What is the direction of movement of the atmosphere relative to an airfoil?

• A. Upwash
• B. Relative wind
• C. Downwash
• D. Angle of attack

Answer: (B)

The atmosphere moves relative to the airfoil as the relative wind. When the airplane flies forward, the air appears to flow toward the aircraft from in front and past the wing toward the tail. This incoming flow is what the wing “sees,” and it defines the wing’s angle of attack—the angle between this relative wind and the wing’s chord. Upwash and downwash describe how the airflow is deflected by the wing around the leading and trailing edges, not the overall direction of the air moving past the wing. So the correct concept is the relative wind.