vortex ring state at any point during an auto??

It it possible to get into vortex ring state (or settling with power)
during an autorotation?

A friend at my radio control helicopter field claimed that you shouldn't
do a vertical autorotation, because you might enter vortex ring state
if you do.

This doesn't seem right to me based on my limited knowledge of the
aerodynamics of helicopters.

Clearly, during an autorotation the main blades are developing lift, just
like a glider's wings are generating lift when it descends at a constant
velocity.

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.

Furthermore, the inner counter-rotating vortex that develops during
vortex ring state would seem not to be possible during an auto, because
there is no down-wash over the intermediate part of the blades. The air
is going up through the rotor disk the whole way out from blade roots
to tips.

(This is all just seat-of-pants intuition; I hope someone with aerodynamic
knowledge can say if my intuition is right, and what the aerodynamics
of an auto are, and why in that regime settling with power can't happen.)

The one place I can (just barely) imagine it might be possible is during
the brief moment at the bottom of an auto when you crank up the collective
to exchange rotational inertia for lift to cushion your landing. At that
point it seems like you are adding energy to the rotor head other than
that which is coming from the descent through the air. My supposition
is that you can turn the blades using the engine, or you can turn
the blades using the stored rotational inertia in the blades, and in
either case you might be able to induce vortex ring state. Is this true?

Thanks a million for any thoughts or comments,

Greg

"Greg Johnson" wrote in message
m...
It it possible to get into vortex ring state (or settling with power)
during an autorotation?

No.

A friend at my radio control helicopter field claimed that you shouldn't
do a vertical autorotation, because you might enter vortex ring state
if you do.

He's talking ********. To reach "that" stage, the air must be travelling
DOWNWARDS through the rotors. In autorotaion, the air is travelling UPWARDS
and turning the blade. (Well the AIRFLOW is upwards due to the downwards
trajectory of the heli)

This doesn't seem right to me based on my limited knowledge of the
aerodynamics of helicopters.

You're right, its not right.

Clearly, during an autorotation the main blades are developing lift, just
like a glider's wings are generating lift when it descends at a constant
velocity.

Exactamundo (almost:-)

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.

Correct.

Furthermore, the inner counter-rotating vortex that develops during
vortex ring state would seem not to be possible during an auto, because
there is no down-wash over the intermediate part of the blades.


Or over any part of the whole machine.

The air
is going up through the rotor disk the whole way out from blade roots
to tips.

Indeed it is, and one day I'll read the whole bleeding post before I start
typing :-))) save myself a lot of work if I did:-)


(This is all just seat-of-pants intuition; I hope someone with aerodynamic
knowledge can say if my intuition is right, and what the aerodynamics
of an auto are, and why in that regime settling with power can't happen.)

The seat of your pants is working well from where it's sitting:-)

The one place I can (just barely) imagine it might be possible is during
the brief moment at the bottom of an auto when you crank up the collective
to exchange rotational inertia for lift to cushion your landing.

Not going to happen there either. You need to have POWER into the blades
(and lot of it) plus a descent rate exceeding 300fpm.

At that
point it seems like you are adding energy to the rotor head other than
that which is coming from the descent through the air.

Actually, you're USING the energy already stored, so you're losing energy
not adding to it.

My supposition
is that you can turn the blades using the engine, or you can turn
the blades using the stored rotational inertia in the blades, and in
either case you might be able to induce vortex ring state. Is this true?

No. More than one criteria must be met to induce VRS, and one is a LOT of
power going into the blades (not being used as it is when pitch is pulled,
but DRIVING the blades when pitch is pulled) and the other is that rapid
descent rate (300fpm typically). If both aren't present, you're not going to
find yourself in the ****.


--
Beav


Please note my E-mail address is "beavis dot original at ntlworld dot com"
(with the obvious changes)

Beavisland now lives at
www.beavisoriginal.co.uk

You still up and about Beav?

--
Alan

Remove the dots to reply
http://heliweb.users.btopenworld.com/


"Beav" wrote in message
...

"Greg Johnson" wrote in message
m...
It it possible to get into vortex ring state (or settling with power)
during an autorotation?

No.

A friend at my radio control helicopter field claimed that you shouldn't
do a vertical autorotation, because you might enter vortex ring state
if you do.

