Nick,
I didn't mean to imply VRS in an autorotation. The idea here is to transition from autorotation to a powered hover (using engine power, obviously). Once the engine is providing power, the ROD will still be near to what the ROD during autorotation was, hence my reference to the autorotation ROD.
As far as what Thomas Coupling meant, he's the best judge, but he did say, "An engine running auto to a full stop in the hover...[VRS] wouldnt have time to precipitate." Doesn't sound like an auto to touchdown to me.
Mr Selfish,
You\'re right that its a compromise between minimizing ROD and maintaining Nr. If you\'re authorized to do zero speed autos you can determine what ROD and Nr will stabilize and how quickly it will happen. However, the Nr will decay quite quickly if you\'re hovering OGE and to reach a stabilized condition you first need an even lower collective to recover Nr, then increase to maintain.
I did these in a 206 starting at 10 feet - not difficult, increasing to 30 feet - things happening quickly, but minimal loss of Nr...more difficult, then to 50 feet - again things happening quickly, more loss of Nr...most difficult (of what I tried), and finally from about 75 feet...entry the same, time to stabilize, time to peek inside and see what\'s happening...less difficult than 50 and maybe 30 feet. Any higher and I\'d extrapolate that the stabilized condition just lasts longer or you\'d opt to achieve forward flight.
In a Gazelle, I did these from 2 feet up to almost 10 feet. It was not comfortable above 5 feet. Rotor decay didn\'t seem to end and the reduction in collective effectiveness was dramatic.
Technique then is to learn from type experts about what works for what you\'re flying. In general, you\'d have to recover Nr with the lowest collective comfortable, then raise to stabilize, and check at the \"right\" height. Very much a learned technique not a written one.