Aerodynamic drag measurement of American footballs

The flight trajectory of an American football largely depends on its aerodynamic characteristics. Despite the popularity of the game, it appears that little information on the aerodynamic force experienced by an American football, especially under crosswinds is available in the open literature. The shape of an American football is similar to that of an ellipsoid. It has more pointed ends and has a rough surface. The ball used in college level teams possesses a pair of seams at each of pointed ends. All these features and crosswind make the airflow around the ball more complex. The primary purpose of this study is to experimentally measure the aerodynamic forces of professional (NFL) and College levels (NCAA) American footballs under a range of wind speeds and yaw angles. The non-dimensional drag coefficients were determined and compared. The results indicate that the American footballs possess drag coefficient close to that of other oval shaped balls such as Rugby and Australian rule footballs. It also shows that the drag coefficient can be almost four times higher under crosswinds.