What is "vortex ring state" (also called "settling with power") and under what conditions is a multirotor most vulnerable to it?
Why →
Vortex ring state (VRS) occurs when the rotor system descends into its own downwash vortices. The rotor is producing thrust but the downwash is circulating back into the rotor disk, severely reducing efficiency. Conditions: slow vertical descent rate (300–500 fpm), low forward airspeed, power applied. Recovery requires forward airspeed to fly out of the recirculating vortex. For multirotors, VRS can cause rapid, unexpected altitude loss that the flight controller struggles to compensate.The trap →
Ground effect (Choice A) is the opposite scenario. Hovering near the surface in undisturbed air. VRS is an airborne, power-on vertical descent condition, not a landing phenomenon. High-speed forward flight is protective against VRS since forward speed moves the rotor out of its own downwash.SOURCE → FAA Helicopter Flying Handbook, Aerodynamics conceptsCHECKED APR 21ACS IV.A.K1MED