Fig. 1. Wing motion and force production of a robotic wing performing a clap-and-fling kinematic maneuver. (A–D) Diagrams of wing motion indicating magnitude and orientation of total force vector measured by a force transducer during the downstroke (red) and upstroke (green) of a dynamically scaled robotic model wing (stroke amplitude=160°; cycling frequency=0.16 Hz; geometrical angle of attack at midstroke=45°; wing shape similar to a Drosophila wing; mean Reynolds number is 134 and typical to Drosophila wing motion). Small circles at the beginning of each wing section (blue line) indicate the leading edge of the moving wing. The kinematic pattern was derived from kinematic data published for a tethered flying fruit fly Drosophila (Zanker, 1990a). The performance of flapping a single wing is shown in A and B. The vectors in C and D demonstrate forces produced by the wing when simultaneously flapping an imaged wing in close distance to promote the clap-and-fling maneuver at dorsal reversal. (E) Relative augmentation of the mean force vector coefficient due to the clap-and-fling wing beat, scaled to the performance of a single wing flapping. Data are plotted as a function of the angular distance between the two wing hinges. The pictogram illustrates the position of the wing's leading edge (blue line) during the clap and the location of the two robotic wing hinges (view normal to the stroke plane). To avoid direct mechanical stress on the force transducer, the wing tips do not physically touch during the clap phase. (F) Alterations of the mean force vector inclination with respect to the horizontal stroke plane when varying the angular distance between the two wings during the clap-and-fling maneuver. An angle of inclination greater than 90° indicates that the force vector points slightly into a ventral direction, which results in a pitching (nose) down moment. (G) The ratio between mean lift and drag coefficients (averaged over the entire stroke cycle) demonstrates how aerodynamic efficacy changes with decreasing angular distance of wing separation during dorsal stroke reversal.