A FRINGE SHADOW METHOD FOR MEASURING FLAPPING ANGLE AND TORSIONAL ANGLE OF A DRAGONFLY WING

A fringe shadow (FS) method was developed for measuring the frapping a ngle and torsional angle of a dragonfly wing during beating motion. Th is new method involves two sets of fringe patterns projected onto the wing from orthogonal directions. The torsional angle is determined usi ng the length of the shadow of the wing chord that is cast by the two sets of fringe patterns. The flapping angle is determined using the sh adowgraph of the wing projected by a laser. The advantages of the FS m ethod are its capability (i) to measure the flapping angle and torsion al angle of a dragonfly wing simultaneously using only one high-speed camera and (ii) to recognize the spanwise position of a section from t he number of fringes, without having to use diffuse marks that are com mon in current methods. The resolution of the FS method can be changed easily by adjusting the fringe spacing. The measurement results for t he torsional angle and flapping angle of a dragonfly wing prove the ef fectiveness of the FS method in studying the flight performance of dra gonflies.