reported On Vortex Ring State from active Mi-8 instructor

[admiki]

@cw4ogdenin the video you posted  approach is made with tailwind. Look at smoke direction after the crash.

But if real life pilots say that DCS Mi8 VRS way too easy, I'm going to bow out to their experience.

Edited May 27, 2021 by admiki

[Moriarty]

Chief, good thread. Wouldn’t it be disappointing for a flight sim enthusiast to learn everything they worked hard at for however long was in pursuit of mastering dynamics that are, well, wrong? There might be more than a couple of social science PhDs’ worth of cognitive dissonance buried around here, waiting to be mined. Bringing up VRS is like bringing up pitch in the 109. I’m surprised you haven’t gotten more than 4 pages of feedback just for suggesting it.

[cw4ogden]

37 minutes ago, Moriarty said:

Chief, good thread. Wouldn’t it be disappointing for a flight sim enthusiast to learn everything they worked hard at for however long was in pursuit of mastering dynamics that are, well, wrong? There might be more than a couple of social science PhDs’ worth of cognitive dissonance buried around here, waiting to be mined. Bringing up VRS is like bringing up pitch in the 109. I’m surprised you haven’t gotten more than 4 pages of feedback just for suggesting it.

Thanks for the vote of support.  I mainly just wanted it relooked.  My case is almost entirely circumstantial.  It may very well be realistic that the Mi-8 rides a lot closer to the VRS flight envelope than my frame of reference, but there's not much evidence that's the case, and a fair amount it indicating it behaves much the same as any similar helo.

  So, hopefully this means mission achieved.  I took it on knowing it was already a severely beaten horse, so just hearing they will revisit it as a pretty big win, in my opinion.   

[cw4ogden]

2 hours ago, admiki said:

@cw4ogdenin the video you posted  approach is made with tailwind. Look at smoke direction after the crash.

But if real life pilots say that DCS Mi8 VRS way too easy, I'm going to bow out to their experience.

 

Good eye.  I looked for wind cue on the approach but didn't see any.  That's probably why they want a track file instead of video so they can see the exact parameters.

[Mordants]

@cw4ogden This is top notch stuff, glad I stumbled across it. I love flying the Mi-8 in DCS and although I have a few hours in it I do get caught out from time to time. Let's hope it gets fixed and hopefully isn't a similar problem in the new forthcoming Hind.

[cw4ogden]

5 hours ago, Mordants said:

@cw4ogden This is top notch stuff, glad I stumbled across it. I love flying the Mi-8 in DCS and although I have a few hours in it I do get caught out from time to time. Let's hope it gets fixed and hopefully isn't a similar problem in the new forthcoming Hind.

That’s also an excellent point.  The hip certainly isn’t the latest hot module, but it’s fan base is large.  
 

But the hind is going to be the biggest helo release, to date I would assume.   And therefore an excellent time to throw one stone at two birds.

 

I appreciate the feedback.  And I’m not dying on the hill of it being incorrect, so much as warranting a relook.

 

The community is divided hotly divided, that should be enough to investigate.  And as you mention, because the Hind may be similarly modeled.

Edited May 27, 2021 by cw4ogden

[NineLine]

I have passed this along to the team, we will either hear it needs a fix or they will explain something we might be missing. Thanks for all the input on this.

[Ridder]

On 5/26/2021 at 6:12 PM, cw4ogden said:

 

12:40 seconds:  There is no way that flight profile should result in a VRS accident.  The Vortices would be shed because he is not descending into them.
 

 

 

Really interesting thread. Looking at your flight profile before the mishap, you have an airspeed of less than 5 kmp (2.7 knots) and go from at least 3m/s (590 fpm) vertical to 4 m/s (789 fpm) in the second before really dropping out of the sky. Is that really considered a safe flight profile? I'm not trying to counter your point, I'm legitimately asking as an armchair rotorhead.

