In a thread below about VRS, there seems to be some confusion about the effects of a tailwind versus a headwind when practicing VRS recognition/recovery. Some pilot/instructors I've flown with like to start the demonstration into the wind. But in that case, when you're in a hover, your downwash is being blown behind you, which makes it difficult to descend into the column of air being produced by your rotor, especially if you're moving forwad even slightly. Thus, it's harder (if not impossible) to get the ship into true VRS with a headwind. Very steep, very slow approaches are perfectly(?) safe if they're performed into the wind. As long as there is some lateral movement of air through the disk, you're good. (SWP at the bottom though? That's another story.)

If you start your VRS demonstration downwind, then your downwash will be blown along with you as you descend on your theoretical messed-up approach (isn't that what we're really practicing here?). Now it's easy to get into VRS! Anybody who has gotten a helicopter into actual, full-blown VRS knows what a wild ride it can be. And now we've had two helicopters (that R-44 and this EMS ship) that have both - apparently - come to grief while practicing VRS maneuvers. Maybe it's time we stop it?

The simplest way to demo VRS is to be straight and level at roughly max endurance airspeed and power setting.  Leave the collective there and pitch up a few degrees and just wait.  You may climb a little, and then descend a little, but maintain that attitude as airspeed bleeds off.  It doesn't seem like much should happen, but every helicopter will walk into VRS this way as it slides further off the backside of the power curve.  Some helicopters enter VRS very smoothly and give very little indication aside from altimeter/VSI.

Headwind/tailwind doesn't matter for the demo because you're not maneuvering based on ground references.  But yes, trying to land w/ a tailwind using the same sight picture as headwind/no-wind approaches while ignoring/forgetting airspeed and rate of descent can easily send you toward VRS.

https://youtu.be/mP72wdgq5PU?t=61

Tailwind only affects sight picture. It has no direct effect on VRS. 

I'll give my take on this, but I'm not going to ride the VRS/SWP merry-go-round.  You guys can decide for yourselves which term doesn't wad your panties.

VRS and SWP are synonymous terms for the aerodynamic condition of a helicopter's powered rotor system generating so much induced flow that it exceeds the lift it provides, resulting in a descent.  Reference your favorite textbook for more precise wording.  https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook/hfh_ch11.pdf

This is distinct from the simpler physics equation of power required vs. power provided.  You are correct that the VRS demo method I described begins as such a situation.  Max endurance power and airspeed means you are using as little power as possible to maintain straight and level.  So when you bring the nose up and begin to decelerate, the same power setting will be inadequate to maintain altitude.  But if you maintain that pitch attitude and power setting, the aerodynamic condition of VRS/SWP will begin to occur (in any helicopter).  I like it because it's eye-opening to realize that, despite the alarming rate of descent that develops, it is often not a dramatic or violent seat-of-the-pants feeling.  You either need to notice the altimeter/VSI, or ground rush (yikes) to notice it.  Beware target fixation, task saturation, etc.

The demo technique is simple, repeatable, and the real thing, making it good for instructing and learning.  Give yourself plenty of altitude on entry and knock it off with plenty to spare or whenever you need more than small cyclic movements to maintain that attitude.  The point is to notice the earlier cues (or lack thereof) and recover appropriately, not to see how extreme it can get.

In the video, sure downwind but, why the change in engine noise and low rotor? 

It wasn't VRS. Downwind, probably high and heavy. More than likely, LTE due to loss of RPM from a stuggling engine...... Ala, if you're going to post a video, make sure it's on topic.....

How do you know it was downwind?

How do you know it was high?

How heavy was it?

What did LTE just prior to hitting the ground have to do with the uncontrolled descent?

This video shows what happens when a pilot fails to recover from VRS and pulls an armpit of collective. Descent rate is not arrested, rotor droop, LTE.

The trim string makes it OBVIOUS the wind was other than off the nose.....

The word "PROBABLY" OBVIOUSLY means something..... 

Hawaiian tours are OBVIOUSLY heavy...... The LZ is OBVIOUSLY other than a hard flat surface, like a mountain..... Hawaii is OBVIOUSLY hot and humid...... 

OBVIOUSLY, other factors played a roll in this incident. Not just VRS.... Therefore, OBVIOUSLY, a poor example...

Are you hallucinating? No one said VRS was the only factor.

You still have no idea how high or heavy it was. The trim string does not represent the airflow experienced by the rotor system, especially during a low speed descent. But "obviously" you knew that.

Or maybe you're just too easily triggered to have adult conversations. Before you switch to 100% all caps, try this:

You're obviously really good with the memes..... Like a 13 year old.....

I don't know why that upsets you so much, but try to be more mature about it. This is not how Captain Obvious should behave.

I always thought the problem was not been able top get out of the descending air before you reach the surface, not part are falling off also. How come?

To expand a little on my initial post... SWP and VRS are different. VRS is *always* SWP, but the reverse is not always true. By definition, Vortex Ring State is when your rotor is re-ingesting its own downwash - I think Olderndirt called it "cavitating," which is close enough. That's not necessarily the case with SWP, which may just be that more power is requied than is available (from either the engine *or* the rotor). For example, let's say that you're heavy on a high-DA, relatively calm day - if you come in with a little too much vertical speed you might not have enough "oomph" in the rotor system to stop the descent. The ship settles right through your ground cushion and you end up with smiling skids and a frowning owner. Sorry, this was not a VRS encounter, so don't blame it on that, Robbie boys!

For VRS to occur, you not only have to be below ETL, but the hovering helicopter has to be stationary over the column of air it is producing. *ANY* lateral movement of the aircraft or that downwash will inhibit or cancel out that re-ingestion. This is why Claude's method works so well - use the tail rotor thrust to "blow" the helicopter sideways and out into clean air. You don't even have to get the rotor up through ETL again - just get it moving (sideways, in this case) with respect to your downwash. Claude may not have invented this manuever or the technique, but at least he showed us how easy it is to get *out* of VRS if you're dumb enough to get into it in the first place.

In a steep, slow, *downwind* approach in which the wind velocity matches your forward speed, you won't be outrunning your downwash. Do the same approach into even a light wind and your downwash will be left behind and voila! (as Claude would say) no VRS. So yes, wind *is* important when it comes to getting into ...and out of...VRS.  With SWP or VRS, since they usually happen at the bottom of messed-up approaches, by the time you recognize that you're getting into it, it's probably too late.

Meaning Ground speed? Or, are you meaning forward speed meaning airspeed as read by the airspeed indicator?

speed with respect to aerodynamics is always airspeed.  Ground speed is not relevant to the conversation. 

nothing else.

I am puzzled by some of you guys who are fixated on groundspeed.  As someone else pointed out, groundspeed has nothing to do with VRS.  The *only* thing that matters is the aircraft's position relative to its downwash.  The helicopter can be stationary, like in an OGE hover, and the downwash can get moved by the wind.  Or, the helicopter can be moving, and its downwash will move in the opposite direction. Either way, you won't get re-ingestion/recirculation.

To get recirculation, the helicopter must be right "over" its own downwash.  As I pointed out, this can happen on a slow, steep, downwind appoach, where the tailwind keeps the downwash right under the rotor. Is this really so hard to visualize?

Aeronautical effect on VRS/SWP. All they do is increase closure rate from a normal sight picture of no wind, or headwind. They only lure you into getting slow enough to settle into your own downwash. They do not as some people are trying to insinuate "blow your downwash underneath you.