Definition
The tendency of a moving fluid, such as air, to follow the contour of a nearby curved surface rather than continuing in a straight line. As the fluid bends around the surface, its velocity increases and its pressure decreases, which can produce lift or alter airflow direction.
Plain English
Air that flows past a curved surface tends to stick to that surface and follow its shape instead of going straight. This bending of the airflow can create useful aerodynamic forces.
Context Anchor
Seen in aerodynamics discussions, especially when learning how air moves over wings, flaps, and other curved aircraft surfaces.
Derivation
Named after Romanian aerodynamicist Henri Coandă, who observed and described the phenomenon in the early 1900s while experimenting with early jet aircraft. Knowing the name comes from a person, not a Latin or Greek root, helps avoid trying to decode it linguistically.
Why Pilots Care
It explains how airflow can stay attached over the curved upper surface of a wing, contributing to lift and helping delay stall.
Analogy
Hold the back of a spoon under a thin stream of water from the tap. Instead of deflecting away, the water curves and clings to the spoon. That clinging is the Coanda Effect.
Grounding Statement
Picture air flowing over the curved top of a wing and staying close to the surface for a while instead of flying off in a straight line.
Intuition Check
Do not think of the Coanda Effect as air being glued to the aircraft. It means moving air tends to follow a curved surface under the right conditions, but it can still break away if the curve is too sharp or the airflow is disturbed.
Example Sentence 1
The designers used the Coanda Effect to keep airflow attached over the flap, increasing lift at low speeds.
Example Sentence 2
Some high-lift devices use the Coanda Effect to direct air over flaps and keep the boundary layer attached.