Instantaneous Aerodynamic Forces Developed by an Indian Moon Moth, Actias selene, in Near-Hovering Flight

Abstract

The slow-climbing free flight of a 3.36-g female Indian moon moth, Actias selene, was recorded with a cine camera. The mean stroke plane was at 13.4° to the horizontal, and the stroke angle was close to 180°; the wingbeat frequency was 14.5 Hz. A semiconductor strain-gage probe was used to measure the instantaneous forces on the thorax of a 1.84-g male moth beating its wings in tethered flight. The wingbeat frequency of the tethered moth was 9.15 Hz, and the tethered moth produced a mean aerodynamic force only two-thirds of its body weight. The mid-downstroke instantaneous lift (2.93) and drag (2.14) coefficients of the tethered moth were larger than is consistent with quasi-steady-state aerodynamics. The possible causes of these high force coefficients are discussed. The aerodynamic power output, calculated from the instantaneous aerodynamic drag force, is 1.45 W/N of body weight. Published estimates for Lepidoptera are 0.6-0.9 W/N.