Hi there,
Vortex ring is a state of power on flight if you like when you injest your own downwash,an amusing feeling I used to get when flaring downwind in an old Bell 47j Ranger many moons ago.Fortunatly,helicopters like the R22 are hard to vortex ring but that never stops me showing my students as if you try hard enough,you will find that they all will vortex ring given right conditions!!Bye the way,its hard to recover your rrpm from low altitude in big bladed machines when vortex ring occurs,this is because most of us mortals try and arrest the ROD with collective which only makes the situation worse!Hope this is of help.