Definition
The intensity of the rotating air masses (wingtip vortices) trailing behind an aircraft in flight, determined primarily by the generating aircraft's weight, speed, and wing shape. Vortex strength increases as weight increases, as speed decreases, and when the wing is in a clean configuration (flaps and gear retracted). The heaviest, slowest, cleanest aircraft produces the strongest vortices.
Plain English
How powerful the spinning air left behind an aircraft is. A heavy airliner flying slowly with its flaps up leaves behind very strong spinning air; a small, fast aircraft with flaps down leaves much weaker spinning air.
Context Anchor
Seen in wake turbulence discussions, especially when taking off, landing, or following another aircraft near a runway.
Derivation
Vortex comes from the Latin vortex/vertex, meaning a whirling mass or whirlpool. The word captures the spinning, funnel-like motion of the air shed from the wingtips.
Why Pilots Care
Stronger vortices create more hazardous wake turbulence that can roll or pitch a following aircraft.
Analogy
Similar to the powerful swirling wake a large ship leaves behind it in the water.
Grounding Statement
Picture a large jet lifting off ahead of you: the stronger its vortices are, the more powerful the invisible rolling air left behind it can be.
Intuition Check
Do not read strength as engine power or how strong the airplane is. Here, strength means how intense the spinning wake air is.
Example Sentence 1
The controller spaced us well behind the heavy jet on final because its vortex strength would be greatest in the landing configuration at low speed.
Example Sentence 2
Vortex strength increases at slower approach speeds because the wing must work harder to produce lift.