Fig. 1. The model wing and the flapping motions. (A) Left: spatial configuration of the flapping motion of the model wing. oxyz, the wing-fixed frame (y-axis vertical to the ground); D and U, the translational extreme positions; R, model wing length; r, effective model wing length; , stroke amplitude; (t), instantaneous translational angle. The thick black line denotes the leading edge. Right: the motion of a section of the wing. (t), instantaneous angle of attack; (t), instantaneous rotational angle [(t)=90–(t)°]. The black thick line denotes wing section and the solid-dot the leading edge. (B) The kinematic curves in one period. The translational and rotational angular positions are normalized using and _M (the maximal rotational angle), respectively. The black lines at t/T=0.125, 0.25 and 0.375 denote the DSPIV measurement phases.