 

I'm not a real world pilot and mostly fly the Huey, but recently started the Mi-8 and taking into the account the different units (metric is actually more familiar to me) I had zero issues landing the Hip, which honestly surprised me as I had read so many horror stories. That may well be the result from biased training which is limited to DCS practice, books and ground school instruction by real world pilot, but still with an eye on playing DCS. This has resulted in me coming in to land at a shallower angle probably, I don't know.

[Fri13]

On 5/27/2021 at 3:33 AM, admiki said:

@cw4ogdenin the video you posted  approach is made with tailwind. Look at smoke direction after the crash.

But if real life pilots say that DCS Mi8 VRS way too easy, I'm going to bow out to their experience.

 

I have started to fly Mi-8 again after long time for fighters for preparation of Mi-24. 

And there are few things that made me wonder that VRS is not suppose to be so easily achieved, based to multiple pilots here as well. 

[cw4ogden]

3 hours ago, Ridder said:

 

Really interesting thread. Looking at your flight profile before the mishap, you have an airspeed of less than 5 kmp (2.7 knots) and go from at least 3m/s (590 fpm) vertical to 4 m/s (789 fpm) in the second before really dropping out of the sky. Is that really considered a safe flight profile? I'm not trying to counter your point, I'm legitimately asking as an armchair rotorhead.

 

I'm not a real world pilot and mostly fly the Huey, but recently started the Mi-8 and taking into the account the different units (metric is actually more familiar to me) I had zero issues landing the Hip, which honestly surprised me as I had read so many horror stories. That may well be the result from biased training which is limited to DCS practice, books and ground school instruction by real world pilot, but still with an eye on playing DCS. This has resulted in me coming in to land at a shallower angle probably, I don't know.

I had a hard time getting a track file that was a good example.  I don't know if that means I've learned the quirks of the flight model, or if what I am trying to shed light on is subtle. 

The two I provided aren't smoking guns, per se.  But they illustrate, to me, especially if you look at an external view from the side, that the incipient phase is starting somewhere above 30 knots or so.  If you watch, try to visualize "where is the downwash?"  

The thing illustrated by the track file is the phenomenon is occurring, or at least beginning to occur in phases of flight where the downwash would be well behind the aircraft.  That's what I meant by use the external view.  Does the flight profile look like it would be regurgitating air?  Or would it be getting fresh bites on every pass?
 

At the point in the track file where the aircraft starts to drop like a rock, the bird is solidly in the VRS danger range.  The approach angle goes from below that critical 30 or so degree angle to 40 or 50 degrees.  But VRS seems to be what's sucking the bird into that 40 degree approach angle range.  And I think that is where the problem lies.  

So, I guess I'm saying what feels wrong isn't so much the modeling of the phenomenon, but where it starts to kick in.  To me it feels like it's kicking in too early.  

I marked up a VRS diagram to illustrate my hypothesis.  It's obviously not meant to be spot on accurate, but show graphically what I think is going on.  

The blue line stretching to encompass about where we see VRS starting to occur, currently in DCS.  And in the track file you can see the bird is exhibiting full blown VRS, i.e. the red circle at about a 40 degree angle.  As shown on the graph, even at a 40 degree angle, you are still only in the light turbulence and thrust variation area of the graph.  Versus DCS mi-8 at around 30 degrees you are flirting with disaster and essentially dead by 40 degrees.

For VRS to happen, you have to be re-ingesting your own downwash, which requires vertical or near vertical descent.  That is the key piece missing.  You can't be in VRS if you are not in the same chunk of air you were a half a second ago.  You need to be going almost straight down.  You have to be descending into your own column of air, and that just doesn't happen with any significant forward airspeed, or sideward or rearward for that matter.  

Additionally, related to the graph, it feels like the red area of the graph is much bigger in DCS and the yellow area much smaller than depicted.  Meaning the difference between incipient VRS and full blown VRS is razor thin.  That also explains why things go from hunky-dory to FUBAR so quickly in our model.  There is very little yellow area in DCS in my estimation.

