Definition
The downward deflection of airflow behind a wing as it produces lift. As the wing pushes air down, that mass of air leaves the trailing edge angled downward relative to the free airstream, and this downward-angled flow is called downwash.
Plain English
When a wing makes lift, it pushes air downward. The air leaving the back of the wing is now moving slightly downward instead of straight back. That downward-moving air behind the wing is the downwash.
Context Anchor
Seen in discussions of flaps, lift, pitch changes, and how airflow from the wing affects the tail of the airplane.
Derivation
‘Downwash’ is a plain compound: ‘down’ plus ‘wash,’ where ‘wash’ here means a stream or current of moving air or water (as in ‘the wash from a boat’). So it literally means the downward stream of air left behind by the wing.
Why Pilots Care
Increased downwash from flap use changes the airflow over the tail, often requiring nose-down trim and altering pitch stability during approach and landing.
Grounding Statement
Picture the wing leaving a slanted stream of air behind it, with that stream angled downward instead of straight back.
Intuition Check
Wing downwash is not propeller blast and not air simply falling off the wing. It is airflow turned downward because the wing is producing lift.
Example Sentence 1
Lowering the flaps increased the wing downwash, which struck the tail at a different angle and caused a slight pitch change.
Example Sentence 2
The pilot compensates for stronger wing downwash on final approach by applying nose-down trim to maintain the desired pitch attitude.