It it possible to get into vortex ring state (or settling with power)
during an autorotation?

A friend at my radio control helicopter field claimed that you shouldn't
do a vertical autorotation, because you might enter vortex ring state
if you do.

This doesn't seem right to me based on my limited knowledge of the
aerodynamics of helicopters.

Clearly, during an autorotation the main blades are developing lift, just
like a glider's wings are generating lift when it descends at a constant
velocity.

And so, presumably there is a vortex at the tips of the blades. But in an
auto, it seems like you would be descending out of this rotor tip vortex;
the wind is driving the blades, rather than the blades driving the wind.

Furthermore, the inner counter-rotating vortex that develops during
vortex ring state would seem not to be possible during an auto, because
there is no down-wash over the intermediate part of the blades. The air
is going up through the rotor disk the whole way out from blade roots
to tips.

(This is all just seat-of-pants intuition; I hope someone with aerodynamic
knowledge can say if my intuition is right, and what the aerodynamics
of an auto are, and why in that regime settling with power can't happen.)

The one place I can (just barely) imagine it might be possible is during
the brief moment at the bottom of an auto when you crank up the collective
to exchange rotational inertia for lift to cushion your landing. At that
point it seems like you are adding energy to the rotor head other than
that which is coming from the descent through the air. My supposition
is that you can turn the blades using the engine, or you can turn
the blades using the stored rotational inertia in the blades, and in
either case you might be able to induce vortex ring state. Is this true?

Thanks a million for any thoughts or comments,

Greg