Editing Vortex ring (section)

===Vortex ring state in helicopters===
{{main|Vortex ring state}}
[[File:Vortex ring helicopter.jpg|thumb|The curved arrows indicate airflow circulation about the rotor disc.  The helicopter shown is the [[RAH-66 Comanche]].]]
Air vortices can form around the [[helicopter rotor|main rotor]] of a [[helicopter]], causing a dangerous condition known as [[vortex ring state]] (VRS) or "settling with power".  In this condition, air that moves down through the rotor turns outward, then up, inward, and then down through the rotor again. This re-circulation of flow can negate much of the lifting force and cause a catastrophic loss of altitude.  Applying more power (increasing collective pitch) serves to further accelerate the downwash through which the main-rotor is descending, exacerbating the condition.