Drag Crisis of Gyro-Balls

Using a high-speed video camera, we measured the trajectory and the rotation of a hard baseball thrown by a pitching machine which can launch Gyro-Balls (rifle spinning balls). We determined the drag- and lift- coefficients by analyzing the video images. The measurements were performed in the range of 0.6$\times $10$^{5}<$Re$<$2.5$\times $10$^{5}$, and for three values of the spin parameter (SP : dimensionless spin rate)=0.12,0.23 and 0.35. Two seam patterns relative to the translational direction were investigated, i.e. 2-seam and 4-seam. The drag coefficient of a 4-seam gyro-ball with SP=0.12,0.23 and 0.35, decreases gradually with Re. However, the drag coefficient of a 2-seam gyro-ball with SP=0.12 decreases in two steps, i.e. in the ranges 0.8$\times $10$^{5}<$Re$<$1.0$\times $10$^{5}$ and 2.0$\times $10$^{5}<$Re$<$2.2$\times $10$^{5}$, and attains its minimum at Re=2.2$\times $10$^{5}$. The drag coefficients of a 2-seam Gyro-Ball with SP=0.23,0.35 are almost constant below Re=1.6$\times $10$^{5 }$and Re=1.3$\times $10$^{5}$, respectively. Their minima are attained at Re=1.8$\times $10$^{5}$ and Re=1.6$\times $10$^{5}$, respectively. These findings confirm the occurrence of the drag crisis for Gyro-Balls. The different Re-dependencies are due to the different seam patterns.