Newswise – Tsukuba, Japan – Scientists from the University of Tsukuba’s Faculty of Health and Sports Sciences have used aerodynamic experiments to empirically test the flight properties of a new four-panel soccer ball adopted by the English Premier League this year. Based on projectile and wind tunnel data, they calculated drag and lateral forces and found that the new bullet was slightly more stable than previous versions, but perhaps didn’t fly as far. This work could contribute to improving the design of future sports equipment.
Sports players know that millions of dollars in salary and potential endorsement deals can be at stake in every game. Footballers often complain about the aerodynamic properties of the ball because random flutter in flight can turn a harmless shot into a goal. Old school soccer balls have 32 panels, with a mix of hexagons and pentagons. More recently, top soccer leagues have experimented with 6-panel versions with stripes similar to a volleyball. For the new season, the English Premier League have introduced the Flight 2020 football from Nike, which is advertised as having molded grooves that provide consistent flight.
Now, researchers at the University of Tsukuba have tested those claims with wind tunnel experiments. They measured the drag coefficient of the bullet, along with two previous models, as a function of Reynolds number. The Reynolds number, an important parameter in fluid dynamics, controls the transition from smooth to turbulent flow. According to the author, Professor Takeshi Asai, “At low Reynolds numbers, smooth flow occurs, as viscosity can damp turbulence. At high Reynolds numbers, chaotic air swirls can lead to patterns unstable and unpredictable flights.”
The team found increased drag at high Reynolds numbers for the new bullet. This led to reduced flight range but may also have reduced lateral forces that can destabilize flight path. This was especially true in the “asymmetrical” orientation of the bullet, when one of the grooves was facing forward. “Flight 2020’s lower fluctuations in lateral and lift forces indicate that it is less likely to experience erratic changes in trajectory, which can lead to greater stability during flight,” says Professor Asai.
The team partially attributed this trade-off of stability at the expense of range to increased surface roughness. This discovery may be useful in designing other sports equipment to increase the importance of skill and reduce the impact of chance.
The work is published in Scientific Reports as “Newly Approved Football Aerodynamics for the 2020-21 English Premier League Season” (DOI: 10.1038/s41598-021-89162-y).