I'll only comment on a few points here. The main thing is, I agree with the
answers thus far with regards to VRS in an autorotation. It isn't going to
happen!

"The OTHER Kevin in San Diego" skiddz *AT* adelphia *DOT* net wrote in
message ...
On 20 Aug 2004 17:19:48 -0700, (Greg Johnson)
wrote:

3 things required for settling with power:

1) A high rate of descent. (appx 300 fpm in a "real" helo)

That is to say, a "full size" helo! The RC models "are" real helo's. They
have the same controls and are governed by the same aerodynamic rules as the
full size birds. Their biggest advantage, beyond not having to worry about
your arse if something goes wrong, is that the models generally have WAY
more power to weight than the big birds do and they are much stronger,
mechanically, and will take a lot more "relative" abuse than the full size
birds. SWP or VRS, been there, done that, with a RC model. Try smacking
the ground, level attitude, from a scale height of 20 feet in full VRS!
I've gotten away with this while learning to fly my model. Guarantee you
"won't" with the full size bird! ;-)

Only PART of the blade is generating significant lift, and it's only
enough to keep you from plummeting like a lawn dart.. The inner 25%
or so is stalled. Too much AOA to be of any use. The outer 30% or so
has too little AOA to be of much help. The middle 45% has an AOA
that's "just right" for providing significant lift.

Interesting!? The graphs I've seen that illustrate the lift patterns of the
rotor disk during autorotation show the inner 33% of the blade as a stalled
region. The middle 33% (roughly) is the "driving" region. That is, the
part of the blade that's providing the aerodynaminc thrust that maintains
the autorotative state and thus, the main rotor rpm. The outer 33% (again,
roughly) is the "driven" region. That is, the part of the rotor disk that's
providing the usable lift that slows the descent rate and allows attitude
control, thru pitch and roll cyclic, of the helicopter. As I recall, I got
this from an FAA helicopter manual for primary rotorcraft students. Has
that changed or are you working off a different text. It's been a "very"
long time and maybe this stuff's been updated. What text are you working
from, out of curiosity?

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.

Helicopter rotor blades create a wing tip vortex just like fixed wing
aircraft do. It trails off behind the aircraft just like the fixed wing
airplane. The heavier the helicopter, the more pronounced the vortex,
again, just like the fixed wing folks. It makes no difference if the
helicopter is in powered or autorotative flight. As long as the main rotor
blades are generating lift, the vortices will be there.

For the purposes of the subject line question, as others have stated, the
upward airflow thru the main rotor disk, as the helicopter descends in an
autorotation, keeps the VRS for establishing itself.

FWIW!
Fly Safe,
Steve R.