Fig. 7. Force comparison between experiment, computation and quasi-steady predictions for (A,D) advanced (=/4), (B,E) symmetric (=0) and (C,F) delayed (=–/4) rotations. (A–C) Force traces of four strokes starting from rest. Red, experimental force; blue, computational force; green, quasi-steady estimates using Equations 14, 15, 16, 17. Forces are normalized as in Figs 2, 3, 4. (D–F) Difference trace (red) between the experimental forces and quasi-steady forces. Linear acceleration du(t)/dt (blue), and an estimate of rotational force u(t)(t) (green) are shown in arbitrary scale since we are only interested in their basic time course. Broken vertical lines mark the wing reversal during t=[1,2]. Features associated with rotation (r) and unsteady circulation due to wing acceleration (u), are labelled accordingly.