Scratch - Bad Medicine {Scratch} Original Design / Scratch Built

Contributed by Ted Phipps

Manufacturer: Scratch
(Contributed - by Ted Phipps)

This is a scratch-built tube-finned design built mainly from scavenged materials. Someone at work had salvaged some cardboard tubing that was 2.25" diameter, and left it on my desk (I encourage that sort of behavior at work). It was very thick (1/8" walls!) and heavy, and not particularly suitable for rocketry, so it sat around in my basement for quite a while, becoming a spider-habitat.

Rocket Pic

After a nasty summer cold, I was stumbling around the house, still too sick to go back to work but tired of lying in bed and feeling miserable. I wandered downstairs and decided to build a rocket. My mood wasn't suited to precision, so I decided to throw together a quick, cheap, and crude beast that might never even fly. Fins were out – too much trouble – and I didn't really want to waste good parts on this because I had no idea what the results would be, so I dug out that salvaged tubing and evicted most of the eight-legged residents.

To match the ‘spirit' of the design, I decided to go with a 29mm motor mount and fly her on Econojets, probably G's because of the anticipated weight. I cut a short length of motor tubing (the only real ‘rocket' component used) and then made centering rings out of thick cardboard salvaged from the cover of an old 3-ring binder. All construction was with Elmer's yellow glue except as noted.

Next came the tube-fins. If you are a precision fanatic or detail-oriented type, you might want to skip the rest of this paragraph. I took another length of that tubing, marked it off into 16" sections, and then cut those in half on 45 degree angles using a scroll saw – freehand. The tubes are all slightly different lengths and the angles aren't quite all the same, but they're all close enough. Mounting them with the angle facing back and the flat ends even with each other masked the imperfections.

The shock cord mount is a throwback to the early days of rocketry. I cut two slots in the tube up near the nose and threaded the shock cord (1/4" tubular nylon) through them, with a knot on the inside to keep it attached. The tube itself is thick enough that I shaved a little out on the outside so that the exposed shock cord is almost flush with the airframe.

The nose cone was by far the most involved part of construction. It was formed from a styrofoam cone used for flower arrangements. Roll the cone against a table top or other hard surface to gently crush it to shape and diameter. A short length of body tube was fitted as the bottommost cone section, and another short length with a thin segment removed became the nose cone shoulder and coupler.

Weight was needed at the nose to balance out those heavy tube fins, so epoxy was used for all nose cone construction. Several fishing weights were pushed into the foam, followed by a layer of epoxy to lock them into place. Next I bent a piece of coat hanger into a loop and drilled small holes into the nose cone shoulder to fit the ends. More 5-minute epoxy puddled in around the attachment points made the loop solid and permanently attached. There's quite a bit of epoxy in there, which is what I needed to move the center of gravity forward.

Finally I smeared the entire cone with Elmer's Fill ‘n' Finish, sanded and filled again until I was satisfied (and I was easy to please), then coated the FnF with thin CA to toughen it up some.

Finishing was accomplished by spraying a coat of white primer all over – and then watching the cardboard soak it up like a sponge. Another coat, same results… Ok then, the job calls for fluorescents! I shot the paint as shown in the picture – yellow first, and then the pink, overlapping to get orange. The black parts of the tube fins is Testor's flat black from those tiny bottles, slopped on with a small brush. Once everything was dry, I used a permanent laundry marker to write the name on the rocket. After a week of fighting that cold with seemingly every over-the-counter concoction ever developed by man – none of which made me feel any better – ‘Bad Medicine' just seemed appropriate.

Flight Report

Final empty weight is 28 ounces, which is quite hefty for a rocket of this size. Total length is about 40 inches.

She's made two flights so far, both on G38 Econojets. The 7 second delay is a little long, and the 4 second is a bit short, but either one works because this rocket is solid. Motor retention is friction fit, and she's nicely recovered on a 30" nylon chute. On windy days, I wouldn't hesitate to go with a smaller chute to minimize drift.

This is like that old car that runs great but isn't much to look at. I expect that I'll be flying the Bad Medicine for years to come on those cool and rude Econojets. And if I ever lose her to the rocket gods, I'll just build another tube-fin and keep on launching.

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