Sport Rocketry

SPORT ROCKETRY JANUARY/FEBRUARY 2020 19 Pin Arm in. x 1.33 in. Standoff in. x 7/16 in. Aluminum Tube Nominal 3/32 in. Length 0.6 in. Bulkhead mm corner to corner Small Nylon Hinge cutting to length and pins with 0.025 in. music Hub Assembly Exploded View SCALE 4 : 5 Nose Cone Constructed using vacuum forming method. Commercially available at Apogee Components, PN # 20061. Plug foam 1 7/8 in. length be a snug fit in body tube. Gyrocopter shaft is glued inside assembly through foam plug both bulkheads. Glue nose on last. Nose Cone Assembly Exploded View SCALE 2 : 3 Plywood Bulkhead in. 5/16 in. x 5/16 in. Aluminum Tube 1/8 in. be found at the NAR/FAI website. It has been a true pleasure watching this un-named design evolve from its be- ginning. Without the interest from many of my NAR friends and U.S. teammates who like to experiment and think outside the box it would not have developed into what it is today. I eagerly wait seeing future in- novations and improvements! Making the Blades The trademark of this design is the cambered blade shape and high speed at which they spin. The blades are made from 1/32" C grain balsa with the straight trail- ing edge parallel with the grain. Soak them in a 20% ammonia to water solution until soft enough to form without cracking. Am- monia is used to solubilize plant lignin in many bio-chemical extracting processes, and has been used for many years to assist in shaping wood. My original blades were shaped on a 40mm FAI mandrel but now I use similar sized PVC and galvanized metal pipe since the blades are now longer than my original mandrel. I can also make more blades at one time. Another nice thing about using hollow pipe is that you can place a rope through its center and sus- pend it at a comfortable working height, which makes the wrapping process easier. Mark the mandrel or pipe's center- line in two or three places around it with a marker to have a guide for positioning the blades. Use masking tape to secure the ends of the wetted blades in place. I use strips of bedsheet about 3" wide to wrap the blades tightly to the mandrel. Tape one end of the cloth strip near one end of the mandrel and start the wrap on a 45° angle (see Photo 3). Secure the other end of the wrap with tape and allow sufficient time for the blades to completely dry before remov- ing. Marks in the outer surface of the balsa will be left from the wraps but will sand out with fine grit sandpaper. For sanding the upper side of the blades, support the blade on a piece of PVC pipe. Also, round all the edges. My blades are 13.5" long and 1.75" wide. At 2.125" from the root end they steadily taper to the tip where they are 3/4" wide. See the dry blades in Photo 4. Making the Hub The "Herby Hub," as Steve Humphrey coined it, uses spruce or basswood lever

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