 

4 hours ago, NineLine said:

I have passed this along to the team, we will either hear it needs a fix or they will explain something we might be missing. Thanks for all the input on this.

Thanks to you and the team as well.  

Edited May 28, 2021 by cw4ogden

[cw4ogden]

Linked the full video, but this slide is saying essentially what I am saying.  Also where the thirty degree rule of thumb comes from.  Approach angle is the key variable, not any particular rate of decent.   

Unlike the generic VRS diagram, this one shows units, and the airspeed range we are talking about is less than 10 knots or so.

Below a thirty or so degree approach angle, it is physically impossible to be descending in your own downwash, you go forward 2 units for every unit you go down. 

So, as the gentleman points out, you are vulnerable in a very small window.  Too fast rate of descent, but shallow angle is no problem, because by definition that angle means your going horizontally faster than vertically.

  Too steep, also no problem, as long as you descend fast enough, you will hit the windmill brake state - no vortices.  Essentially on a crazy steep approach you are safe from VRS, that is, until you try to arrest your descent.  At which point you will enter VRS but coming up from windmill brake area on the bottom of the graph.

To encounter VRS, the aircraft has to be near stationary with respect to the column of air it's flying in.  That can actually be 20 to 30 knots GROUNDSPEED with a 10 to 20 knot tailwind, but your indicated airspeed is still going to be in that sub 10 knot INDICATED airspeed region, i.e you are not moving with respect to your own column of air. Capitalization is for emphasis on those two words / concepts.

Yes, you can get into VRS with a decent amount of ground speed caused by downwind landing conditions, but the corollary to that, is because of that tail wind, you still have no significant airspeed.  VRS is a near stationary column of air phenomenon.  Or in this example, one where you were descending near vertically, due to that descent being into a moving column of air.

 

It should not be occurring at 30 KIAS and a 30 degree approach angle and no wind, which is what I tried to demonstrate in the track files.

 

 

Edited May 28, 2021 by cw4ogden

[Volator]

@cw4ogden

 

I haven't read through the whole thread, not being an active DCS Mi-8 pilot, but from what I read it appears you definitely got a point there.

 

I think what you have experienced here with the Mi-8 is something that we can see with several DCS modules. Some real aircraft display some certain behaviour, and then the FM developers go and try to simulate it in DCS. So far so good. What I found with some modules however is that this certain behavior is quite exaggerated at times. It appears the FM developers want to make people really notice or feel the special characteristics of an airframe, and they are proud of it of course in being able to demonstrate this in their code, but in doing so they overdo it and thereby get it wrong, so wrong that a real aircraft wouldn't be accepted into service with those extreme characteristics. Sometimes I also think some sim pilots and FM developers think flying in a sim has to feel hard, difficult, otherwise it wouldn't feel real. I disagree with that and think based on my RL (fixed-wing) flying experience flying, controlling an aircraft is quite easy once you learned it. Just like driving a car. First you gotta learn how to do it, but after some time it becomes natural for you.

[cw4ogden]

@Pilot IkeYes, I alluded to something similar up in the post.  It kind of feels like it was exaggerated, either knowingly or not, to ensure the code had the opportunity to be appreciated.  DCS is probably the first to take even take a swing at modeling VRS, and kudos for the vision, let's just see it through to correctly implemented, hopefully.

[sniperwolfpk5]

Sorry I am not an English speaker. I read the thread and I agree with you on the topic of VRS. I don't have any evidence or proof but something is wrong with hip. The DCS MI 8 is very easy to get into VRS

 

Other than the VRS issue it is one of the best module and Heli Sim available in the market.

[Rogue Trooper]

With the Sim shaker Jet seat it is difficult to drop into VRS in the MI-8, it is a little like flying by the seat of your pants you could say.

 

There are a few videos online of the MI-8 dropping into VRS IRL with catastrophic consequences. She seems to drop into VRS very smoothly.

