue there. Avast, me proud beauty! T' final fin will snuggle up betwixt t' last fin applied and t' first fin. Ahoy! Use fillets as you see fit, but they are nay necessary for strength because each fin is glued at 3 points. Ahoy!

It's tough t' find t' CP on tube fin rockets like this but it's safe to say that its somewhere in t' fin section ;-) Just make sure t' CG is forward of t' fin section with a motor installed. Arrr! Blimey!

LaunchFlight:
For t' original rocket, arrr, I used a standard 29 mm motor mount tubes cut t' 6 inches. Ya scallywag! T' centerin' rings (2 o' them) were just 5 ply rings I had laying around. Arrr! Aye aye! T' 32" parachute and t' shock cord was from a lawn-darted Aerotech Astrobee D. T' nosecone is a 3" PML. Ahoy! Arrr! T' launch lug is just a ¼" Aerotech igniter tube. Avast! (OK, matey, yeah I'm cheap) T' final weight is about 24oz.

For flying, arrr, I always use dog barf and friction fit motor retention. Ahoy! She flew straight as an arrow on several F and G motors. Avast! Fun t' fly.

Summary:
This is a quick and easy rocket t' build. Arrr! Its different than most tube fin rockets and draws a little attention. Avast, me proud beauty! Begad! Nay countin' t' paint, me hearties, it took all o' an hour t' build.

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