Sport Rocketry

A and B Payload Design for 13mm Motors by Dan Wolf On page 9 is a plan for A and B engine class Payload rockets. "Payload" is an NAR contest event where the rocket must contain a 17.5mm diameter cylinder (fits inside an 18mm/aka BT-20 body tube) that is between 60mm and 70mm long that contains sand (the payload). The weight of the cylinder must be at least 28 grams. It is an altitude event. Altitude events are usually flown using al- timeters, so the rocket must carry an altimeter also. The portion of the rocket carrying the payload must be returned. Typically the payload is then weighed to verify the weight is at least 28 grams. A and B engine payload events are contest events that can be NRC (National Rocketry Championship) events. Each year, the NAR Contest Board selects six of the so-called NRC events to be flown all year long at NRC launches. Altitudes from those flights appear on the NAR National Scoreboard on the NAR website. Besides Payload, the other NRC events are parachute duration, streamer duration, boost glider duration, helicopter duration, egg- loft duration, and eggloft altitude in different engine size classes. See the U.S. Model Rocket Sporting Code for more details. When writing up the B Payload event coverage for Sport Rocketry, I was surprised that a 13mm motor two-stage payload (B payload) plan or a single 13mm motor payload plan (A payload) had never been published. I started looking after I observed that the winning flights in A, C, and D divisions were made with two- stage 13mm motor powered models. One of those was the Apogee Rocket's Midge design flown by A division winner Ashley Van Mil- ligan. The other two were scratch built designs. My scratch built payloader was similar to those, and with the event being flown at NARAM again this year I felt it was time a plan should be pub- lished. For A Payload, a single 13mm Estes A3-4T is used. For B Pay- load, a booster stage is added that uses the Estes A10-0T. While B Payload can be flown using 18mm motors, the lower base drag and lower mass of the two-stage 13mm design typically flies higher than black powder B motor powered designs. However, with the advent of the Quest B4-6, which has more total impulse than the A10-0/A3-4T combination, the advantage is not as clear cut. How- ever, at NARAM-61, the best flights were made with the staged 13mm rockets. You mileage, er, altitude, may vary. Assembly 1. To build this rocket, first start with a 115mm (4.5") length of 13mm body tube. I used Balsa Machining Service T5. After cutting the tube to length, wick some thin Cyanoacrylate glue into the ends to strengthen the tube and to keep the tube ends from fraying when sanding. Sand off any that gets inside the tube. After that, sand the tube smooth starting with 220 grit sandpaper, then 320 grit, 400, 600, 1000, and even 1500. I find I can get a very smooth finish on the BMS tubing this way. The spiral seam could also be filled with thin CA or wood filler, but I don't usually bother. A longer tube is okay if you can't fit the recovery system. I am just able to fit an 8" chute in this tube, but it is a tight fit. 2. Next cut the fins from 10 mil G10 fiberglass. If building the two-stage B class rocket, cut six fins, three for the upper stage and three for the booster. Sand the fins smooth with progressively finer sandpaper as was done for the body tube. Also sand and round the 8 JANUARY/FEBRUARY 2020 SPORT ROCKETRY Quickly Locate Your Downed Rocket in MINUTES! Powerful Tracking Transmitters 2-9 Mile Ground Tracking Range/10+ Mile Air Tracking Range Lightweight Transmitters 2 Grams & up Waterproof Circuits Durable and Easily Transferred from Rocket to Rocket Telemetry Specialists Since 1970 Receiver Models Tracking from 3 to 200 Rockets Formerly Walston Retrieval TRACK YOUR ROCKET FROM LIFT OFF TO LANDING! 1202 Walnut Street Murphysboro, IL 62966 800-842-4537 Toll Free www.wmimodelaeronautics.com 618-687-3505 Fax: 618-687-3539 Email: mikec@caretrak.com Continued on page 14.

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