Plain English Meaning
The wing is intentionally twisted so the outer end meets the air at a slightly steeper angle than the inner end, making the tip lift harder than the root.
Full Definition
A built-in twist along the span of a wing that increases the angle of incidence toward the wingtip, causing the tip to produce more lift than the root for a given airflow.
Context Anchor
Seen in aircraft rigging, maintenance checks, and discussions of wing handling or stall behavior.
Derivation
From the rigging term 'wash,' meaning a built-in twist or set in a wing or blade. 'Wash-in' indicates the twist increases the angle toward the tip, the opposite of 'wash-out,' where the tip is twisted to a lower angle.
Why Pilots Care
Changes stall progression and roll behavior; improper wash-in can create unwanted handling quirks or reduce aileron effectiveness near the stall.
Intuition Check
Wash-in does not mean cleaning the wing. It means the wing is twisted so the tip sits at a higher angle than the inner wing.
Example Sentence 1
A small amount of wash-in on the left wing helps offset the rolling tendency caused by engine torque at cruise power.
Example Sentence 2
With wash-in applied, the wing root stalls before the tip, preserving aileron control deeper into the stall regime.