 

 

 

 

 

[cw4ogden]

47 minutes ago, Rogue Trooper said:

With the Sim shaker Jet seat it is difficult to drop into VRS in the MI-8, it is a little like flying by the seat of your pants you could say.

 

There are a few videos online of the MI-8 dropping into VRS IRL with catastrophic consequences. She seems to drop into VRS very smoothly.

 

 

 

 

 

I've watched them.  I posted about them up there somewhere but my take from the videos is this:

 

Both accidents I reviewed the helicopter was near stationary at a high hover and induced too high a sink rate.  That's fine, the game should model that, and it does, well.

Both pilot's only corrective actions appears to be pulling more collective.  Meaning both pilot's crashed not knowing why the hell they even crashed.  That's not uncommon.  Failure to identify the emergency procedure is linked to a lot of accidents.  But it indicates, at a minimum, they were poorly trained on vortex ring state.  Or they were extremely un-proficient in recovery technique.  

That tells us something.  Specifically, it tells us VRS is a relatively unknown phenomenon in real life in the Mi-8, just like every other helicopter.  Two accidents for an aircraft with a service record and fielding level that is unmatched globally.  

VRS is an aerodynamic phenomenon common to all helicopters.  It doesn't differ drastically with the weight, the number of rotor blades, or various factors.  If anything, the larger the helicopter, the larger the induced flow required to stay aloft, and thus the harder it will be to get into VRS.  VRS is about upflow through the rotors.  It about when you are operating in a column of vertical air.  Due to being stationary and descending or descending with forward speed and a tailwind.
 

What is modelled incorrectly, in my opinion is the ability to encounter VRS on approaches to land.  You just can't.  Not in any helicopter.  You can't get into VRS while you are outrunning your own down wash because it is that downwash being pushed back up into the rotor system that is responsible for the phenomenon. 

When you try to demonstrate VRS to a student, it is NOT easy.  You have to hunt for that one special spot where you are travelling along with your own downwake.  Then you have to stay in it, then you have to push the down stick too far down.  

A VRS accident's parralel in a fixed wing, is a power on stall and spin accident.  Unless you just didn't learnt to fly, or you did, but you just got really careless, it's never ever ever going to be a problem.

 

If I have to go straight down, or almost straight down.  Yes, eyes get riveted to the vertical speed guage.  And for good reason.  I'm not downplaying VRS, but some perspective, people.

VSI is not even part of your scan, ever for a normal or even tactical approach.  It would be a deadly distraction, number one.  I'd smack you on your helmet the moment you took your eyes off the objective.  VSI is included in no real life pilot's scan on a VMC approach.  Yet, to fly this bird, all I hear is I'm doing it wrong and all I need to do is focus on the VSI.  

No, you shouldn't have to come up with non-real world procedures to accommodate flight simulator quirks.
 

[Rogue Trooper]

Some videos of the MI-8 are also attempted flare stops.

I find it harder to find videos of other makes of chopper dropping their weight into their own downwake... it just may be a trait of the chopper that you could be unaware of.

 

I need to be really careless and flippant with my approach to even hint at VRS in the DCS MI-8, but again the vibrating jetseat just gives me a nice bit of feedback that aids my glancing of the instruments, especially the vertical velocity indicator.... surely the true god send instrument to the chopper pilot.

 

The MI-8s VVI is very slow to respond in DCS mind.... it is also metric so a small needle deflection down is a whole hunk a drop.

But she is slow to enter VRS and slow to get out, if you get into VRS in the hard flare then go sideways to get out of your down wake, it is simply the fastest way to get that big old girl moving quickly. Trying to pull the nose down to accelerate out of the flare during VRS is simply suicide and just too late in this girl.... she is no R22.

 

The DCS MI-8 is the greatest chopper programmed into any sim.

Edited May 29, 2021 by Rogue Trooper

[cw4ogden]

1 hour ago, Rogue Trooper said:

surely the true god send instrument to the chopper pilot.

