Aerodynamic effects play an important part in any sport where the ball experiences significant periods of free flight. This article investigates the aerodynamic forces generated when a football is spinning quickly to generate swerve and more slowly to generate more erratic flight. The work reports on the application of an experimental method that measures the aerodynamic loads on a non-spinning, slowly spinning and fast spinning football, using a phase-locked technique so that orientation-dependent and steady ‘Magnus’ forces can both be determined. The results demonstrate that the orientation-dependent aerodynamic loads, widely seen in non-spinning data in the literature, surprisingly persist up to the highest spin rates reported. When predicting ball flight, it is generally assumed that at low spin rates a quasi-static assumption is acceptable, whereby forces measured on a non-spinning ball, as a function of ball orientation, apply for the spinning case. Above an arbitrary spin rate, the quasi-static assumption is replaced with the assumption of a steady ‘Magnus’ force that is a function of spin rate and ball speed. Using a flight model, the quasi-static assumption is shown to be only applicable for the lowest spin rates tested and the assumption of a steady ‘Magnus’ force is only applicable at the highest spin rates. In the intermediate spin rates (20–40 r/min), the persistence of the orientation effects is shown to have sufficient effect on the flight to be an important additional consideration.
The game of football is world's most viewed, played and loved sport. Due to increasing technological advancements and demand for performance, the ball manufacturers have been developing new designs progressively since its inception over 100 years ago. A traditional spherical football made of 32 leather panels stitched together in 1970s has become 14 synthetic curved panels thermally bonded without stitches in 2006 and more recently 8 panels thermally bonded in 2010, and again some new designed balls in 2013. Despite being most popular game in the world, no data is available on aerodynamic properties of recently FIFA approved Adidas Cafusa (thermally bonded 32 panels), Nike Maxim (stitched 32 panels), Umbro Neo 2 Pro (stitched 14 panels, and MitreUltimax (stitched 26 panels) footballs. Hence the primary objectives of this study are to evaluate aerodynamic performance of these recently introduced balls and compare their aerodynamic properties. The aerodynamic forces and moments are measured experimentally for a range of wind speeds in wind tunnel. A field trial using professional players has also been undertaken. The aerodynamic forces and their non-dimensional coefficients were determined and compared. The player's perception was also discussed.