"The OTHER Kevin in San Diego" skiddz "AT" adelphia "DOT" net wrote in
message ...
On Thu, 18 May 2006 01:18:37 GMT, boB
wrote:


Of course you can apply collective and slow the decent rate if you have
enough power. The rotor wash does not increase equal to the amount of
power applied. You don't "increases the sink rate" unless there is no
power left.

Every text I've read and every high time (10,000+ hour) heli pilot
I've spoken to disagrees with that statement

My experience on the stick (limited as it is) clearly shows the sink
rate increases as you pull pitch when you're in the downwash.


I agree! I know some full size pilots around here won't take this seriously
because it didn't happen with a 100% scale machine but, I've had this happen
with an RC model. We had mounted a camera system to an RC model (a Bergen
Observer, www.bergenrc.com if you're curious) and was using it to do aerial
inspections. We had a video downlink on the machine so the camera operator
(there were two RC control systems, one to fly the helicopter and one to
operate the camera pan, tilt, zoom, and shutter functions) could see what he
was taking pictures of.

The machine flew Ok but it was carrying about as much weight as could be
expected. It was mid summer so temps and humidity were in the upper 90's
(can we say, "high" density altitudes!) and it was a "dead calm" day.
Absolutely no wind to speak of so no help from ETL in an OGE hover. At one
point, the camera operator needed me to do a vertical descent. I lowered
the collective and it started down. For the record, I was trying to be
gentle with this. When he said, that's good, I raised the collective back
up to stop the descent. Needless to say, it didn't work. Next thing I
know, the model was dropping "very" fast. I understood what was happening.
The rotor blades, which are normally relatively quiet, were really mixing it
up. I finally applied full cyclic to move off the column of air I was
descending in and found, to my total horror, that it didn't seem to be
working. At full control input, that model should have come close to doing
a flip, right there. It seems that when the rotor is in full on vortex ring
state, cyclic authority goes way down too. It did eventually react and fell
off to one side. When the rotor blades finally caught clean air, there was a
loud aerodynamic pop and the model shot off in that direction. It was very
close. The model started at about 300 ft and recovered around 75 ft. The
rate of descent was truly amazing and the entire ordeal couldn't have lasted
more than a couple of seconds. We were "very" lucky!

The advantage you full size pilots have is that you're "in" the machine.
I'd imagine that you can feel this coming on, or have other clues to warn
you about it's inception. Flying a model helicopter is a totally visual
exercise. I had no warning that this was going to happen until after it
started and then it took a split second to recognize what was going on. If
it hadn't been for all the reading I'd done on helicopter aerodynamics back
when I was learning to fly the models, I wouldn't have had a clue as to what
was happening and what to do about it. I would have buried the model and
about $10k worth of electronics right along with it.

I know this much. I never want to repeat that experience and I "certainly"
NEVER want to experience it in a full size machine with "my" butt on the
line!

FWIW,
Fly Safe,
Steve R.