Autorotation ? R22 for the Experts

Here is a good question for the more experienced helicopter pilot or
mechanic. A friend of mine that flies a late model Robison R22 Beta
II asked this question of a number of individuals and no one seem to
have an explanation. This included people at the manufacturer. I
believe I know the answer, however, I would like to put the question
out and see what others think before tainting their thoughts with my
ideas.

So here is the question: With one person flying the R22 (170lb),
simulating an autorotation by rolling off throttle, the collective
goes full down and pretty-much stays there to maintain proper rotor
rpm. With two people, same maneuver, some collective has to be pulled
to keep the main rotor from over-speeding. The amount of collective
will obviously vary dependent on a number of factors, but for this
example let's say about 1 inch off the stop. One more time with the
same maneuver, with two on board, except let the governor control
engine speed, and not rolling off throttle. In order to maintain
rotor speed the collective has to be on the stop. The question is
why? Please post your thoughts.

Thanks,

Eric D

In the first instance, you are not "simulating" an autorotation; with no
engine OR no engine power applied to the rotor (throttle rolled off) you are
"performing" an autorotation. With the engine throttle left in a flight
position, the governor is GOVERNING rotor R.P.M. due to it's linkage to the
collective and the engine which is what under any circumstances what it
ACTUALLY GOVERNS, and ONLY THEREFORE can govern your rotor R.P.M.
SO...collective bottomed...engine "running", governor GOVERNS rotor R.P.M.
NO engine running (or no throttle applied) YOU govern rotor R.P.M. The
other variables you alluded to will include gross weight per fuel on board,
etc.
Bob

"Bob" wrote in message ...
In the first instance, you are not "simulating" an autorotation; with no
engine OR no engine power applied to the rotor (throttle rolled off) you are
"performing" an autorotation. With the engine throttle left in a flight
position, the governor is GOVERNING rotor R.P.M. due to it's linkage to the
collective and the engine which is what under any circumstances what it
ACTUALLY GOVERNS, and ONLY THEREFORE can govern your rotor R.P.M.
SO...collective bottomed...engine "running", governor GOVERNS rotor R.P.M.
NO engine running (or no throttle applied) YOU govern rotor R.P.M. The
other variables you alluded to will include gross weight per fuel on board,
etc.
Bob

One pob = collective fully down to maintain rotor speed.
Two pob = collective not fully down to prevent overspeed.

If helicopter is heavier will not the coning angle be greater and
therefore the rotor speed higher because of less effective rotor
diameter. Hence the need to pull some collective at heavier weight to
slow blades and increase rotor disk diameter?

Or maybe I'm talking b****x! It has been known!!
Herbie

Herbie...
YES. BUT...that wasn't the question. The question was given
weight-throttle on vs. given weight-throttle off.

Bob

"Bob" wrote in message
news
Herbie...
YES. BUT...that wasn't the question. The question was given
weight-throttle on vs. given weight-throttle off.

Bob



I'm not sure I'm getting this either. The original poster was confused
because, engine out of the equation, they had to "raise" the collective to
prevent an overspeed. With the engine / governor still in the equation,
they "didn't" have to raise the collective to prevent an overspeed.

Now, if the collective is bottomed out and the MR blades are at an
autorotative angle, wouldn't the rotor system try to outrun the engine /
drive system? Or, is the engine acting as a brake in the situation, kind of
like a car coasting downhill, using engine compressionas a brake?

Just wondering?
Fly Safe,
Steve R.

And come to think of it...actually NO. Collective down, there's no cone to
speak of or your rotor speed would be drooping.

"Bob" wrote in message
...
And come to think of it...actually NO. Collective down, there's no cone
to
speak of or your rotor speed would be drooping.



No cone? I'm not sure I agree with that. Even with the collective all the
way down, there's still positive lift being generated by the rotor system.
Maybe the coneing angle isn't what it would be in steady state, powered
flight but I'm not sure it's accurate to say that there's "no" coning with
the collective full down.

Fly Safe,
Steve R.

Steve...
Kindly read my post carefully. I said NO CONE TO SPEAK OF. As in...it
would not to compare to the cone present when trying to yank the helicopter
off the ground at Max Gross Weight. The lift generated with the collective
down is what keeps your rate of decent an "autorotative" rate, rather at
terminal velocity

As to your other post...when the collective is down with no engine power (on
a real helicopter) the pitch links are adjusted to keep the auto-R.P.M.
within an acceptable RANGE. That is a standard maintenance function, but it
dosn't mean the pilot can go to sleep during an auto. Collective down, if
rpm is too high- it's not adjusted properly, but the pilot can jockey the
collective. If its too low it's DEFINATELY not adjusted properly and rots
o' ruck.

In my first post in this string ALL I was trying (apparently not too
clearly) to explain is that if the engine is running (at all) the governor
knows it. I am a heavy helicopter maintenance type and can't even spell
Robinson, BUT even the most "rudimentary" if you will, helicopters have to
operate with some derivation of dynamic principles and proven hardware
concept application. The bottom line is in an auto, to keep the rotor in
the green right off. Too High is always better than Too Low because the
pilot can fix that.

Good luck,
Bob

First off, thanks to everyone that has responded to my original
posting.

Bob, Your response was super, and I understood what you wrote. I
believe what you described is right on the money for larger aircraft
that you mentioned you worked on.

The governor on the Robison R22 Beta II does not have linkage to the
collective. The scenario I described in my original post is due to
the sprag clutch. During low overrun speeds there is some drag
through the sprag. As the overrun speed increase this drag decreases.
To clarify, when speaking of overrun speed, it is the velocity across
the sprag clutch, not rotor speed.

I have limited helicopter maintenance experience on anything larger
then a Robinson R44. I received my A&P in the early seventies and
also have IA. I have worked on many types of aircraft over the years.
My passion for Robinsons came about four years ago, so I'm still
learning. I also have a fixed wing pilot's license and I have started
working on learning how to fly an R22. I'm finding it a blast and I
am really enjoying it.

Thanks again for the great responses,

Eric D

And THANK YOU ERIC. Thought the dog ate ya, and I've been up to my ears
since I replied to your first question. Out of courtesy to the group, I'll
still consider whatever aircraft you were addressing a, uhhhhhh, helicopter
and leave the rest of this mess in your hands. If there was any help on my
part, you're most welcome.

Happy flying or whatever that contraption does