cw4ogden

@Wadim Forgive my drawing technique, but this is what I feel is going on. A VRS susceptibility range that is exaggerated. Track file shows aircraft entering VRS from above ETL (which is impossible) at 30 KIAS or about 55 kmph. Aircraft should not be susceptible to VRS, regardless of rate of descent, or approach angle at that speed, as stated earlier. Even the Mi8 flight manual says only below 40 kmph. ETL being defined as operating in clean air. Above ETL, induced flow is behind the aircraft before it can be re-ingested into the rotor system. Being above ETL and getting into VRS should be mutually exclusive. You can't experience both simultaneously; being below ETL is a prerequisite, a requirement for VRS. Or, possibly the problem isn't with VRS at all, but the transition airspeed range for ETL, but something seems off if I can get into VRS at 55 kmph, above ETL in conditions the phenomenon can not exist, due to it's very nature. VRS is re-ingested downwash, and by definition, ETL is when you are free of operating in your downwash. 2.trk

I don't doubt the sincerity of the effort put into the coding. I do question the model itself. Not because you or the team didn't do a good job doing research or gathering data, but because introducing a bug, unintentionally, just isn't as impossible as you want it to seem. #1. I understand you believe it is modelled correctly, and it may very well be. I'm not here to badmouth the development team, but, you've yet to address or acknowledge the discrepancy we found. It's a discrepancy, something to look into. I'm not claiming it is hard and fast proof of a bug. Just asking others to check a quirk that may or may not be responsible for what feels off in the flight model. #2. You'd be better served proving to me the Mi-8 flies like the model does in DCS. In other words, I believe it is within realm of possibilities that the Mi-8 is somehow more susceptible the VRS than other helicopters, but I've seen no evidence of it. My hypothesis is if the Mi-8 were as deadly in regards to VRS as it is modeled in DCS, there would be much more information in the way of charts and performance planning information. You'd need it just to survive. If the real life Mi-8 rides a lot closer to the VRS envelope than my point of reference, in reality, that's acceptable. I want "correct" behavior. I don't want a dumbed down version. I just want it to be accurate. You believe it is; I am not totally convinced. Mainly because I can get into VRS in DCS in situations I don't feel I would in real life. That may be differences in the aerodynamics of the different aircraft, or it is a bug. To me it feels like a bug, because I can get VRS in DCS in conditions I assert you couldn't in real life. I'll add that the modelling of VRS when induced from an OGE hover feels exactly right. What feels off is being able to get into VRS in situations where the downwash would be well behind the aircraft. I can test the data all day long, but I am not an unbiased observer anymore. I believe, maybe not with 99% certainty, but believe there is a decent possibility an error crept into the flight model. So I'm asking others who are not vested in the outcome to test what we found. That's all. I am fine with being proven wrong, I'm not an Mi-8 expert. But if it was my code, my work, I'd want to look into any suggestions I got it wrong. If it was my community to manage, I'd never let that community flop around like a dying fish for years without putting this to bed. It's either based in reality, and I'll take the egg on my face, OR, something is slightly off, in which case a fix would be warranted. I hope you get where I am coming from. Maybe I am beating on a dead horse, but lets make sure the horse is really dead. I don't think the modelling is off by much, I think it needs a tweak, not a complete rework.

As far as the education goes. Yes, U.S. pilots are vocational technically trained. The average U.S. line pilot in command is a very poor study of aerodynamics. The knowledge scales up as you go up the ladder of responsibility, and many also take it up (aerodynamic engineering) pursuing their bachelor degree. Ive also known a lot of very book smart people who couldn’t find their way out of a wet paper bag. And I don’t just mean stupid in general, I mean profoundly stupid in the field they’re supposed to be the expert on.

My qualifications are 20 years US Army helicopter carrier flying CH-47. Not the same, but similar in weight. My source is feedback from a friend who flies both birds and tells me the hip mi-8 does not encounter VRS to any greater extent than the ch-47. I also have first hand experience with VRS that I was not prepared for, so it became very personal to me as a pilot, instructor pilot, and standardization instructor (Instructors who teach and evaluate the junior instructor pilots). but I submit, any actual mi-8 experience you have is a much better yardstick, a better measurement of accuracy. I also submit, circumstantially, the aircraft cannot fly the way it does in real life, the way it does in DCS. The most dangerous part of the VRS envelope cannot be at the ETL transition airspeed, because you are only half in it at best. ETL by definition is no vortices. My experience with VRS is it is confined to nearly vertical approaches, (one of the key four factors required for VRS). if you don't have vertical or near vertical descent - No VRS. Tailwind complicates this, but you must be descending in your own rotorwash for VRS. And I can't descend into what's behind me. You need vertical or near vertical descent. Either as a result of going nearly straight down or coming into land with a tailwind. You must be descending into your own air. But also VRS gets inattentive pilots flying Hover OGE not observing rates of descent, and also happens on rapid decelerations where you essentially tilt your disk into your upflow. Which puts you in the windmill brake / autoratative region of the graph. This is fine until you try to stop using power and essentially come upwards through the VRS graph. From bottom up into VRS. Usual result is a very hard landing. Sometimes damage to landing gear / airframe.

