Fig. 9. Schematic reconstruction of wake pattern during wing–wake interaction in fruit fly model wings and effect of heaving motion during clap-and-fling. (A,B) The graphs show chordwise wing segments during clap-and-fling at the end of the upstroke, during the clap, and during the fling phase before the two wings separate for the downstroke. 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. Inflow of fluid during fling potentially increases during heaving down motion, as shown in A, and decreases when the wings move upwards at the beginning of the downstroke, as shown in B (cf. length of black straight arrows). (C) Simplified hypothetical analytical simulation modelling the inflow velocity between both leading wing edges during fling. Angular velocity during dorsal wing rotation and wing size are taken from a tethered flying fruit fly. The model predicts a reduction in flow velocities into the opening cleft during upward heaving motion whereas flow velocity increases during downward heaving compared to a wing beat without heaving motion (blue). (D) Heaving rate and direction plotted against vertical force augmentation during clap-and-fling wing beat. Pictogram illustrates the change in stroke angle (, black), the wing's angle of attack (_m, blue) and heaving angle (, green). Heaving rate was derived from the angular change within a time window of 0.1 stroke cycle after the wing has started the downstroke. (E) Effect of heaving up and down motion during fling on vertical force coefficient of a single wing (left), absolute vertical force augmentation when flapping both wings (middle) and relative vertical force augmentation due to clap-and-fling (right). NS, not significant; ***P<0.001 significance level.