Sport Rocketry

in Figure 12. I paid particular attention to design of the lower assembly. This relatively stubby assem- bly (20" tall) had to support the thrust of an AeroTech J570 motor while simultaneously re- sisting the crushing downward force of a 2,241-gram lander. The rocket flight simulations showed that the launch vehi- cle would accelerate upward at 128.45 meters/sec 2 . If you divide that acceleration value by the g value of 9.8 m/s 2 , you get 13.1 G's. There is also the weight of the lander that is being supported by the deck (until the lander and airframe are in free fall), so the force on the deck from the lander will equal 14.1 times the weight of the lander. And 14.1 times the weight of the 2.241 kg lander would be: 2.241 * 9.8 * 14.1 = 309.7 newtons (which is al- most 70 pounds of force). Considering the forces the lander mass would exert on this deck during launch, I heavily reinforced it, sand- wiching it between internal body stiffeners at top and bot- tom. The internal stiffener extended down from the un- derside of the lander deck cen- tering ring to the top side of the top motor mount center- ing ring, effectively creating a SPORT ROCKETRY MAY/JUNE 2017 27 Mid and High Power Rocket Motors Delivered to Your Doorstep E through M Motors in Stock ✔ Real Time Inventory ✔ Same/Next Day Shipping ✔ Order Confirmation ✔ Order Tracking ✔ No Memberships ✔ Shipping to Alaska please inquire Proud Supporter of TARC highly reinforced area. Additional centering rings were used to sandwich the through-the-wall fin mounts top and bot- tom; again, the goal being to create a very structurally sound lower assembly that would not crumple like an empty soda can under launch load. The upper airframe assembly also used reinforced cen- tering rings and was split into two internal sections. Flight systems resided in a custom recessed electronics bay that was secured into the low- er section of the upper as- sembly. The electronics bay was constructed with mixed-media: 3D printed and cardboard. I utilized dual Featherweight Raven 3 flight systems and dual RC battery packs for redun- dancy. The vehicle recovery chutes, cords, and pyros resided in the upper sec- tion of the upper airframe assembly with a downward facing 1080p DVR mounted externally. Finally, a fiber- glass "bull-nose" nosecone topped off the upper assem- bly. She utilizes two 1515 rail buttons attached to 3D printed extenders. Fully as- sembled and loaded Mestler launch vehicle stood 62" tall with a launch configuration weight of 7,993 grams. Figure 13 shows three still frames from a pyro test con- ducted to be sure the two halves of the payload bay would separate as designed. Figure 13. A pyro test was performed to be sure the two halves of the payload bay would eject as designed. Success!

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