 

The MI-8s VVI is very slow to respond in DCS mind.... it is also metric so a small needle deflection down is a whole hunk a drop.

But she is slow to enter VRS and slow to get out, if you get into VRS in the hard flare then go sideways to get out of your down wake, it is simply the fastest way to get that big old girl moving quickly. Trying to pull the nose down to accelerate out of the flare during VRS is simply suicide and just too late in this girl.... she is no R22.

 

The DCS MI-8 is the greatest chopper programmed into any sim.

 

Except it really isn't regarding the VSI.  That was the point.  No one looks at a VSI for normal maneuvers.  That is just how DCS pilot's have learned to modify their behavior to adapt to what in real life, is a relatively benign aerodynamic hazard. 

I don't want to sound flippant, but what you are saying, in a nutshell, is I need more hardware to learn how to fly properly.   And that's just a dumber version of the argument that: I just need to learn how to fly it.  I can fly it, it's not a matter of me being unable to adapt, or needing more hardware.  It's that real life is not being replicated here, and I've stated why.  If you have a counter-argument why the Mi-8 should fall out of the sky where other helos do not, I'm receptive to a productive dialog and evidence supporting the model being correct, it's just that thus far, I haven't seen any, and I've seen plenty of evidence to the contrary.  

In short, I don't know why someone would post arguing against the possibility your sim could be made more true to real life.  I'm not asking them to remove VRS, just revisit it.  See if it might need a tweak.

No amount of "to to fly it this way." is gonna sink in with me, because you're missing my point.  I shouldn't have to stare at my VSI.  It's a DCSism caused by improper modeling of VRS.  

It's an adaptation necessary to fly the computer, and your saying I should change my expectations, or learn to fly computer helicopters.

No!  For the love of God do you people not want those with real world experience to come forward?  Or should I take the advice of many given, and just let you have your broken sim because it isn't worth it fighting with the ED fanboys?


I don't give two craps about it honestly.  But much like a piece of trash laying on the ground, I 'm not that guy that knowingly walks on by and says "not my trash".

This isn't my trash.  But I'll pick it up, if no one else will.

If I'd had a piece in the development we wouldn't be having this discussion, no way I'd let the bug in to begin with.  And if it isn't a bug, no way I'd let my community flounder asking for clarity without providing it.  

Two options are possible:  It's right, and the reams of information surrounding mi-8 flight standardization procedures, and techniques and charts to avoid VRS is just absent from the internet.

 

Or,

 

It's wrong.

 

Edited May 29, 2021 by cw4ogden

[Rogue Trooper]

2 minutes ago, cw4ogden said:

Except it really isn't regarding the VSI.  That was the point.  No one looks at a VSI for normal maneuvers.  That is just how DCS pilot's have learned to modify their behavior to adapt to what in real life, is a relatively benign aerodynamic hazard. 

I don't want to sound flippant, but what you are saying, in a nutshell, is I need more hardware to learn how to fly properly.   And that's just a dumber argument than I just need to learn how to fly it.  I can fly it, it's not a matter of me being unable to adapt, or needing more hardware.  It's that real life is not being replicated here, and I've stated why.  If you have a counter-argument why the Mi-8 should fall out of the sky where other helos do not, I'm receptive to a productive dialog and evidence supporting the model being correct, it's just that thus far, I haven't seen any, and I've seen plenty of evidence to the contrary.  

In short, I don't know why someone would post arguing against the possibility your sim could be made more true to real life.  I'm not asking them to remove VRS, just revisit it.  See if it might need a tweak.

No amount of "to to fly it this way." is gonna sink in with me, because you're missing my point.  I shouldn't have to stare at my VSI.  It's a DCSism caused by improper modeling of VRS.  

It's an adaptation necessary to fly the computer, and your saying I should change my expectations, or learn to fly computer helicopters.

No!  For the love of God do you people not want those with real world experience to come forward?  Or should I take the advice of many given, and just let you have your broken sim because it isn't worth it fighting with the ED fanboys?


