A study of aerodynamic drag of American footballs

American football is one of the most popular sports in North America. It is enjoyed both by participants and spectators. The centre piece of the games is the oval shaped ball. The flight trajectory of an American football largely depends on its aerodynamic characteristics. Despite the popularity of the game, it appears that scant information on the aerodynamic force experienced by an American football is available in the open literature. Although attempts were made to construct the flight trajectory of the ball, without knowing the aerodynamic drag coefficient, it is hard to build such a model. The shape of an American football is similar to that of an ellipsoid. It has more pointed ends and rough surfaces. The ball used in college level teams possesses a pair of seams at the pointed ends. This makes the airflow around the ball even more complex. The primary purpose of this study is to experimentally measure the aerodynamic forces of American footballs used at professional and college levels under a range of wind speeds and yaw angles. The non-deimensional drag coefficient were estimated 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.