cw4ogden

If there is something bites MI-8 pilots in the butt above 50 km/h, if such thing actually even exists, it is not vortex ring state. Or you are doing airshow maneuvers and it serves you right for not understanding the demon you’re playing with. VRS you must be in your own downwash at least long enough for the next blade to pass. Undisturbed air has no induced flow. If every blade is getting it clean bite of air you have no induced flow to act on the rotor system. it is the very reason for the existence of transitional lift benefits. It is why your helicopter goes up faster in forward flight than at a hover. It’s why there is a one to one correlation in the chart, and why the chart doesn’t continue horizontally to these airsspeed you refer to. It has a limit bounded by a horizontal rate of motion. If it did not that circle would extend horizontally the length of the chart. What you are trying to say is there is no upper airspeed limit to which VRS is a threat and that is false. anyone who reads the graph can see that. I think you are letting something theoretical get in the way of how it actually works, or mixing and matching up multiple different phenomenon. it boggles my mind, there is no equivalent term to ETL in your flying culture. But it certainly explains why this phenomenon would be confusing. This is obviously not something well understood by the MI-8 community. It is not something well understood by the US Army either. Most of my career vortex ring state was called settling with power, Which has lead to much confusion over the years. Only in recent years it’s been clarified. So I do know this is not well understood. But having nearly killed me, in my case trying to come to a stop too fast at a landing zone, it is some thing I spent years learning about. The average pilot does not understand VRS, this is true. But this is my personal enemy. I took time to learn the demon.

This is true, but it ignores the fact that certain parameters are required and those parameters are documented in the chart. I can get into the VRS anytime I have a vortex ring state. But a vortex ring state can only develop under certain conditions. You are telling me these conditions exist outside the standard VR as envelope and I see no evidence that is true. Show me a chart with these flight regimes you speak of Where I can be moving horizontally and get into vortex ring state. I will submit you cannot because they do not exist. vortex ring state is a vertical or near vertical descent phenomenon. Or Placing the aircraft in such an unusual attitude, as to affect the same thing.

Vertical speed is the vertical axis of the graph. It is labeled V/V for vertical velocity and has a one to one correlation, as indicated by the two “1.0‘“s . All you need to do is figure out your ETL airspeed and set the horizontal 1.0 at thus speed. The chart is telling you it’s a one to one correlation. There is only one airspeed, approach angle and rate of dissent for any given flight profile, and it can be found on the chart Now convert units to vertical speed. Example: 1 kph = 0.28 m/s if you ETL airspeed is roughly 50kph based on highest estimate I’ve seen. 50 x .28 = 1.0 on the chart. That’s how that works. Now look at the lines I drew because if you understand that you understand what I’m saying. 50 x .28 sets the 1.0 at 14 m/s . That’s fully developed vortex ring state. Middle of the circle labeled 1.0 you can interpolate to approximate where the top edge of the envelope is, by measuring the distance between zero and the top of the VRS envelope, and the 1.0 line. This is why the chart is universal, it is dictated by your particular aircraft’s ETL speed varies only slightly by airframe. if you do not understand the chart you do not understand VRS. I get what you’re saying that theoretically in forward flight This can happen because the rotor is inducing a flow always. And I get that you can put a rotor system into a vortex ring state with unusual maneuvers. But those maneuvers still have to make you descend into your own downwash. Which you physically cannot do it but airspeed above ETL. To go from high speed to descending into one’s own downwash, your velocity vector must move straight below the rotor wash. That can happen in any number of flight angles and approach profiles. But they must conform to the chart. You have to be going down in your own air. this can be caused by the pilot rapid decelerations and standing the aircraft on its tail. But you have put your velocity vector into your down wash. In this case, the deceleration has tilted your rotors upwards into the oncoming flow. in forward flight , Your induced flow has to remain in the area of the rotor system long enough for you to sink into it. And air speeds above about 30 km/h to 40 km/h, your induced flow is well behind the aircraft before it can be ingested into the rotor system again. Everything you need to know is in the chart you refuse to look at.

