Refer to figures.

1. Blade Angle of Attack
   The path of the propeller through the air determines the direction of the relative airflow. The angle between the blade chord and the relative airflow is the angle of attack. The angle of attack varies as a function of propeller rotational velocity (RPM) and aircraft forward velocity (TAS).
2. The Blade Angle
   Sometimes called the pitch angle or blade pitch, is the angle between the plane of rotation and the chord line of the propeller blade, which may be fixed or variable. Blade angle = helix angle + blade angle of attack.
3. The Helix Angle
   The angle that the actual path of the propeller makes relative to the plane of rotation. Helix angle = Blade angle - blade angle of attack