Much discussion surrounds the flight of a football, especially that which is perceived as irregular, and is typically done so with little understanding of the aerodynamic effects or substantive evidence of the path taken. This work establishes that for a range of FIFA-approved balls there is a significant variation in aerodynamic performance. This paper describes the methods used for mounting stationary and spinning footballs in a wind tunnel enabling accurate force data to be obtained, and the analysis techniques used. The approach has been to investigate a number of scenarios: the non-spinning Reynolds sweep, unsteady loads, orientation sensitivity (yaw sweep), and the spinning Reynolds sweep. The techniques are applied to a number of footballs with differing constructions and the results reported. To put the aerodynamic data into context, the results are applied in a flight model to predict the potential differences in the behaviour of each ball in the air. This paper concludes that, although the drag characteristics are different for each different ball tested, the simulation suggests that this has only a limited effect on the flight of the ball. It is also shown that the unsteadiness of the aerodynamic loads is unlikely to be responsible for unpredictable behaviour. However, it is also shown that there are significant differences in the lateral aerodynamic forces for a range of FIFA-approved match balls, and that these aerodynamic differences have a significant effect on the flight path for both spinning and slowly rotating balls.
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