The brothers decided to find out if Lilienthal's data for lift coefficients were correct. They devised an experimental apparatus which consisted of a freely rotating bicycle wheel mounted horizontally in front of the handlebars of a bicycle. The brothers took turns pedaling the bicycle vigorously, creating air flow over the horizontal wheel. Attached vertically to the wheel were an airfoil and a flat plate mounted 90° away. As air passed by the airfoil, the lift it generated, if unopposed, would cause the wheel to rotate. The flat plate was oriented so its drag would push the wheel in the opposite direction of the airfoil. The airfoil and flat plate were made in specific sizes such that, according to Lilienthal's measurements, the lift generated by the airfoil would exactly counterbalance the drag generated by the flat plate and the wheel would not turn. However, when the brothers tested the device, the wheel did turn. The experiment confirmed their suspicion that either the standard Smeaton coefficient or Lilienthal's coefficients of lift and drag—or all of them—were in error.