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.
Plain English
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.
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.