The Kinematics of Falling Pterocymbium Tinctorium Seeds

Abstract

Pterocymbium tinctorium (Thai:ปออีเก้ง, Por-Ae-Keang ) is a tree found in Thailand and other Southeast Asian countries. The fruit, containing a single seed with an attached single wing extending to one side and a hollow boat-shaped structure that braces the wing in flight, is known as a samara. The vertical terminal velocity and spin frequency of the falling samara were studied for a representative sample of the population. The effect of mass on terminal velocity and spin frequency was then investigated for a single typical seed. The motion was recorded with a high-speed camera. The terminal velocity and spin rate were determined and the coefficient of lift was estimated. In the population study, no significant correlation was found between seed mass, wing area, terminal velocity, and frequency. It is concluded that parameters such as angle of attack or wing curvature are likely have a larger impact on the aerodynamics. As the mass of one selected seed was increased, terminal velocity, frequency, and lift force also increased, following the trend found elsewhere for Dipterocarpus Alatus samaras. It was shown that 80-90% of the vertical retarding force generated during the fall was from lift and that the coefficient of lift for the seed used was close to constant, varying between about 0.3 and 0.4.

Keywords

• pterocymbium tinctorium
• winged seed
• mass
• population variability
• terminal velocity
• aerodynamic lift