The wake structure trailed from samara in autorotation.

Samaras make autorotation in their falling flight from their mother tree. The descending speed during the autorotation is approximately 1 m/s but the rotational speed is widely scattered depending on their size, weight and form of the respective species. Then the strength of circulation and the structure of the trailing vortices are interesting subject in the study of the performance of autorotation. Exemplified samaras are tested in a vertical wind tunnel, visualized by a smoke line of paraffin, and filmed with the stroboscope photography.