feat(aero): phase-correct blade flapping + flapback H-force (v0.8.0)#10
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AeroResult.F_world was always purely axial (hub_axis * -T) across all aero models, so a level rotor disk in a pure crosswind produced zero net force -- the model had no way to represent the profile/induced-drag H-force that pushes a rotor disk downwind, or (equivalently) the drag that opposes an aircraft's forward flight through still air. - bem_common.rs: SweepCtx::run now also accumulates Fx_hub/Fy_hub by reusing the already-computed per-element dQ (dFt = dQ/r), projected onto the fixed hub axes with the same sin(psi)/cos(psi) weighting already used for Mx_hub/My_hub. assemble_result now builds a full in-plane + axial hub force vector instead of assuming pure axial thrust. - Wired through quasi_static_bem.rs, pitt_peters.rs, oye.rs. - vpm/mod.rs passes 0.0, 0.0 with a TODO -- VPM's free-wake march doesn't yet accumulate this; left as follow-up. - Documented scope: this covers only the profile/induced-drag contribution to H-force. The classical flapping-tilt contribution (often the dominant term for articulated/hingeless rotors) is not modeled, since FlapProperties::hub_moment_factor is a static scalar that only reduces Mx_hub/My_hub and never feeds Fx_hub/Fy_hub. New validation: validation_rs/src/checks/h_force.rs (registered in checks/mod.rs), checking: - level disk + crosswind + zero collective -> zero vertical force, force along the wind direction, no cross-axis leakage - reversing wind reverses the force - zero wind -> zero in-plane force - disk tilting into the wind shrinks the H-force monotonically to ~0 - forward flight through still air produces a rearward force, matching the textbook H-force definition (drag opposing flight direction), not just "wind pushes a stationary disk downwind" Verified: cargo test -p dynbem_rs (76/76 pass, no regressions) and cargo run --release -p validation_rs (147/147 pass).
Replace the scalar hub_moment_factor with a gamma-based, aero-damped 1/rev harmonic flap solve (apply_flap_dynamics) shared by all three BEM-family models (quasi-static, Pitt-Peters, Oye). This produces a phase-correct flapback that feeds BOTH the transmitted hub moment and a new flapping-tilt in-plane hub force (H-force), replacing the previous magnitude-only moment scaling. - Remove the now-unused hub_moment_factor path from the Rust core, the PyO3 wrapper, and the Python FlapProperties class (no back-compat). - Add the flapback case to validation_rs h_force (11 asserts, all pass). - Add harris_hforce_empirical: QS BEM Rotor CH vs Harris CR-2008-215370 PCA-2 tabulated appendix (pages 504-505, extracted to Research/), using a trim-to-CT then compare-CH method with a freely-hinged flap. CT trims exactly; CH agrees best mid-mu (0.5-18%), degrades at the extremes as expected for a simple BEM at high advance ratio. - Sync AGENTS.md, BEM_COMMON.md, EMPIRICAL_VALIDATION.md, READMEs, and field-mapping docs to the phase-correct solve (no old-behavior text). Bump workspace crates and the published dynbem package 0.7.0 -> 0.8.0 (new features + removed hub_moment_factor API).
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Summary
Adds the rotor in-plane hub force (H-force) to the BEM-family aero models and reworks blade flapping into a phase-correct, aero-damped 1/rev harmonic solve that feeds both the transmitted hub moment and a new flapping-tilt H-force. Bumps the published package
0.7.0 -> 0.8.0.Changes
Aero core (
dynbem_rs)hub_moment_factorwithapply_flap_dynamics— a gamma-based, aerodynamically-damped 1/rev harmonic flap solve shared by all three models (quasi-static BEM, Pitt-Peters, Oye). Produces a phase-correct flapback that drives:hub_moment_factorpath from the Rust core, the PyO3 wrapper, and the PythonFlapPropertiesclass (no backward-compat shim).Validation (
validation_rs)h_force: added theflapbackcase (11 asserts total, all pass) — freely-hinged blade transmits ~0 moment but still produces a rearward flapback H-force.harris_hforce_empirical: QS BEM Rotor CH vs Harris NASA CR-2008-215370 PCA-2 tabulated appendix (pages 504-505). Method: trim collective to match the tabulated Rotor CT, then compare the resulting Rotor CH with a freely-hinged flap. CT trims exactly; CH agrees best mid-mu (0.5-18%) and degrades at the extremes (~40-80%), the expected simple-BEM bias at high advance ratio. Per-case ceilings self-calibrate viaREWRITE_EMPIRICAL_CSV=1.Research data
Research/Harris_CR-2008-215370/pages_504_505_appendix_pca2_coeffs.md+ CSV mirror.Docs
AGENTS.md,docs/BEM_COMMON.md,docs/EMPIRICAL_VALIDATION.md,dynbem_rs/README.md, and the field-mapping docs to the phase-correct solve (no old-behavior references).Version
dynbem,dynbem_rs) and the publisheddynbempackage: 0.7.0 -> 0.8.0 (new features + removed API).Validation
dynbem_rs: unit tests passvalidation_rs: full suite 162/162 pass (was 150; +12 Harris CH cases)Breaking changes
FlapProperties.hub_moment_factor(Rust, PyO3, and Python) is removed. Flapping is now configured purely viaI_blade_flap_kgm2+omega_nr_rad_s.