Plain English Meaning

A piece of yarn stuck to the outside of the windshield. The way it blows in the airflow tells the pilot whether the airplane is flying straight through the air or is angled slightly sideways.

Full Definition

A short length of yarn or string taped to the outside of the windshield or canopy that streams in the relative wind, providing a direct visual indication of whether the airplane is flying coordinated or sideslipping. When the string points straight back along the longitudinal axis, the airplane is in coordinated flight; when it points off to one side, the airplane is slipping or skidding in the opposite direction.

Context Anchor

Seen on some training airplanes, gliders, and as a simple for keeping the airplane aligned with the airflow, especially during .