Look at the two blue lines. If I keep my rate of descent above the horizontal blue line - No VRS is possible. If I keep my approach angle shallower than the blue line - No VRS is possible. If I want to know the airspeed range it occurs, the 1.0 on the bottom of the graph is correlated to ETL. Above 1.0 horizontally also No VRS is possible. This is what I am saying. Everything you need to know is in the graph, if you know what you are looking for and understand the concept of VRS.

No, you just physically can't get VRS in horizontal flight above ETL airspeeds. And no, just no to that last sentence. Show me a cruise flight VRS accident or any VRS accident that caused a structural failure in flight. Ridiculous. If VRS was easy to understand, we wouldn't be having this conversation.

You seem to be mixing rotor tip vortexes with vortex ring state. Not the same thing. One is a normal phenomenon always present, the tip vortices. VRS is an abnormal flow state with vortexes developing inboard due to combination of induced flow and rate of descent. if you look at a VRS diagram you see that both vertical speed and approach angle are critical. Stay below 30 degrees or keep your rate low enough, it should be manifestly impossible to encounter VRS. I think you misunderstand the phenomenon if you are saying it can be encountered in all modes of flight. You can't get into to VRS above ETL because you are not recirculating the same air. That air is behind you before it's induced flow can be a factor. By this logic, if I can get into VRS at any airspeed, why no VRS in cruise flight with collective reduction? You need specific criteria to encounter VRS. In any discussion of VRS, Russian or American, the very first criteria listed is always vertical or near vertical descent. This is a low airspeed phenomenon by its very nature. http://www.svvaul.ru/nashi-resursy/knigi-onlajn/aerodinamika/604-pilotirovanie-vertoljota-na-rezhime-malykh-skorostej#:~:text=Самопроизвольное How do you decrease rotor pitch to a critical angle and achieve a blade stall? This seems to makes no sense.

From the FAA handbook on helicopter flight. Note the passages in BOLD text. Vortex Ring State Vortex ring state (formerly referenced as settling-withpower) describes an aerodynamic condition in which a helicopter may be in a vertical descent with 20 percent up to maximum power applied, and little or no climb performance. The previously used term settling-with-power came from the fact that the helicopter keeps settling even though full engine power is applied. In a normal out-of-ground-effect (OGE) hover, the helicopter is able to remain stationary by propelling a large mass of air down through the main rotor. Some of the air is recirculated near the tips of the blades, curling up from the bottom of the rotor disk and rejoining the air entering the rotor from the top. This phenomenon is common to all airfoils and is known as tip vortices. Tip vortices generate drag and degrade airfoil efficiency. As long as the tip vortices are small, their only effect is a small loss in rotor efficiency. However, when the helicopter begins to descend vertically, it settles into its own downwash, which greatly enlarges the tip vortices. In this vortex ring state, most of the power developed by the engine is wasted in circulating the air in a doughnut pattern around the rotor. In addition, the helicopter may descend at a rate that exceeds the normal downward induced-flow rate of the inner blade sections. As a result, the airflow of the inner blade sections is upward relative to the disk. This produces a secondary vortex ring in addition to the normal tip vortices. The secondary vortex ring is generated about the point on the blade where the airflow changes from up to down. The result is an unsteady turbulent flow over a large area of the disk. Rotor efficiency is lost even though power is still being supplied from the engine. [Figure 11-3] A fully developed vortex ring state is characterized by an unstable condition in which the helicopter experiences uncommanded pitch and roll oscillations, has little or no collective authority, and achieves a descent rate that may approach 6,000 feet per minute (fpm) if allowed to develop. A vortex ring state may be entered during any maneuver that places the main rotor in a condition of descending in a column of disturbed air and low forward airspeed. Airspeeds that are below translational lift airspeeds are within this region of susceptibility to vortex ring state aerodynamics. This condition is sometimes seen during quick-stop type maneuvers or during recovery from autorotation. The following combination of conditions is likely to cause settling in a vortex ring state in any helicopter: 1. A vertical or nearly vertical descent of at least 300 fpm. (Actual critical rate depends on the gross weight, rpm, density altitude, and other pertinent factors.) 2. The rotor disk must be using some of the available engine power (20–100 percent). 3. The horizontal velocity must be slower than effective translational lift. Situations that are conducive to a vortex ring state condition are attempting to hover OGE without maintaining precise altitude control, and approaches, especially steep approaches, with a tailwind component. When recovering from a vortex ring state condition, the pilot tends first to try to stop the descent by increasing collective pitch. However, this only results in increasing the stalled area of the rotor, thereby increasing the rate of descent. Since inboard portions of the blades are stalled, cyclic control may be limited. The traditional recovery is accomplished by increasing airspeed, and/or partially lowering collective to exit the vortex. In most helicopters, lateral cyclic thrust combined with an increase in power and lateral antitorque thrust will produce the quickest exit from the hazard. This technique, known as the Vuichard Recovery (named after the Swiss examiner from the Federal Office of Civil Aviation who developed it) recovers by eliminating the descent rate as opposed to exiting the vortex. If the vortex ring state and the corresponding descent rate is allowed to progress to what is called the windmill brake state, the point where the airflow is completely up through the rotor, the only recovery may be an autorotation. Tandem rotor helicopters should maneuver laterally to achieve clean air in both rotors at the same time. For vortex ring state demonstrations and training in recognition and recovery should be performed from a safe altitude to allow recovery no less than 1000 feet AGL or the manufacturer’s recommended altitude, whichever is higher. To enter the maneuver, come to an OGE hover, maintaining little or no airspeed (any direction), decrease collective to begin a vertical descent, and as the turbulence begins, increase collective. Then allow the sink rate to increase to 300 fpm or more as the attitude is adjusted to obtain airspeed of less than 10 knots. When the aircraft begins to shudder, the application of additional up collective increases the vibration and sink rate. As the power is increased, the rate of sink of the aircraft in the column of air will increase. If altitude is sufficient, some time can be spent in the vortices, to enable the pilot to develop a healthy knowledge of the maneuver. However, helicopter pilots would normally initiate recovery at the first indication of vortex ring state. Recovery should be initiated at the first sign of vortex ring state by applying forward cyclic to increase airspeed and/ or simultaneously reducing collective. The recovery is complete when the aircraft passes through effective translational lift and a normal climb is established. Hence, my point. VRS and flight above ETL are mutually exclusive. Source: https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook/media/hfh_ch11.pdf

