Fig. 4. Modulation of lift with changing phase-shift between the stroke cycles of dragonfly tandem wings. (A,B) Data show modulation of forewing (A) and hindwing (B) lift averaged over the entire flapping cycles of four subsequent strokes, while phase lag systematically varied between –50% (forewing lead by a half stroke cycle) and 50% (hindwing leads by a half stroke cycle). Colors show measurements at different vertical distances between the stroke planes (1.25 to 5 mean wing chord ). (C) Phase-shift between the stroke cycles of both wings during mean peak lift changes with changing vertical distance between the two wing hinges. Black, forewing; red, hindwing; aspect ratio of the wings=2.7; flapping frequency=666 mHz; wing rotation symmetrical, starting 10% prior to and ending 10% after stroke reversal; Reynolds number=137; =4.0 cm. Data in A and B were smoothed using a numerical 3 data point adjacent averaging filter.