Definition
The way air is deflected downward as it leaves the trailing edge of a wing or flap. The angle, strength, and pattern of this downward-flowing air change with airspeed, angle of attack, and flap setting, and these changes affect lift production, drag, and the airflow reaching the tail surfaces.
Plain English
How the air gets pushed downward behind the wing, and how that downward push changes depending on what the wing and flaps are doing.
Context Anchor
Seen when learning how flap extension affects lift, drag, and pitch during takeoff, approach, and landing.
Derivation
Down + wash. 'Wash' here comes from the older sense of moving fluid or air sweeping past something — the same idea as the 'wash' behind a boat. So 'downwash' is simply the air being washed downward off the wing.
Why Pilots Care
Changes in downwash behavior directly influence pitch attitude, control feel, and stall speed when flaps are extended.
Grounding Statement
A wing makes lift by pushing air downward; downwash behavior is simply how that downward push is shaped and where it goes.
Intuition Check
Do not read “behavior” as a human-style action or habit. Here it means the way the downward airflow changes and affects the airplane.
Example Sentence 1
When the flaps were lowered for landing, the change in downwash behavior caused the nose to pitch slightly, requiring a small trim adjustment.
Example Sentence 2
Understanding downwash behavior helps explain why the airplane pitches nose-up when flaps are extended at constant airspeed.