A-32 Negative Magnus Force Exerted on a Back-spinning Spherical Body : Measurement by Flight Experiments

Using a high-speed video camera, we measured the trajectory and the rotation of a sphere and a hard baseball thrown by a pitching machine. We determined the drag- and lift- coefficients (C_D, C_<LZ>) by analyzing the video images. The measurements were performed in the range of 0.6 × 10^5 <Re< 2.4 × 10^5, and 0<SP<0.7 (SP : dimensionless spin rate). The dependence of C_D and C_<LZ>on the parameters Re and SP is investigated in detail. Negative Magnus force is exerted on a back-spinning sphere in a relatively wide Re- SP parameter range, whereas only usual Magnus force works on a back-spinning hard baseball. The influence of seam patterns on the aerodynamical properties is discussed.