Empirical fin-flutter screening¶

The tool implements the corrected Bennett (2023) presentation of NACA TN 4197 equation 18, also used in the Rocketry Forum calculator. This is a preliminary structural screen, not a full aeroelastic analysis.

\[ V_f=a\sqrt{\frac{2G(t/c_r)^3(AR+2)}{1.337 AR^3(\lambda+1)P}},\qquad AR=\frac{s^2}{s(c_r+c_t)/2},\quad\lambda=\frac{c_t}{c_r}. \]

s is exposed fin semispan; c_r, c_t are root and tip chords; t is thickness; G is effective shear modulus; P is atmospheric pressure; a is local sound speed. The flight-exposure ratio is actual air-relative speed / estimated flutter speed. Values closer to or above 1 indicate greater exposure under this empirical model.

Set up in the UI¶

On the Optimization tab, find Empirical fin-flutter screening. To enable enforcement, check Enforce explicitly configured screening constraint and enter Effective shear modulus (GPa) plus Maximum flight-speed / estimated-flutter-speed ratio. Both fields are blank by default. The threshold is user-selected; there is no universal setting supplied by the program.

In Candidate Details, the Flutter screening tab can calculate from a saved flight and open Flutter boundary plot..., comparing modeled speed with the empirical boundary along ascent.

How to interpret¶

The implementation checks ascent samples using candidate-specific geometry and atmospheric state. Material shear modulus is highly consequential; a single effective modulus for composite fins is an approximation. The model does not resolve composite ply structure, root attachment compliance, manufacturing variation, or a detailed coupled aeroelastic response. Do not call a candidate certified safe merely because its ratio is below a selected threshold.

Verified example versus actual Sorcerer material¶

The Assignment 14 demonstration used G = 3.0 GPa and maximum exposure ratio 0.65, explicitly as assumptions. All six evaluated candidates passed the flutter screen. These values should not be copied as measured material inputs for a new Sorcerer configuration.

Original references¶

Source basis: Assignment 14 review materials supplied with this documentation. Internal archive paths and raw evidence are not published.