Fig. 4. Comparison between free and tethered flight. (A) Wing kinematics. Red, green and blue traces show the time course of stroke position, stroke deviation and angle of attack, respectively, over the course of a stroke cycle. Solid and broken lines show data from free and tethered flight, respectively. For comparison, data from a previous study using phase-reconstruction of separate stroboscopic images (Zanker, 1990a) are shown as dotted lines. Small differences of the coordinate systems used to measure wing position in this study may account for the discrepancy between the tethered flight measurements. (B) Wing motion and aerodynamic forces during free flight. For clarity, (mean) downstroke and upstroke forces are shown in blue and green, respectively. For details refer to the legend of Fig. 2B. (C) Same analysis as in B, except that data from tethered flies were used.