Private Pilot License (PPL) Aerodynamics Practice Exam

How is the angle of attack for a propeller defined?

1. The angle between the propeller and the ground

2. The angle between the propeller chord line and the relative wind

3. The angle formed by the pitch of the propeller blades

4. The angle between the propeller and the airplane's fuselage

The correct answer is: The angle between the propeller chord line and the relative wind

The angle of attack for a propeller is defined as the angle between the propeller chord line and the relative wind. This concept is similar to the angle of attack in aerodynamics concerning an aircraft wing. It is a critical parameter because it determines the amount of lift generated by the propeller blades as they cut through the air. When the angle of attack is increased, the blades can generate more lift up to a certain point, beyond which the propeller may stall, similar to a wing stalling. The relative wind is the airflow that the propeller encounters as the aircraft moves through the air, which is essential for understanding how effectively the propeller will convert engine power into thrust. This definition highlights the importance of the relationship between the propeller blades and the airflow, as it governs the efficiency and performance of the propeller in generating thrust for the aircraft. Thus, recognizing the correct geometric relationship is crucial for pilots to optimize thrust and performance during flight operations.