223 A Study of Butterfly Flight by Measuring a Flight of a Tailless Ornithopter
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A butterfly-type ornithopter (BTO) was developed to investigate flapping flight of butterflies. The BTO has the same values of wing length, flapping frequency and wing loading as butterflies. It flew forward when its center of gravity was appropriate. Its longitudinal motion was measured with a high-speed video camera. We found that the angle of attack of the body axis, α_<body>, varied coincidentally with flapping motion. Periodical change of α_<body> in the flight of a real butterfly was also observed. To reveal the effect of the change of abody on the aerodynamics, we visualized the flow around the BTO both in tethered flight and in free flight. In tethered flights, leading edge vortex was attached to the wing during downstroke when α_<body> was 20°, but it separated from the wing when α_<body> was 40°. However, in a free flight, leading edge vortex was attached to the wing in spite of the large value of α_<body>, 50°, in the beginning of downstroke.
