A crop header has generally horizontal flail disks mounted for driven rotation about generally upright axes of a cutter bar. A tilting system is provided for tilting the cutter bar about an axis transverse to the machine so as to tilt the cutting plane from a generally horizontal position forwardly and rearwardly. A sensor is provided which is responsive to upward and downward floating movement of the cutter bar relative to the support frame and is arranged to analyze changes in the signal to determine times when the cutter bar is moving upwardly when the cutter bar is tilted rearwardly, times when the cutter bar is moving downwardly when the cutter bar is tilted forwardly and times when the cutter bar is remaining at a constant height.
