Expectations vs. Reality The Banshee

1. Expectations vs. Reality The Banshee

2. Flight Data Motor – J800T, 1280ns Total Impulse, 1.9 sec burn time Apogee – 2754 feet @ 12.95 seconds Main – 697 feet @ 51.4 seconds Touchdown – 73.7 seconds

3. Other Example Altimeter Readings

4. Simulation vs. Reality

5. Diameter Discrepancy • Public Missiles Phenolic Airframe Tubing Spec – 3.962” • Public Missiles Pre-Glassed Phenolic Airframe Tubing Spec – 3.995” • As used – PML Phenolic Airframe Tubing w/2 layers of Giant Leap “fiberglass sock” – measured at 4.25” (after flight) • Fin can also has an additional 2oz layer of fiberglass

6. Lift Off Weight Discrepancy • Design 10.6 lbs • Weights defaulted from Rocksim • I Assumed 8z for paint and epoxy • Actual 17.7 lbs • Slightly underestimated several components • Considerably underestimated paint and epoxy • Fiberglassing not in original estimate, probably about 3 lbs • Aprox 1 lb of epoxy + foam • Easily 15 cans of primer and paint used…

7. Peak Altitude Discrepancy • Initial Design – 5426 Feet • Lower weight • 4” diameter smooth profile • Wind estimated 8-14mph • .5” motor overhang • Constructed – 3147 Feet • Correct weight • 4” diameter smooth profile assumed • Wind estimated 8-14mph • .5” motor overhang • Post Op – 2754 feet actual, ran simulation again – result of 2817 feet • Correct weight • 4.25” diameter – turbulent transition from nose cone • Actual wind – upper end (14+mph) – more weather cocking • .5” motor RESESS – CG forward – more weather cocking • Launch rod tilted 5deg into the wind (est. from photos)

8. Landing Velocity Discrepancy • 9’ home-made parabolic cupped design • Design from Rocket Team Vatsaas (http://vatsaas.org/rtv/) • Assumed cD of 1.5 (from their website) • Should have brought down 18 lb rocket at 19fps • Richard Nakka’s Experimental Rocketry website has a detailed dissertation on parachutes, suggesting a more reasonable cD of .6 • A cD of .6 on an 18 lb rocket results in 29fps, which matches my result