Downwash is defined as which of the following?

• A. air flowing upward into the wing from the front
• B. air flowing downward toward the leading edge
• C. air flowing down and away from the trailing edge of the wing as it leaves
• D. air flowing parallel to the wing surface

Answer: (C)

Downwash is the downward deflection of the airflow as it leaves the wing, creating a downward component in the wake behind the wing. This happens because lifting the wing pushes air downward, and the streamlines bend downward and then move away from the trailing edge. That is why the description of air flowing down and away from the trailing edge as it leaves best captures downwash. The other descriptions describe airflow directions that don’t reflect the downward deflection behind a lifting wing, such as flow upward toward the wing, downward toward the leading edge, or flow parallel to the wing surface. Downwash also relates to induced drag—the greater the lift, the greater the downward deflection in the wake.