He's talking ********. To reach "that" stage, the air must be travelling
DOWNWARDS through the rotors. In autorotaion, the air is travelling
UPWARDS
and turning the blade. (Well the AIRFLOW is upwards due to the downwards
trajectory of the heli)

This doesn't seem right to me based on my limited knowledge of the
aerodynamics of helicopters.

You're right, its not right.

Clearly, during an autorotation the main blades are developing lift,
just
like a glider's wings are generating lift when it descends at a constant
velocity.

Exactamundo (almost:-)

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.

Correct.

Furthermore, the inner counter-rotating vortex that develops during
vortex ring state would seem not to be possible during an auto, because
there is no down-wash over the intermediate part of the blades.


Or over any part of the whole machine.

The air
is going up through the rotor disk the whole way out from blade roots
to tips.

Indeed it is, and one day I'll read the whole bleeding post before I start
typing :-))) save myself a lot of work if I did:-)


(This is all just seat-of-pants intuition; I hope someone with
aerodynamic
knowledge can say if my intuition is right, and what the aerodynamics
of an auto are, and why in that regime settling with power can't
happen.)

The seat of your pants is working well from where it's sitting:-)

The one place I can (just barely) imagine it might be possible is during
the brief moment at the bottom of an auto when you crank up the
collective
to exchange rotational inertia for lift to cushion your landing.

Not going to happen there either. You need to have POWER into the blades
(and lot of it) plus a descent rate exceeding 300fpm.

At that
point it seems like you are adding energy to the rotor head other than
that which is coming from the descent through the air.

Actually, you're USING the energy already stored, so you're losing energy
not adding to it.

My supposition
is that you can turn the blades using the engine, or you can turn
the blades using the stored rotational inertia in the blades, and in
either case you might be able to induce vortex ring state. Is this
true?

No. More than one criteria must be met to induce VRS, and one is a LOT of
power going into the blades (not being used as it is when pitch is pulled,
but DRIVING the blades when pitch is pulled) and the other is that rapid
descent rate (300fpm typically). If both aren't present, you're not going
to
find yourself in the ****.


--
Beav


Please note my E-mail address is "beavis dot original at ntlworld dot com"
(with the obvious changes)

Beavisland now lives at
www.beavisoriginal.co.uk

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.

"Alan" wrote in message
...
You still up and about Beav?

I was, and then I went to bed, but I got up again this morning and went out.
I got back though and here I am, sitting here with a cuppa in my hand
thinking about getting out of this chair and transfering to another where
can have a drag. Good thnking that.... Gone-)


--
Beav


Please note my E-mail address is "beavis dot original at ntlworld dot com"
(with the obvious changes)

Beavisland now lives at
www.beavisoriginal.co.uk

Hi Kevin,

Glad to know it's not just "me!" ;-)

Actually, from what I've read through the years, even the guys out there
with full blown PhD's in rotorcraft aerodynamics don't fully understand this
stuff so us little peons shouldn't be too embarrassed by the confusion we
feel when trying to get a handle on it.

Fly Safe & Keep the training reports coming! :-)
Steve R.

"The OTHER Kevin in San Diego" skiddz *AT* adelphia *DOT* net wrote in
message ...

This very thing is really irritating to me as I study. Different
books state different things and my GS instructor says yet another
thing. The books I primarily refer to are Principles of Helicopter
Flight and Rotorcraft Flying Handbook. Another source is a web site
who's URL escapes me at the moment. Something like
dynamicaviation.com.. (really good diagrams of things like transverse
flow, disymmetry of lift etc..) The one thing I've discovered as I
study it that no two books agree on any point. It's kinda like
extrapolating max manifold pressures for given temps and DAs off the
placard in the helicopter. That's why when I answer quiz/test
questions, I preface a lot of "specific" numbers with the word
"approximately"

Steve R. wrote:

Actually, from what I've read through the years, even the guys out there
with full blown PhD's in rotorcraft aerodynamics don't fully understand this
stuff so us little peons shouldn't be too embarrassed by the confusion we
feel when trying to get a handle on it.

That much is true. Anyway, you're not going to enter VRS in an auto.
No power, no VRS.

And the problem with a vertical autorotation from altitude to the ground
isn't maintaining rotor inertia - you'll have plenty of that.

