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How the fins geometries were determined |
- Material Choice: Fiberglass (Balsa wood too weak given geometry and speed)
- Geometry Options
- Best Performance: Triangular
- Root chord: 8 in.
- Tip chord: 0 in.
- Height: 5.5 in.
- Max rocket speed is 92% max fin flutter speed
- Highest apogee: 8460 ft.
- Best Choice: Trapezoidal
- Root chord: 8 in.
- Tip chord: 3 in.
- Height: 5.2 in.
- Max rocket speed is 65% max fin flutter speed
- Highest apogee: 8344 ft.
- Viable: Elliptical
- Root chord: 8 in.
- Height: 5.2 in.
- Highest apogee: 8282 ft - consistently outperformed by trapezoidal fins with comparable stability, geometry
- Best Performance: Triangular
- Thickness Choice: 1/8” (Thinnest option that could withstand max speeds)
- Stability
- Ranges from 1.31 - 1.5 on design view
- Consideration of high speeds shift this stability to around 1.8-1.9 according to simulations, so this meets the recommended requirements
- For lower stage fins, a range of 1.5 - 2.5 should be used, which of course means a change of geometry
- Decided on trapezoidal over elliptical based on OpenRocket data
- Increased thickness of both sets of fins to 3/16” based on FinSim data because FinSim accounts for fin divergence also
- Adjusted the geometries based on the most recent (version 2.0.1) ork to work with stability margins and updated to version 2.0.2 (All ork versions)
- Upper Stage
- Root Chord: 8”
- Tip Chord: 3”
- Height: 5.5”
- Stability: 1.27 cal
- Lower Stage
- Root Chord: 10”
- Tip Chord: 3.5”
- Height: 5.7”
- Stability: 2.19 cal
- Upper Stage
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Spreadsheet - Used for fin flutter calculations