The sport of rugby returns to the Olympics in Rio this year. Rugby’s ball is somewhat similar in size and shape to an American football, but it is a little wider and more rounded. Aerodynamically, this means that the rugby ball has more drag, but it is also more stable in flight, allowing players to pass and kick accurately, with or without a spiral.
As seen in the flow visualizations above, air travels up and around the ball before separating on the far side. The more the ball is tilted, the larger this separated region is and the greater the drag. At the same time, though, that tilt provides lift on the ball. The ideal orientation is the one with the largest ratio of lift force and drag force. For a rugby ball, this occurs at about 40 degrees.(Image credits: Planet Rugby; A. Vance et al.)
Previously: The aerodynamics of the American football