From the FAA handbook on helicopter flight. Note the passages in BOLD text. Vortex Ring State Vortex ring state (formerly referenced as settling-withpower) describes an aerodynamic condition in which a helicopter may be in a vertical descent with 20 percent up to maximum power applied, and little or no climb performance. The previously used term settling-with-power came from the fact that the helicopter keeps settling even though full engine power is applied. In a normal out-of-ground-effect (OGE) hover, the helicopter is able to remain stationary by propelling a large mass of air down through the main rotor. Some of the air is recirculated near the tips of the blades, curling up from the bottom of the rotor disk and rejoining the air entering the rotor from the top. This phenomenon is common to all airfoils and is known as tip vortices. Tip vortices generate drag and degrade airfoil efficiency. As long as the tip vortices are small, their only effect is a small loss in rotor efficiency. However, when the helicopter begins to descend vertically, it settles into its own downwash, which greatly enlarges the tip vortices. In this vortex ring state, most of the power developed by the engine is wasted in circulating the air in a doughnut pattern around the rotor. In addition, the helicopter may descend at a rate that exceeds the normal downward induced-flow rate of the inner blade sections. As a result, the airflow of the inner blade sections is upward relative to the disk. This produces a secondary vortex ring in addition to the normal tip vortices. The secondary vortex ring is generated about the point on the blade where the airflow changes from up to down. The result is an unsteady turbulent flow over a large area of the disk. Rotor efficiency is lost even though power is still being supplied from the engine. [Figure 11-3] A fully developed vortex ring state is characterized by an unstable condition in which the helicopter experiences uncommanded pitch and roll oscillations, has little or no collective authority, and achieves a descent rate that may approach 6,000 feet per minute (fpm) if allowed to develop. A vortex ring state may be entered during any maneuver that places the main rotor in a condition of descending in a column of disturbed air and low forward airspeed. Airspeeds that are below effective translational lift (ETL) airspeeds are within this region of susceptibility to vortex ring state aerodynamics. This condition is sometimes seen during quick-stop type maneuvers or during recovery from autorotation. The following combination of conditions is likely to cause settling in a vortex ring state in any helicopter: 1. A vertical or nearly vertical descent of at least 300 fpm. (Actual critical rate depends on the gross weight, rpm, density altitude, and other pertinent factors.) 2. The rotor disk must be using some of the available engine power (20–100 percent). 3. The horizontal velocity must be slower than effective translational lift. Situations that are conducive to a vortex ring state condition are attempting to hover OGE without maintaining precise altitude control, and approaches, especially steep approaches, with a tailwind component. When recovering from a vortex ring state condition, the pilot tends first to try to stop the descent by increasing collective pitch. However, this only results in increasing the stalled area of the rotor, thereby increasing the rate of descent. Since inboard portions of the blades are stalled, cyclic control may be limited. The traditional recovery is accomplished by increasing airspeed, and/or partially lowering collective to exit the vortex. In most helicopters, lateral cyclic thrust combined with an increase in power and lateral antitorque thrust will produce the quickest exit from the hazard. This technique, known as the Vuichard Recovery (named after the Swiss examiner from the Federal Office of Civil Aviation who developed it) recovers by eliminating the descent rate as opposed to exiting the vortex. If the vortex ring state and the corresponding descent rate is allowed to progress to what is called the windmill brake state, the point where the airflow is completely up through the rotor, the only recovery may be an autorotation. Tandem rotor helicopters should maneuver laterally to achieve clean air in both rotors at the same time. For vortex ring state demonstrations and training in recognition and recovery should be performed from a safe altitude to allow recovery no less than 1000 feet AGL or the manufacturer’s recommended altitude, whichever is higher. To enter the maneuver, come to an OGE hover, maintaining little or no airspeed (any direction), decrease collective to begin a vertical descent, and as the turbulence begins, increase collective. Then allow the sink rate to increase to 300 fpm or more as the attitude is adjusted to obtain airspeed of less than 10 knots. When the aircraft begins to shudder, the application of additional up collective increases the vibration and sink rate. As the power is increased, the rate of sink of the aircraft in the column of air will increase. If altitude is sufficient, some time can be spent in the vortices, to enable the pilot to develop a healthy knowledge of the maneuver. However, helicopter pilots would normally initiate recovery at the first indication of vortex ring state. Recovery should be initiated at the first sign of vortex ring state by applying forward cyclic to increase airspeed and/ or simultaneously reducing collective. The recovery is complete when the aircraft passes through effective translational lift and a normal climb is established. Hence, my point. VRS and flight above ETL are mutually exclusive. Source: https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook/media/hfh_ch11.pdf

