Fig. 1. Schematic reconstruction of wake pattern during wake–wing interaction in fruit fly and dragonfly model wings. (A–D) Wake capture mechanism at dorsal and ventral stroke reversal. At the beginning of each half stroke, the leading and trailing edge vortex system generates an inter-vortex stream towards the wing. (E–H) Schematic reconstruction of vortex generation and shedding during clap-and-fling maneuver using a generic Drosophila stroke kinematics (Lehmann et al., 2005). Chordwise wing segments at the end of the upstroke (F), during the clap phase (G), and during the fling phase (H) before the two wings separate for the downstroke. Leading and trailing edge vortices are shed into the wake at the end of each half stroke. The low-pressure region evolving between the wings during the fling pulls fluid around the leading and the trailing wing edge into the opening cleft. (I–K) Reconstruction of vortices and local flow conditions at maximum transient lift production in tandem model wings of a dragonfly. (I) Wing kinematics follows a generic pattern, as found in various species (Maybury and Lehmann, 2004). (J,K) Flow characteristics at 0.35 fraction of the stroke cycle at which either the fore- (upper wing; J) or the hindwing (lower wing; K) leads wing motion by a quarter stroke cycle. Local flow vector (black) in the vector diagrams is calculated from the velocity and angle of the combined fore–hindwing downwash (green vector) determined in a region below the hindwing's surface and the translational velocity of the hind wing section (gray vector). Effective angle of attack for the hind wing section (left value) and local flow velocity (right value) are shown, respectively, in parentheses below the vector diagram. Open arrows indicate the direction of wing motion. Vortical circulation in the hindwing's leading edge vortex (LEV) is shown in parentheses. The different strengths of starting and leading edge vortices are indicated approximately by the size of the plotted vortices. Blue and red arrows represent normalized vectors of total force attenuation and enhancement, respectively, compared to a wing flapping free from mirror- (F–H) and forewing (J,K) downwash. The exact inclination of the force vectors slightly differs from the orientation normal to the wing's surface, as shown in the schematics, because of shear forces in the fluid.