Vortex Ring State in gyros?

hismiths

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As a (so far) fixed-wing pilot, I was unaware of this phenomenon until reading about it in the current AOPA Pilot magazine (Feb. 20, pg 78).

Are non-powered rotor wings also susceptible to VRS (aka 'Power Settling)? It would seem so from reading the article.

If so, VRS may be the cause of some of the "How did that happen?" landing incidents I've read about on this forum.

I highly recommend the article.
 

Ed L

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In a word, no.

Great article.

I’m not a helo pilot but got some of my gyro training by one. VRS requires air going down from the rotor as opposed to the air going up (autorotation) in gyros.

In the article there were three requirements: descending at at least 300fpm (possible for gyros), be moving forward slower than effective translational lift (can happen for gyros) AND the disk must be using at least 20% of available engine power (not at all possible - well, MAYBE in some if the prerotator is used IN FLIGHT - but let’s be real...).

The core reason, though, is that it doesn’t happen in autorotation and gyros are always in autorotation.
 

WaspAir

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At a conference held at Hofstra University (Bruce Charnov organized it) some years back, Martin Hollman asserted that it was possible. I was sitting with Ray Prouty (the helicopter aerodynamics author) and another instructor friend, and we all sat there with jaws dropped, looking at each other in disbelief at what we had heard. You may hear others mention it from time to time, but discount it immediately as ill-informed.
 

thomasant

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I understand that gyros are always in autorotation. However, there is a phenomenon of airflow reversal of some sort that happens when the rotor overspeeds and acts like an engine drive for a short period. This is explained very well by Doug Riley and Birdy in a thread in 2014. The phenomenon is not ever described as vortex ring, but the ROD goes incredibly high for a short period.
Unfortunately for me, I was unaware of this condition and I believe my crash on Dec 15, 2019 was probably caused by this phenomenon, as I was literally slammed down to the ground without being able to power out.
The experience that I had was just as Doug Riley explains it in that thread. I regard him as one of the best instructors on this forum by the way he explains things.
 

Jean Claude

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What is ROD? Thank you
 

C. Beaty

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A helicopter hovering out of ground effect can generate what would amount to a giant smoke ring surrounding the rotor, if visible. The air being pumped down by the rotor circulates around this invisible smoke ring, re-enters the top of the rotor and keeps going in a giant circle.

When this happens, the helicopter is basically falling at a very rate of descent; adding more power makes it worse.

The only way of escaping is to gain some horizontal motion.

Can’t happen with a gyro.
 

thomasant

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Not so sure about that. Out of ground effect hover does not recirculate the air again. If sufficient power is available, it is possible to climb vertically from a hover out of ground effect. Done it a lot during my helo flying days.
Vortex ring effect has the descent already established, and further power application only increases the ROD.
A gyro cannot hover in still air.
Chuck has described a phenomenon called "helicoptering" in a gyro in another thread. Can you please explain that "helicoptering" phenomenon again in a little more detail.
 

C. Beaty

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A gyro with a high inertia rotor can enter a tight turn to load up the rotor and gain some excess rpm and then use the extra rpm to play helicopter for a few seconds.

My experience was mainly through the use of tip weighted Hughes helicopter rotor blades: during a landing, I’d roll into a tight turn a few feet above the surface, roll out at nearly zero airspeed and hover while using up the excess rotor speed. The gyro would hang motionless for a few seconds, then would slowly sink to the surface with negligible impact.

Contrary to common belief, high inertia rotors don’t cushion a landing during a normal landing approach; high inertia rotors accelerate more slowly than low inertia rotors and will thump in unless the landing approach is modified to produce some acceleration of the rotor. Without collective pitch control, extra lift requires extra rpm.

This misconception originated from the behavior of Skywheels rotors; the tail heaviness introduces a bit of collective pitch via blade twist during the flare, causing behavior just the opposite of “high inertia.”
 