I submit your experience is sufficient to speak on the subject. But I don’t understand your conclusion. Are you dismissing the possibility the flight model could be in error, as not a possibility? it could be the translation, but I didn’t get your intent. All of That said. Thus far all it seems you are arguing only that you have very good credentials, which I do not deny. So I’m asking maybe to summarize what you meant. I don’t see how you can dismiss data without evaluating it, based solely on the certificates hanging on your wall. I do not mean to sound satirical, but I accept your qualifications, what do you make of his data?

It doesn't make sense. By this logic, I can get into a vortex ring state in cruise flight if I descend at a high enough speed. Vortex Ring state only occurs below ETL. The definition of ETL is that you have left your downwash. Impossible VRS above ETL. Below ETL, flushing down can be reinvested in rotors, yes. but the required descent rate must gradually increase from a very high descent rate near ETL to a lower descent rate to a cautious start at zero air ambush. The DCS does not. The most dangerous area for VRS seems to be right in the ETL. At this moment, in flight, the acts mainly on the rear side of the rotor, the induced flux from the front of the disc enters the rear.If you get into VRS by going through ETL and not from OGE hover, the beginning is a very progressive phenomenon. It starts at the rear of the rotor system and moves forward as it decelerates. The front half of the rotor will still have clean air around the ETL, as will most of the rear. And according to every VRS chart I've ever seen, an approach angle of less than thirty degrees keeps you out of the VRS danger zone, regardless of your rate of descent. Also not modeled on the DCS Mi-8. Feel free to check it out, but provided the Gentleman's DATA and mine are confirmed, the flight model contains errors.

This does not seem to make sense. By this logic I can get into Vortex Ring State in cruise flight, if I descend at a fast enough rate. Vortex Ring state only happens below ETL. The definition of ETL is you have left your downwash No VRS possible above ETL. Below ETL, the downwash can be reinvested by the rotors, yes. but the rate of descent required should scale progressively from taking a very high rate of descent near ETL to a lower rate of descent to produce the onset of VRS, at 0 airsieed. DCS does not do this, The most dangerous area for VRS, appears to be right around ETL, and gets more forgiving as you slow down more. At the ETL transition point, the phenomenon is acting mostly on the back side of the rotor, the induced flow from the front of the disk being ingested in the rear. if you get into VRS transitioning through ETL, as opposed to from an OGE hover, The onset is a very progressive phenomenon. It starts at the back of the rotor system and works its way forward as you slow down. The front half of the rotor will still have clean air near ETL, as will most of the back half. And according to every VRS diagram I've ever seen, an approach angle of less than thirty degrees keeps you clear of the VRS hazard area, regardless of your rate of descent. Also not modeled on DCS mi-8. Feel free to test this out, But provided the Gentleman's DATA and mine checks out, The flight model is bugged.

He observed the data. It's from his own flight testing it, and he and I want others to test our findings. That is all. Why does everyone just jump to the conclusion: “He must not know what he's talking about”? And how can you arrive at any conclusion when it's clear from your questions, you don't even know what he is saying? Sorry for the English, but this comes from my thread in the English forums.

This would be the VRS curve for the DCS mi-8 given your data.

Assuming we are not missing something, and if your numbers are correct, something is way off. These numbers would indicate the curve is essentially, backwards, with respect to susceptibility and forward airspeed. I.e. it looks like the numbers are flip-flopped. I would expect just the opposite, with very low susceptibility at 40 kmph, and that susceptibility increasing with decreasing forward airspeed to a high susceptibility before leveling off at 20kph or so. At which point the value remains constant.

This makes theoretical sense. VRS is about UP-flow through the rotor. Heavier aircraft, in general, and heavily loaded aircraft will push more air downward to stay aloft, than their lighter, or lightly loaded counterparts. Heavily loaded aircraft, in theory would be somewhat less likely to encounter it. But also have a much smaller available power margin to power your way out of the early phases. Great work by the way. I don't think my track files found the "smoking gun". But sounds like a good place to start, for sure. Tagging @NineLine (because this may be a new finding and for your track files).

Could you post your track files and any findings here as well? Understand you can't post the source, graphically, it would be something like this? Are there different charts for different configutations, or operating conditions, or just one chart?

I was not aware. Thanks for the information. What is the source document?

