Lift crisis of a spinning table tennis ball

The aerodynamic properties of a spinning table tennis ball were investigated using flight experiments. Using high-speed video cameras, the trajectory and rotation of an official ball (Nittaku 3-Star Premium), which was launched by a three rotor machine, were recorded. The drag and lift coefficients ( C _D and C _L) were determined by analysing the video images. The measurements covered the speed and rotation range of typical table tennis shots in the form of the Reynolds number ( Re ) and dimensionless spin rate ( SP ), i.e. 3.0 × 10⁴ <  Re  < 9.0 × 10⁴ and 0 <  SP  < 1.0, and C _D and C _L were obtained as functions of Re and SP . We determined that the lift coefficient C _L is not a monotonically increasing function of SP . A deep valley of C _L was found around SP  = 0.5, and the lift force exerted on a spinning ball almost vanished at Re  = 9.0 × 10⁴ and 0.48 <  SP  < 0.5. These results qualitatively agree with the results from recent wind tunnel tests, but quantitative differences owing to the unsteady nature of the flight experiments remain. This anomaly in the lift coefficient should be called the 'lift crisis'. (paper)