C. Beaty

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Not so sure about that. Out of ground effect hover does not recirculate the air again. If sufficient power is available, it is possible to climb vertically from a hover out of ground effect. Done it a lot during my helo flying days.
Vortex ring effect has the descent already established, and further power application only increases the ROD.
A gyro cannot hover in still air.
Chuck has described a phenomenon called "helicoptering" in a gyro in another thread. Can you please explain that "helicoptering" phenomenon again in a little more detail.
I agree; the helicopter must be descending vertically to get the vortex ring started.
 

thomasant

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So where is the airflow to the rotors coming from when the short period of helicoptering is being experienced? The fact that it is able to hover against all accepted norms about a gyro not being able to hover is where the conundrum comes in. Is there now a short period of "in ground effect" with reversed airflow taking place?
That is exactly what Doug Riley described about the reversed airflow in a thread.
 

C. Beaty

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Rotor overspeed accelerates more air downward. The extra energy stored in the rotor is no different than power supplied by the engine.

The same principle that extra rotor rpm generated by the landing flare cushions the landing.

And sure, rotor overspeed after the extra load is removed reverses airflow.

I’m sure that you’ve observed that right after landing when the load is removed that a gyro can be backed up using stored rotor energy due to the reversed airflow.

Years ago, Gary Yanson, for a grand finale, would go to 1,000 feet, switch off the engine do his dipsy doodle sequence, land near his gyro trailer and back up to his loading ramps.
 
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All_In

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At a conference held at Hofstra University (Bruce Charnov organized it) some years back, Martin Hollman asserted that it was possible. I was sitting with Ray Prouty (the helicopter aerodynamics author) and another instructor friend, and we all sat there with jaws dropped, looking at each other in disbelief at what we had heard. You may hear others mention it from time to time, but discount it immediately as ill-informed.
It drove Bruce nuts the Hollman never did understand why it cannot happen without power. Bruce Charnov writes about in one of his books and in PRA history he's given us too.
 

thomasant

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So according to the above, there is a form of "engine power" similar to an engine drive that is being produced by the over speeding rotors.

Now here's the quote from Doug Riley from the thread "What is Drag Over?"
A gyro can work like a helicopter for short periods of time. If RRPM is increased above cruising level, the stored energy in the rotor substitutes temporarily for an engine drive. This means that the gyro can stand still in the air, drawing air down through its rotor in a way that is inconsistent with autorotation.

But this can't last long. As RRPM decays, the gyro will settle. Specifically, it will settle into its own downwash. That is, the rotor settles into (1) disturbed air that (2) is already travelling downward.

Just like a helicopter in a similar situation, the gyro will descend vertically very fast and can get buffeted on the way down by the turbulent air of its own downwash.

If you have altitude, you'll recover from this predicament by nosing down and flying out of it.

If you are at, say, 20 feet, though, things will not go well for you. You will pancake in at greater than normal vertical-descent speed. Splat.
The above seems to be a description that is consistent with "settling with power", also termed a vortex ring.
 

C. Beaty

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It drove Bruce nuts the Hollman never did understand why it cannot happen without power. Bruce Charnov writes about in one of his books and in PRA history he's given us too.
Martin Hollman’s father, Dr. Hans Hollman was a well known German physicist who did some pioneering work on magnetrons in the 1930s. Without magnetrons, there would be no microwave ovens and how would we heat our instant coffee?

Martin, just an ordinary square headed German, was living in the shadow of his famous father: that was part of his problem.

Martin received his aeronautical engineering from UCF in Orlando while employed by Martin Aircraft.

Martin and I remained on speaking terms despite his harebrained ideas; I mostly ignored them.
 

wolfy

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So according to the above, there is a form of "engine power" similar to an engine drive that is being produced by the over speeding rotors.

Now here's the quote from Doug Riley from the thread "What is Drag Over?"


The above seems to be a description that is consistent with "settling with power", also termed a vortex ring.
Settling with power and vortex ring state are two different things, but often confused for the same thing.
Basically settling with power could happen when hot heavy and high, you could literally run out of power to hover after coming out of translational lift.
Vortex ring could happen after that if the ROD becomes greater than about 300fpm.

wolfy
 

thomasant

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The two often confused terms are power settling and settling with power
 
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