Yes, that is my beef. It is modeled well when entered from a hover OGE or very steep approach. It's off, if the most dangerous region is near ETL where, by definition, once beyond, you are not subject to vortex buildup. Around ETL I should be very slightly susceptible, and if I do get into it, it's going to produce a rolling moment, initially at least, as the aft portion of the head encounters it first, from induced from of the forward half, which is still in clean air, all offset by 90 degrees. It's conceivable the Mi-8 goes through ETL much higher speed than normal helos, but I find it unlikely, and unsupported in any documentation. But if that is the case, the modeling may be fine. Regardless, that is the crux of my argument, something is wrong regarding VRS kicking in while you have enough forward airspeed and / or shallow enough approach angle that you should be well clear of your downwash. At this point, the flight model is either off, or the hip exhibits behaviors unlike any other rotary wing aircraft flying. And it's totally undocumented and has led to surprisingly few accidents.

There's really only one sticking point here. Can you get into VRS above ETL? That is a simple yes or no answer. If you answer yes, that's a different debate. It would beg the question: "How?" If you answer no, it is incumbent upon you, or ED to see if the flight model is wrong, or if our testing methods are to blame. We did the due diligence. We obtained the data incumbent upon us as required by ED in the form of the track files to submit a bug report. Yet, I can not tell, at this point, if you've even viewed or considered the evidence. You seem to be dismissing it as out of the realm of being possible. To build a cathedral, you need to lay the first stone. And that stone is can you get into VRS at or above ETL? Nothing else contributes to the conversation until you weigh in on that question, and it's ramifications. The ramifications being to explain what's going on in the track files, if it isn't VRS above ETL. Because we have to start with the foundation of being in agreement on the basic facts.

