Fig. 5. Phase-shift induced modulation of mean lift production depends on wing length in tandem model wings. The length of the model wings was 6.9 (light gray), 7.7 (blue), 8.5 (purple), 9.3 (orange), 10.1 (black), 10.9 (red), 11.7 (green) and 12.5 cm (dark gray). (A) Lift modulation of the lower hindwing (12.5 cm wing length), while length of the upper forewing varied between 6.9 and 12.5 cm. (B) Lift modulation in length-changing forewing and length constant hindwing of 12.5 cm. (C) Combined fore- and hindwing lift as shown in A and B, respectively. (D) Hindwing lift modulation during length changes of the hindwing. Forewing length is constant at 12.5 cm. (E) Peak phase at which fore- (black) and hindwing (red) produce maximum mean lift. Data are plotted against the ratio between hind- and forewing length. A value of 1.0 means that both wings have equal length (12.5 cm). (F) Strength of peak-to-peak modulation of fore- (black) and hindwing (red) lift production. Modulations were derived from sinusoidal fits to the data set (forewing lift: fit on data between ±15% phase-shift, hindwing lift: fit on all data) as shown by the colors in A–D. Insets in E show the shape of the model wings used in the experiments. The rounded wing tip was similar in all wings while total wing length varied between minimum and maximum values. Aspect ratio varied between approximately 1.7 (6.9 cm wing length) and 3.1 (12.5 cm wing length), respectively. Wing chord=4.0 cm. Vertical distance between both wings was 1.25 mean wing chord. For kinematic pattern, see legend of Fig. 4. More information on the methods is given elsewhere (Maybury and Lehmann, 2004).