 For systems that are hinged at some distance from the axis of rotation (such as a fully articulated rotor head) the phase lag is less than 90 degrees.In forward flight the pilot will experience either a right or left roll (see flight dynamics), depending upon whether the rotor of the helicopter rotates counter-clockwise or clockwise.Which way the helicopter rotor disk moves against the direction of the relative wind will determine which part of the disk has higher lift.