2-COLOR COMPENSATION METHOD FOR MEASURING UNSTEADY VERTICAL FORCE OF AN INSECT IN A WIND-TUNNEL

A two-colour compensation (TCC) method was developed for measuring the tilt angle of a gauge block generated by the beating motion of a drag onfly in a wind tunnel. in this method, a wavelength correlation was u sed to compensate the error due to beam fluctuations induced by air tu rbulence. The repeatability and resolution of the TCC method were dete rmined by using a piezo translator (PZT) to generate the tilt angle va riation. The results show that by using the TCC method the error in ti lt angle measurement due to air turbulence can be decreased by about 5 0% compared with that using a one-wavelength method. The TCC method wa s then applied to measure the tilt angle variation caused by the beati ng motion of a dragonfly attached to one end of a gauge block in a win d tunnel for a wind velocity of 4 m s(-1). The results confirmed the e ffectiveness of this new method.