Soviet doctrine is going to be written for the Afghanistan theatre. It’s likely never been updated, or at least changed significantly in those updates to address a problem that isn’t killing that many. Wouldn’t be sad if we had 6000 foot hip performance at sea level regarding VRS because somebody misunderstood what the manual meant? What if the entire problem is the fact that it was modeled on the one clause, maybe the only in the MI8 manual that’s written as a rule of thumb for operating at 6000 feet or so? that could explain why it’s always felt like we’re operating at high altitude even near sea level, speaking solely to VRS not performamce. 40 kph is going to be associated with ETL and maybe a small cushion or even rounded up possibly for ease of memory. I don’t know what to make of 6 to 13 degrees approach angles, to associate with anything. I don’t know. It seems an odd range? Am I fine at twenty? it could mean normally, light weight etc angles up to 13 degrees are safe, but decreasing to six as you take on aggravating factors like weight or altitude.

Yes, those numbers seem reasonable the same way 300 feet per minute seems reasonable, as an avoid criteria range, though. Not that it is saying that’s where the phenomenon will start. that has fudge factor built in for any number of things as well. regarding approach angles, we keep talking about it like we can just choose your airspeed, rate of descent and your angle, independent of each other, when you can’t. there’s an airspeed (groundspeed technically) for every approach angle and associated rate of descent. Just clarifying not leveling criticism. I can’t see the video on my phone, but I will watch it and let you know. 6 m/s down is fast. That’s what? 1200 ft / min? I’d have guess 800 -1000 tops feet per minute for an unloaded mi-8. What is forward airspeed, is my question I don’t care about the rate of dissent so much is how fast is he going forward?

And here’s the kicker, what if the mission asked me to fly that profile? What do you tell the boss, No can-do sir, that’s too steep an approach angle? No, you would dig out some charts and figure out exactly how close to that demon you can fly. But you can’t, do that in DCS or real life, because the charts don’t exist, because the whole thing is a phony, at least with regards to the steep but well within a tactical approach style landings. So what does a real life pilot do? You keep your approach angle below 30°, and you avoid going straight down at all costs. But when you do have to go straight down you just do it slowly, using a ruler of them with no more than 300 ft./min., yes I know the gauge is measured in meters per second. I’m sure the Russians have their own with thumb, In the US Army 300 ft./min. is designed to keep you absolutely 100% above the vortex ring envelope. it works in any DA any gross weight combination. It lead to confusion early on in this thread, so, for everyone wondering where the hell 300 ft./min. came from, either with respect to this thread, respect to hearing it used in relation to vortex ring state, that 300 ft./min. comes from the horizontal line, if you drew one up across and intersecting tangent to the top of VRS. You physically cannot be in vortex ring state, in vertical descent at that rate of descent or slower. It works because it’s failsafe. It’s origin is to avoid the need for charts. Or possibly to combat the lack of specific charts. Not because it’s the rate of descent at which VRS is going to start occurring. It’s the rate it can’t occur, basically. And for straight down it’s plenty. It’s slow, but that’s just how you have to do it. You can define straight down as anything beyond that thirty, because it’s going to feel like it. But generally talking vertical descents here. Can you exceed 300 feet per minute? Sure. But at that point, you are now your own test pilot, and you better be prepared to be your own lawyer, because you are in no man’s land my friend. Joe Schuckatelli, pilot extraordinaire, can tell you it is safe at 600 ft./min., But There’s not a chart he can show you to prove it. And it won’t be true for all conditions. That’s where the 300 minute rule of thumb comes from, and explains why there is an entire lack of charts in general regards VRS, They are unnecessary for 99.99% of all flight profiles. ... #1. don’t exceed a 30° approach angle. A standard glide slope is 3 degrees for reference. 30 is your shoes / pedals area. Don’t come in 30 times too steep. #2 If you can’t follow rule one, you must go down slowly. You can Probably go faster than 300 feet Per minute, but why be your own test pilot? Stay in the known safe region, because you don’t know where the drop off is, because no one does. #3 If you Must land with a tailwind, apply both rules #1 and #2. That is everything you need to know about vortex ring state to be a helicopter pilot. if you can say you have diligently followed all three, rules and have never gotten into VRS I salute you! You can get into the vortex rings like state during rapid decelerations as well, but that’s a whole other discussion. It’s essentially coming backwards from the bottom of the chart in a windmill brake state, up through the bottom of the graph, it’s usually transitory and usually results in the ass end falling out. Right before your rotor wash blows past you. That phenomenon has caused countless hard landings, (crashes were no one dies) but that hazard is nowhere near as well flushed out as VRS is. *** for the technically inclined, yes I know a hard landing has a specific meaning, I’m referring to the many Class A mishaps that were labeled “hard landings”, so as not to be alarmist about the accident rate in media coverage.

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.

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.

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.

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. 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.

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.

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.

@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.

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.

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. Thanks to you and the team as well.