I don't give two craps about it honestly.  But much like a piece of trash laying on the ground, I 'm not that guy that knowingly walks on by and says "not my trash".

This isn't my trash.  But I'll pick it up, if no one else will.

If I'd had a piece in the development we wouldn't be having this discussion, no way I'd let the bug in to begin with.  And if it isn't a bug, no way I'd let my community flounder asking for clarity without providing it.  

Two options are possible:  It's right, and the reams of information surrounding mi-8 flight standardization procedures, and techniques and charts to avoid VRS is just absent from the internet.

 

Or,

 

It's wrong.

 

 

glance was the word I used I believe....

 

In VR it is more the whole you take in.... very liberating.

[cw4ogden]

1 hour ago, Rogue Trooper said:

The DCS MI-8 is the greatest chopper programmed into any sim.

On this we agree.  It's a great sim.  Best civilian helo sim I've flown by miles and miles.  

But that is all the more reason to make sure VRS isn't the one poorly modeled aspect of the best helo sim.

2 minutes ago, Rogue Trooper said:

glance was the word I used I believe....

 

 

I wasn't intending to quote you.  Early on, up in the thread, the discussion turned to the VSI and I was told to "stare" at it essentially.

[Rogue Trooper]

2 minutes ago, cw4ogden said:

On this we agree.  It's a great sim.  Best civilian helo sim I've flown by miles and miles.  

But that is all the more reason to make sure VRS isn't the one poorly modeled aspect of the best helo sim.

Yes I agree, it is pretty damned good what they have achieved with so little.

Edited May 29, 2021 by Rogue Trooper

[cw4ogden]

14 minutes ago, Rogue Trooper said:

Yes I agree, it is pretty damned good what they have achieved with so little.

 

Don't take me wrong.  This thread is going on two months, now.  I appreciate the back and forth, but it can be aggravating because I have heard all the counter-arguments by this point.  I'd welcome new evidence.  A VRS chart specific to the MI-8 or similar. 

But the discussions tend to devolve into "you don't know how to fly it", while I give out free rotary wind aerodynamics classes that fall on deaf ears. 

 And it sounds like they are doing a re-look.  So mission accomplished, even if they find everything is hunky-dory, as is.  The issue will be put to bed.

What frustrates me, in debating it, is I have a circumstantial case that's pretty solid.  I also have the background to be speaking from experience.  And still that wasn't enough so I phoned a friend who's in the Mi-8 community to see if the hip had any type of restrictions aimed towards VRS, or flight characteristics that would be markedly different than the bird he and I both flew.  He gave some wiggle room, but the answer was a pretty definitive, "the Mi-8 is not a VRS deathtrap">

That's all I can do.  ED wants to give me an MI-8 and a safety pilot, I'll investigate.  But barring that, it doesn't match what I experienced, and I've trained the maneuver.  There's no evidence it's an abnormal hazard within the hip community on the internet, and my hip pocket source also confirms the Mi-8 handles essentially like any other helo he has flown.  

This should have been relooked just on the circumstantial case alone, and the controversy surrounding it.   It really should have been re-looked when pilot after pilot chimed in and said this feels wrong.  It's gonna get a re-look so I'm fairly happy, even if I end up being full of hot air.

I have no dog in this fight other than flight model accuracy.  

Edited May 29, 2021 by cw4ogden

[Черный Дракул]

14 hours ago, cw4ogden said:

It should not be occurring at 30 KIAS and a 30 degree approach angle and no wind, which is what I tried to demonstrate in the track files.

Not a (heli, too) pilot here, but I know the metric gauges. I can't tell if VRS is modelled correctly or not (my virtual Mi-8MTV2 appears to come from a bad patch, crashing constantly), but please note that VSI is gauged in single meters per second, while speed is in kilometers per hour. The diagram you've provided should read the safe-ish 40° slope at 44 kph speed, hitting the yellow envelope at 2.2m/s (while the commentary is gauged in feet per minute, the scale is titled fpS, which appears to be wrong, so I presume it's in fpm). 

