Also known as blade pitch angle, the ______ is the angle between the chord line of a blade and the rotor hub.

• A. Angle of incidence
• B. Resultant relative wind
• C. Angle of attack
• D. Total aerodynamic force

Answer: (A)

The concept being tested is how the blade is pitched relative to the rotor hub. The blade pitch angle, which is also called the incidence, is the angle between the blade’s chord line and the rotor hub. It’s a geometric measure of how the blade is mounted and pitched, independent of the wind hitting the blade.

The angle of attack, by contrast, is the angle between the blade’s chord line and the actual airflow (the relative wind). That angle depends on airspeed, rotor inflow, and flight condition, and it governs the lift produced by the airfoil section at that moment.

The other terms described aren’t angles: resultant relative wind describes the airflow direction, and total aerodynamic force is a force vector acting on the blade.