Simply said, Vortex Ring State is the condition that occurs when the rotor is descending into its own down wash. In autorotation, the rotor is descending far faster than that, so that there is no downwash at all, there is up wash as the rotor is spun by the column of rising air around it.
In other words, VRS cannot possibly occur in an autorotation.
Also, VRS can only occur when the rotor is descending at 70% of the downwash speed, which is over 700 fpm for a robbie and 3000 fpm for a Black Hawk, and somehwere in between for most helicopters.
What people generally call VRS is usually where they are at near hover and unable to sustain a hover, so they fall through and descend.
Last edited by NickLappos; 20th Mar 2017 at 01:47.