Definition
The natural tendency of an aircraft on the ground, or in flight under certain conditions, to align its longitudinal axis (nose) into the relative wind, pivoting about its vertical axis like a wind vane on a rooftop. On the ground, this is most noticeable during taxi, takeoff, or landing in a crosswind, when the larger side area behind the pivot point (main wheels) causes the tail to swing downwind and the nose to swing into the wind.
Plain English
When wind hits the side of an aircraft, the aircraft tries to turn its nose into the wind, the same way a rooftop wind vane points into the breeze.
Context Anchor
Seen in discussions of directional stability, yawing, and how the vertical tail helps keep an airplane aligned with the airflow.
Derivation
From the old rooftop 'weather vane' — a free-pivoting arrow that turns to point into the wind. The aircraft behaves the same way: more surface area behind the pivot than in front, so the wind pushes the tail downwind and the nose lines up with the wind.
Why Pilots Care
It supplies inherent directional stability that helps the aircraft hold a straight path with less pilot input.
Grounding Statement
Picture a side gust pushing the tail; the tail’s side area helps swing the nose back toward the airflow, much like a weather vane turning into the wind.
Intuition Check
Do not read weather vane here as a weather instrument for forecasting. In this context, it means something that turns to line up with the wind or airflow.
Example Sentence 1
On the takeoff roll in a strong left crosswind, the aircraft tried to weather vane into the wind, so the pilot held right rudder to stay aligned with the centerline.
Example Sentence 2
Directional stability from the weather vane effect kept the nose aligned after a brief yaw disturbance.