Originally Posted by
B Fraser
Thanks for the correction, wrong terminology. I only did a few lessons in an R22 for fun. I thought that the downwash had to be balanced by an upwash somewhere else.
That is generally speaking correct. Vortex ring is a specific (and unhelpful) type of this equalising flow (which indeed always happens but ideally further outside the rotor disc). In Vortex Ring State it is if you like 'condensed' in a 'Donut' shape around the tip plane of the rotor. So instead of the thrust going straight down it quickly dissipates to the outside and back to the top of the rotor disc, thereby significantly reducing effective vertical mass flow and thus thrust of the rotor disc.