Which of the following statements best describes the role of downwash in lift generation and drag?

• A. Downwash is a consequence of wing circulation that reduces effective angle of attack and contributes to induced drag.
• B. Downwash increases lift without drag.
• C. Downwash has no impact on lift or drag.
• D. Downwash only occurs at supersonic speeds.

Answer: (C)

Downwash is the downward deflection of the airflow downstream of a lifting wing, produced by the wing’s circulation. This downward flow means the air that passes over the wing effectively bends downward, so the wing experiences a smaller angle between its chord line and the actual flow than the free-stream direction. Lift arises from that circulation, and as lift increases, the downwash strengthens. The stronger downwash, in turn, imparts downward momentum to the air and creates a drag component known as induced drag. In short, downwash is a direct result of the wing’s circulation, it reduces the effective angle of attack the wing feels, and it contributes to induced drag. This phenomenon occurs at subsonic speeds as well, not just at supersonic speeds.