Definition
Small swirling, circular movements of air that form when smooth airflow is disrupted, typically where two airflows meet at different speeds or directions, such as at the junction of the wing and fuselage. These swirls disturb the surrounding airflow and contribute to interference drag.
Plain English
Tiny whirlpools of air that form when smooth-flowing air gets stirred up, usually where one part of the aircraft meets another. These little swirls add resistance to the airplane's motion through the air.
Context Anchor
Seen in discussions of drag, especially interference drag around places where parts of the airplane join, such as the wing and fuselage.
Derivation
From Old English 'ed-' meaning 'back' or 'again' — the same root as in 'edit' (to bring back). An eddy is air or water that turns back on itself instead of flowing straight, which is exactly what these little swirls do.
Why Pilots Care
Eddy currents increase total drag, reducing the airplane's efficiency and requiring more power to maintain altitude and speed.
Analogy
Think of a stream flowing past a rock — small whirlpools form just behind the rock where the smooth flow is disturbed. The same thing happens in air around aircraft junctions.
Intuition Check
Do not think of eddy currents as electrical current here. In this context, they are swirling currents of air caused by disturbed airflow.
Example Sentence 1
Wing-root fairings are installed to reduce the eddy currents that form where the wing meets the fuselage.
Example Sentence 2
Streamlined fairings at component junctions help prevent eddy currents from forming.