-Ryan
ATP, CFI (airplanes and helicopters)

"Steve R." wrote in message
...
Hi Kevin,

Glad to know it's not just "me!" ;-)

Actually, from what I've read through the years, even the guys out there
with full blown PhD's in rotorcraft aerodynamics don't fully understand
this
stuff so us little peons shouldn't be too embarrassed by the confusion we
feel when trying to get a handle on it.

So HOW do these things get off the ground? Are they sucked off (PuLEASE!!
or are they blown off?


--
Beav


Please note my E-mail address is "beavis dot original at ntlworld dot com"
(with the obvious changes)

Beavisland now lives at
www.beavisoriginal.co.uk

"Beav" wrote in
:


"Steve R." wrote in message
...
Hi Kevin,

Glad to know it's not just "me!" ;-)

Actually, from what I've read through the years, even the guys out
there with full blown PhD's in rotorcraft aerodynamics don't fully
understand
this
stuff so us little peons shouldn't be too embarrassed by the
confusion we feel when trying to get a handle on it.

So HOW do these things get off the ground? Are they sucked off
(PuLEASE!! or are they blown off?



Flight (and many other things in our Universe) make use of measurable
and repeatable forces and effects. However, because we can measure a
force, it doesn't necessarily mean we know why the force is present or
the effect occurs.

For example, you can measure how long you're on the Internet with a
watch, but I doubt you know exactly how the internet is operating while
you're online. Jsut because you don't know, doesn't mean you can't get a
computer and get online though.

Back to flight - gravity is of course a major force, but the collected
scientific knowledge of our species still cannot say exactly what
gravity *is* - we know there is a force, we can measure it and predict
its effects and make use of it, but we still don't know what it is that
causes the force we know as gravity.

Same is true for many physical properties of the universe, that's what
people like Stephen Hawking are trying to find out - they're looking for
a unified theory that will explain what we can measure physically
(gravity, lift, drag etc) and what we have observed about atomic
structure and behaviour (unfortunately Newtonian physics that we use to
achieve flight, don't work at the atomic level). That work continues...

So the ability for aircraft to fly simply proves that we can measure and
make use of forces - not that we understand why those forces exist or
even how they work under all circumstances. For all we know, aircraft
may well be sucked and blown off to achieve flight, personally I'd
rather know the best way for a pilot to achieve those things

toady.

"Toad-Man" wrote in message
...
"Beav" wrote in
:


"Steve R." wrote in message
...
Hi Kevin,

Glad to know it's not just "me!" ;-)

Actually, from what I've read through the years, even the guys out
there with full blown PhD's in rotorcraft aerodynamics don't fully
understand
this
stuff so us little peons shouldn't be too embarrassed by the
confusion we feel when trying to get a handle on it.

So HOW do these things get off the ground? Are they sucked off
(PuLEASE!! or are they blown off?



Flight (and many other things in our Universe) make use of measurable
and repeatable forces and effects. However, because we can measure a
force, it doesn't necessarily mean we know why the force is present or
the effect occurs.

For example, you can measure how long you're on the Internet with a
watch, but I doubt you know exactly how the internet is operating while
you're online. Jsut because you don't know, doesn't mean you can't get a
computer and get online though.

Back to flight - gravity is of course a major force, but the collected
scientific knowledge of our species still cannot say exactly what
gravity *is* - we know there is a force, we can measure it and predict
its effects and make use of it, but we still don't know what it is that
causes the force we know as gravity.

Same is true for many physical properties of the universe, that's what
people like Stephen Hawking are trying to find out - they're looking for
a unified theory that will explain what we can measure physically
(gravity, lift, drag etc) and what we have observed about atomic
structure and behaviour (unfortunately Newtonian physics that we use to
achieve flight, don't work at the atomic level). That work continues...

So the ability for aircraft to fly simply proves that we can measure and
make use of forces - not that we understand why those forces exist or
even how they work under all circumstances. For all we know, aircraft
may well be sucked and blown off to achieve flight, personally I'd
rather know the best way for a pilot to achieve those things

Well that's easy, just lie down (and think of England:-)



--
Beav


Please note my E-mail address is "beavis dot original at ntlworld dot com"
(with the obvious changes)

Beavisland now lives at
www.beavisoriginal.co.uk