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An angular oscillation of a rotor blade in the plane of rotation about a substantially vertical axis. The fore-and-aft movement of the tip of a helicopter rotor blade in its plane of rotation. Lead-lag motion is the freedom given to each blade of a rotor to allow it to move in the plane of rotation independently of other blades. This is to avoid bending stress at the root. The blade is allowed to lead or lag about a dragging hinge, but movement of the hinge is restricted by some form of drag damper to avoid undesirable oscillations. Also known as dragging or drag. See drag (ii).