fix(ballistics): re-fit aero coefficients against TrackMan reference capture

src/openflight/ballistics.py

@@ -44,10 +44,23 @@
 # These are simple parametric forms consistent with Bearman & Harvey (1976)
 # and Kensrud & Smith (2018) for dimpled balls past the drag crisis
 # (Re ~ 5e4–2e5), which covers the full range of realistic golf shots.
-CD_BASE = 0.205
-CD_SPIN_COEFF = 0.18
-CL_SATURATION = 0.32
-CL_HALF_SP = 0.15
+#
+# Fitted with scripts/analysis/sweep_ballistic_coeffs.py against the committed
+# TrackMan capture (session_logs/OpenFlight-Test.Normalized.csv, 24 shots,
+# differential evolution + Nelder-Mead, rho=1.184 to match TrackMan "Flat").
+# Overall carry RMSE against TrackMan: 24.52 -> 3.97 yd. The previous
+# CL_HALF_SP of 0.15 sat well above the low-spin driver regime (driver
+# Sp ~ 0.05-0.08), so for drivers the lift curve never left its low-lift
+# regime and driver carry ran ~37 yd short. Irons and wedges (Sp ~ 0.21-0.63)
+# were already past CL_HALF_SP and ran long instead, which is why the error
+# flipped sign by club. Resulting Cl is ~0.13-0.16 for drivers, rising to
+# ~0.22-0.23 for irons and wedges; the iron/wedge values sit inside the
+# 0.18-0.25 band the cited sources report, while the driver values remain
+# below it.
+CD_BASE = 0.19071
+CD_SPIN_COEFF = 0.31588
+CL_SATURATION = 0.25544
+CL_HALF_SP = 0.04758
 
 # Exponential spin decay: ω(t) = ω₀·exp(-rate·t).
 # ~4%/s per Kiratidis & Leinweber (2018); small but matters over ~6 s flights.

tests/test_ballistics.py

@@ -1,11 +1,13 @@
 """Tests for the ballistics flight simulator and launch resolution."""
 
+import math
 from datetime import datetime
 
 import pytest
 
 from openflight.ballistics import (
     CLUB_TYPICAL_SPIN_RPM,
+    SPIN_DECAY_RATE,
     LaunchConditions,
     resolve_launch,
     simulate,
@@ -136,10 +138,17 @@ def test_trajectory_ends_at_ground(self):
         assert traj.points[-1].t == pytest.approx(traj.flight_time_s, rel=0.01)
 
     def test_spin_decays_over_flight(self):
-        traj = simulate(_driver(spin_rpm=3000))
+        initial_spin = 3000
+        traj = simulate(_driver(spin_rpm=initial_spin))
         final_spin = traj.points[-1].spin_rpm
-        # 4%/s for ~6s flight → ~80% of initial
-        assert 2300 < final_spin < 2900
+
+        # Assert the decay law itself rather than a hardcoded window, so the
+        # test stays valid when aero coefficients change the flight time.
+        expected = initial_spin * math.exp(-SPIN_DECAY_RATE * traj.flight_time_s)
+        assert final_spin == pytest.approx(expected, rel=1e-3)
+
+        # Sanity: spin must fall, but not collapse over a single flight.
+        assert 0.6 * initial_spin < final_spin < initial_spin
 
     def test_flight_time_reasonable(self):
         traj = simulate(_driver())

tests/test_ballistics_trackman_regression.py

@@ -36,25 +36,24 @@
 
 TRACKMAN_CSV = _REPO_ROOT / "session_logs" / "OpenFlight-Test.Normalized.csv"
 
-# Per-club RMSE ceilings in yards, seeded from the measured baseline on
-# c9d0cc7 (2026-08-18) with a small tolerance for float/platform drift:
+# Per-club RMSE ceilings in yards. Ratcheted down after the aero coefficients
+# were re-fit against this same capture (see ballistics.py CD_/CL_ constants).
 #
-#   club              n   rmse    mae    bias
-#   7-iron            9   11.64  11.00  +11.00
-#   driver            8   38.60  37.18  -37.18
-#   pitching wedge    7   13.56  13.16  +11.02
-#   OVERALL          24   24.52  20.36   -5.05
+#                    before re-fit        after re-fit
+#   club            rmse      bias       rmse     bias
+#   7-iron         11.64   +11.00        2.96   +1.52
+#   driver         38.60   -37.18        1.75   -0.45
+#   pitching wedge 13.56   +11.02        6.26   -2.96
+#   OVERALL        24.52    -5.05        3.97   -0.45
 #
-# The driver number is large because Cl is mis-fit at low spin parameter
-# (CL_HALF_SP=0.15 sits above the driver's whole Sp range, so the lift curve
-# never leaves its low-lift regime). Fixing the aero constants should drop
-# driver RMSE substantially -- when it does, lower these ceilings.
+# Ceilings sit slightly above the measured values to absorb float/platform
+# drift. Lower them again if the model improves; never raise them.
 RMSE_BUDGET_YARDS = {
-    "driver": 40.0,
-    "7-iron": 13.0,
-    "pitching wedge": 15.0,
+    "driver": 3.0,
+    "7-iron": 4.0,
+    "pitching wedge": 7.5,
 }
-OVERALL_RMSE_BUDGET_YARDS = 26.0
+OVERALL_RMSE_BUDGET_YARDS = 5.0
 
 # The reference capture is a fixed, committed file: if the shot count changes,
 # the fixture changed and every budget above needs re-deriving.