Mechanism of autorotation flight of maple samaras (Acer palmatum)

Abstract

Some winged seeds exhibit autorotation flight during their descent to migrate far away from their parent trees by using oncoming wind. The reduced descent speed of autorotating maple seeds is attributed to the high lift force generated by a leading-edge vortex (LEV). In this study, several prominent features of the autorotation flight of maple samaras (Acer palmatum) were investigated experimentally. The autorotation flight of each maple seed was observed to be very stable during its fall. The nominal values of the dynamic motion parameters were 1.2 m/s for descent velocity, 130.9 rad/s for spinning rate, 22 degrees for coning angle, and 1.5 degrees for pitch angle. Velocity fields of the flow around an autorotating maple samaras model were measured by particle image velocimetry; wind speed was controlled to be similar to the descending velocity. As a result, a highly stable LEV was attached on the leeward side of the autorotating seed.