Fig. 8. Estimates of circulation of leading edge vortex (LEV) during dorsal stroke reversal in the robot while flapping its wings as shown in Fig. 1A–D. (A–E) LEV circulation measured at five different distances from the wing base. Pictograms illustrate wing shape and the yellow layer in each pictogram indicates the DPIV layer that was used for the analysis. LEV circulation for a single wing flapping is shown in red; when flapping two wings, in blue. (F) LEV circulation throughout the clap-and-fling maneuver and averaged over all five DPIV layers (cf. Materials and methods). Green data show the difference between both flapping conditions and demonstrate how LEV vorticity increases due to wing–wake interference during clap-and-fling.