Definition
The downward deflection of airflow behind a wing that is producing lift. As the wing generates lift, higher-pressure air beneath it spills around the wingtips into the lower-pressure area above, and the bulk airflow leaving the trailing edge is angled downward. This downward-deflected airflow is called induced downwash, and it is the direct by-product of producing lift.
Plain English
When a wing makes lift, it pushes air downward as it passes by. That downward-flowing air behind the wing is called induced downwash. It only exists because the wing is producing lift.
Context Anchor
Seen in discussions of wingtip vortices, induced drag, slow flight, and high angle-of-attack flight.
Derivation
Induced means 'brought about by' — the downwash is brought about by the wing producing lift. Downwash simply describes air being washed downward. Together: the downward airflow caused by lift production.
Why Pilots Care
It increases induced drag and requires pilots to anticipate its effects on following aircraft and on their own airplane's efficiency at low speeds.
Grounding Statement
Picture the wing lifting the airplane by pushing air downward; the downward flow left behind is induced downwash.
Intuition Check
Induced downwash is not just any air moving downward. It is the downward airflow caused by the wing producing lift.
Example Sentence 1
At high angles of attack, induced downwash increases, which is one reason induced drag rises sharply during slow flight.
Example Sentence 2
A pilot flying behind a large aircraft must allow extra spacing to avoid the effects of its induced downwash.