The Aerodynamics of Spinning Seed Flight

Ruellia ciliatiflora is a perennial herb whose fruits explode and launch their thin disk-shaped seeds over 6 m with a backspin of up to 1660 Hz.

While backspin launch orientation minimizes aerodynamic drag, it is not

the range-maximizing launch orientation.

Here the three-dimensional equation of motion of a thin, spinning disk

flying through a fluid medium was derived and solved numerically to simulate

the flight of seeds of R. ciliatiflora under different launch conditions.

Simulations of seed flights reveal that the range-maximizing launch orientation

lies between sidespin and topspin, far from the backspin that is

observed in nature. The range-maximizing orientation results in a dispersal

range of nearly 10 m, but its orientation is highly sensitive to spin rate and launch angle. By contrast, backspin,

which yields moderate dispersal ranges about 60% of the range-maximizing

orientation, is robust to perturbations in launch parameters that the plant

cannot precisely control.