Effect of initial attitude on autorotation flight of maple samaras (Acer palmatum)

Abstract

Many samaras or winged seeds such as maple seeds make an autorotational flight during their falling. Slow descent speed of autorotating maple seeds has been known to be caused by the high lift generated by Leading-edge vortex (LEV) on the seed blade. The autorotation flight of maple seeds is observed to be very stable after detaching from their parent plants, regardless of their initial attitude. In this study, the effects of initial attitude on the flight characteristics of autorotating maple seeds, such as descending velocity, rotational speed and coning angle were investigated experimentally. Depending on the initial attitude, the transitional flight from the initial detachment to the steady-state autorotation is clearly discernible. It starts with downward facing of the seed base, and then approaches equilibrium by changing the pitch and coning angles of the seed. The lower surface faces downward and tumbles to the downward facing state of the leading edge. Among the six initial attitudes tested, the downward facing of the seed's lower surface exhibits the fastest stabilization. Most maple seeds belong to the case of downward facing of lower surface. The present results demonstrate that the maple seeds make a stable autorotation within a distance of 660 mm after detaching from their parent plants, regardless of their initial attitude.