odd-rocs: the weird, wacky funny side of model rocketry ... · odd-rocs: the weird, wacky funny...

Odd-Rocs: The weird, wacky funny side of Model Rocketry

Tech-Tip 014 Dedicated to the dissemination of detailed model building methods and techniques.

Materials and methods presented here are not intended as the best or only solutions to the modeling challenge(s) discussed, rather as methods and procedures which have a proven record of success in actual use. Please keep experimenting with new materials and techniques as this is the only way to expand the fields of knowledge. Written by: John E. McCoy Sr. NAR-15731 - June 05, 2002, Update: Sept. 30, 2015, Rev.-April 22, 2016

Odd Roc Prototypes and construction are limited only your imagination. An aeronautical engineer once mused to me “Anything will fly, given enough thrust”. I must say that statement may be a tiny bit “outside the Box” but for our purposes here it fits very nicely. Odd rocs by nature are normally not great performance birds. They are novel, funny, creative and some times a little scary expressions of our wild exuberance to power any and everything by repulsion. Some Construction ideas to consider:* After picking the subject prototype do a rough pencil drawing of the model and guess the fin size and placement. * Decide on three, four or more fins, what material they will be and best method of attachment. * Weigh the parts, all the parts, separately if necessary, but have a good idea of the vehicle weight. This will help in selecting motor impulse and thereby internal tube(s) size. * Make a cardboard cutout of the shape to get a general idea of the lateral CP, this will help size or resize the fins, nose weight etc. * Check material; are they compatible with each other and the adhesives, epoxies and glues anticipated in construction of this project? Test all questionable materials and mountings on scrap parts. * Provide room for the recovery system. I can’t tell you how many times I’ve built an Odd Roc assuming a standard chute, and found the finished model to heavy for plastic, than having to struggle to get a rip-stop nylon or silk chute to fit. * Is asymmetry a problem? Off-set thrust can be a major problem. A good example is the Pan-Am Space Clipper Orion from the Movie “2001”. The centerline of the motor thrust is almost 3/8” off the centerline of the model. How do we compensate for this? This problem can only be corrected by oversize fins, and very careful alignment with the main body. I’ve seen instructions telling the builder to “gently cant” by a degree or two, the motors toward the centerline of the model, Guys this only works if you are using multi motors, canted to the center of a symmetric model. Canted motor(s) will NOT WORK on an asymmetrical model. * Some Odd-Roc’s are Plastic Model Conversions, But NOT all PMC’s are Odd-Roc’s. * Make centering rings, as light weight as practical, three heavy cardstock rings are better then two heavy plywood rings. The adhesive bead at the ring-tube joints and fillets create the strength. * On larger, heavier 12oz and over Odd Rocs, fix everything with epoxy, not CA, the epoxy has a little flexibility during hard landings CA simply can’t handle. CA becomes brittle shortly after curing. * Shock cords should be thicker and a least 36” long, anchor to the motor mount with 100lb Kevlar. * Safety note: All new Odd-Rocs should make their first flights with a few people around as possible. Heads Up warnings just isn’t enough for these mostly unpredictable maiden voyages. Hope these suggestions help. 1

Odd-Rocs: The weird, wacky funny side of Model Rocketry

odd-rocs: the weird, wacky funny side of model rocketry ... · odd-rocs: the weird, wacky funny...

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