the pitch angle of the blade is the difference in angle between the chord line and the reference datum. the reference datum is an imaginary line perpendicular to the rotor mast. angle of attack is the difference in angle between the chord lie and the relative wind
relative wind is the combination of all airflow over an airfoil. in the case of a helicopter reletive wind comes from the rotation of the rotor head, movement of the helicopter in any direction, atmospheric wind, induced flow from the creation of lift and from flapping or leading and lagging
