Fin Sizing
How the fins geometries were determined
Before PDR
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
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
Between PDR and CDR
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
Files Used
Spreadsheet - Used for fin flutter calculations
Last updated