Fig. 2. Enhancement of mean lift coefficient for different near-clap conditions scaled to the performance of a single flapping robotic wing. The magnitude of lift coefficient C_L augmentation is 1.0 at large separation angles where the lift coefficients for one-wing and two-wing flapping are equal. Due both to the separation between the two wing hinges (gear box of the robot) and the rigidity of the model wing, the wings are closest at their tips (blue). Adding spacers at the wing hinge (red) reduces the dead space within the gap formed by the two wings during the clap. This experimental modification results in a higher aerodynamic performance at minimum angular distance between the two wings.