Fig. 8. Vorticity contours near the hindwing with superimposed velocity vectors at 35% of stroke cycle when hindwing lift is enhanced or attenuated maximally (^*2 in Fig. 4). Vorticity and velocity vectors for the kinematic condition in which (A) hindwing lift is attenuated maximally (worst condition; forewing leads by a quarter stroke cycle), and (B) hindwing lift exceeds lift production of a single hindwing flapping free of forewing downwash interference (best kinematic pattern; hindwing leads by a quarter stroke cycle). Square white boxes indicate the regions from which circulation of the leading edge vortex was measured. The wing sections (white lines) are viewed at 50% distance between the wing base and tip, and have a geometric angle of attack of 45°. The direction of wing translation is from left to right. T, stroke cycle.