 

The bullseye seems to sit at 700 fpm = 3.5m/s at 8 kias ~= 15 kph

Edited May 29, 2021 by Черный Дракул

[cw4ogden]

27 minutes ago, Черный Дракул said:

Not a heli pilot here, but I know the metric gauges. I can't tell if VRS is modelled correctly or not (my virtual Mi-8MTV2 appears to come from a bad patch, crashing constantly), but please note that VSI is gauged in single meters per second, while speed is in kilometers per hour. The diagram you've provided should read the safe-ish 40° slope at 44 kph speed, hitting the yellow envelope at 2.2m/s (while the commentary is gauged in feet per minute, the scale is titled fpS, which appears to be wrong, so I presume it's in fpm). 

This was one of the first things brought up, early on in the thread.  The VSI being in meters per second.  

It is also anecdotal evidence, but the mere fact there are not aircraft specific charts for each aircraft is evidence as well.  As is the fact the charts have units of measure that not even defined, much less propagated with actual airspeeds and rates of descent tells us VRS is not the hazard DCS mi-8 would lead you to believe it is.

If VRS was as dangerous in real life as in DCS hip, there would be aircraft specific charts.  There would be charts specific to gross weight and specific to altitude and temperature.

 

Here is an example:  We fly close to the edge of the performance envelope for retreating blade stall, anytime we fly at high speeds,  retreating blade stall; not a deadly killer like VRS.

Yet, chart after chart is available to predict at what airspeed I will encounter retreating blade stall.  And if it's cold, I'm more worried about blade compressibility, (a stupid name for rotor going supersonic) I have to compute that number.  Neither will be my death, but I'm required to compute them, nonetheless.

I can't takeoff without computing that number, 15 pages of charts in the -10 and it's not going to kill me.  Yet I don't even have a single chart for VRS in my manual.  I compute no VRS numbers on performance planning worksheet, and if you ask someone for your VRS performance planning numbers they are going to look at you like you have a dick growing out of your forehead.

And all of that is because, as I pointed out up in the thread, VRS is deadly, yes, but it is not common.  You really kind of have to be an jackass, or unaware of the phenomenon, or unaware you are landing with 10+ knots tailwind to get into it.  

I would take as evidence any such chart, but they just don't exist at the pilot level.  Test pilot data, for sure, but not for the pilot, not for the Mi-8, not for any helicopter I know of, because VRS is so easily avoidable.  We derive all sorts of mostly unnecessary trivial numbers prior to a flight, and it's one in a hundred flights you need one of those numbers outside your basics IGE OGE hover power / Go No Go torque, and not a single one of them relates in any capacity to VRS.    

Edited May 29, 2021 by cw4ogden

[cw4ogden]

52 minutes ago, Черный Дракул said:

The bullseye seems to sit at 700 fpm = 3.5m/s at 8 kias ~= 15 kph

The charts are notoriously vague and notoriously non specific to airframe, so I’d take those numbers with a grain of salt.  

I’d guess they interpolated data for whatever helo they teach based on the “1.0” mark you see in most generic VRS diagrams on the speed axis and set it to ETL transition speed, and converted units for rate of descent.  
 

In other words, they tailoring the drawing so the edge of the envelope for VRS is the ETL transition speed of whatever aircraft appropriate to the instruction they give.  Giving their pilots some yardstick to measure where the phenomenon occurs.  And that’s based on the assumption no one is training newbie pilots in a mi-8.  They’re probably dealing with the Robinson or a jet Ranger.
 

Which would indicate the hip probably has a little wider VRS envelope than that diagram.  

 

and I just re-state, the fact that we look at hand drawn diagrams instead of engineering charts with multiple asterisks and a three hour block of instruction on how to use them, the fact we are trying to quantify the units for Pete’s sake with respect to VRS should tell us something.

Edited May 29, 2021 by cw4ogden