Which term describes the flow direction and speed of air approaching the airfoil?

• A. Airflow
• B. Wind Speed
• C. Relative Wind
• D. Air Mass

Answer: (C)

Relative wind is the flow of air as it approaches the airfoil, taking into account both the direction from which the air is coming and how fast it is moving relative to the aircraft. This is the air the wing actually “feels,” and it determines how lift and drag develop because the wing’s angle of attack interacts with that incoming air. The speed of the relative wind equals the aircraft’s airspeed, and its direction is opposite to the aircraft’s velocity through the air, adjusted for any wind.

Airflow is a general term for moving air and doesn’t specify relative to the aircraft. Wind speed refers to air movement relative to the ground, not the aircraft, so it doesn’t capture the airplane’s frame of reference. An air mass is a large body of air with uniform properties, not the flow character at the wing.