Thanks Nick, I’ve been hounding this “urban legend” for years. Let me take a stab.
Vortex Ring State (VRS) is a condition where the rotor ingests it's own vortices. This of course, is an over simplification. But what makes matters worse, VRS is a relatively unstudied phenomenon--just ask anyone in the V-22 program office.
During powered flight the airflow moves through the rotor system from above to below. When airflow is moving from below to above the rotor, we call this condition autorotation. VRS is entered when the flow is roughly between these two situations.
So it follows, to enter VRS, the airflow through the rotor needs to approach that of the rotor downwash. The rate of downwash is related to disc loading—but how fast are you entering this quick stop? More importantly, the movement of air needs to be nearly vertical through the rotor system. How far up is your nose during the quick stop? 85 degrees? Because 45 probably doesn’t cut it.
Now, it is typically understood that a helicopter is vulnerable to "Settling with Power" (I like the "over-pitching" term too) when the following 3 conditions are present:
(1) 20 to 100% power applied.
(2) Zero, or near zero airspeed (not ground speed).
(3) Rates of decent of 300 fpm or greater.
Isn’t this what you’re talking about (especially if your rotorcraft is underpowered and/or heavily loaded)?
VRS and Settling With Power are NOT the same thing, but are typically confused with each other because most pilots learn of them coincidentally. Doubt this? Think of it this way; if you agree about the 3 conditions for SWP above, then relate them to the conditions during a normal approach. Is a normal approach SWP? Is a normal approach VRS?