What you are arguing is that because we have one video of a VRS accident, the aircraft is "dangerous" and therefore the flight model is correct. That's some pretty specious reasoning. That video, that accident is not representative of anything I've asserted. I've have stated, induced from an OGE hover, the modeling is great. It reacts just like the video and is everything I would expect from a VRS simulation. But find me a video with an Mi-8 doing 55 kmph and crashing from VRS. That would be useful evidence. This is not. The aircraft should do exactly what it did in that video and it does in DCS. It just also does a whole lot more, like kill you from VRS above ETL which is a fugazi. It's a phony.

I've watched that video and the other VRS Mi-8 accident several times and I have two takeaways / observations: Number one: He has no forward momentum at all. None. That is to be expected when you descend straight down like he tried to. Number two: That pilot applied no corrective action. He pulled more collective. That tells me he didn't know what was wrong with his aircraft. He crashed from lack of training. He failed to identify the emergency proceedure and was therefore unable to apply corrective action. Which also tells me VRS accidents in the MI-8 are rare. Or there would be a strict training proceedures, proliferous amounts of literature, and way more accidents, none of which seems to exist. The Mi-8 is one of the most fielded helicopters in history, and you can find exactly two videos of VRS accidents and they are both pilot's going straight the hell down. Not moving, not above ETL. Those pilots crashed in vertical descent profiles, and they by all appearance, where caught completely off guard by VRS. That is not the same as the bird being overly dangerous. They were overly careless. Or they did not fully understand the flight profile they were operating in. And you still can't answer a simple question of mine. How does a helicopter encounter VRS above ETL. Have you watched the track files. Have you tested any of this yourself, or are you just trolling me at this point? Let's just start there and see if we can agree on one simple thing as fact. Can you get into VRS above ETL. It is a simple place to start. Yes or no?

To identify if there is a bug. Yes!, Of course, I think the model should be changed, if it is found to be incorrect. Who wouldn't? I don't understand why you can't look at the data? Or explain how a helicopter encounters VRS above ETL? You make an assertion everything is correct, but offer only reassurances and credentials without addressing the points made. My point is to find out if the flight model is accurate. You say yes. And you should know, but also can't answer my very simple questions, like how does a helicopter get into VRS above ETL. This should not be possible, do we agree on that?

I've heard a lot of people say essentially, "You're case is purely circumstantial!" And I will concede this point, with the caveat: it's a special kind of circumstantial. It's a Prima Facie case - Prima Facie - "sufficient to establish a fact or raise a presumption unless disproved or rebutted." In my track file, the aircraft enters VRS at 30 KIAS or about 55 kmph. This is above ETL and above ETL by the very definition of what ETL means, you physically cannot induce VRS, period. It's an aerodynamic impossibility. That is not circumstantial, that is prima facie. I don't need to prove the MI-8 VRS modelling is wrong, you need to prove to me that the MI-8 can in fact, encounter VRS at 55 kmph. On it's face, prima facie - everything we know about VRS says you must be below the effective transitional lift airspeed to encounter VRS. VRS is a phenomenon of re-ingesting the air you have induced a downward momentum. "Effective translational lift (commonly referred to as ETL) is a term used to describe the airspeed at which the entire rotor system realizes the benefit of the horizontal air flow. This happens when the helicopter's rotor disc moves completely out of its own downwash and into undisturbed air." "A vortex ring state is when the helicopter’s downwash recirculates into the induced flow and the helicopter descends while under power." The two are mutually exclusive. I don't have to prove that. It is correct on the face of it. My case is prima facie, a very special kind of circumstantial. I don't have to prove this point, it must be disproven, or the findings to be shown in error.

I've heard a lot of people say essentially, "You're case is purely circumstantial!" And I will concede this point, with the caveat: it's a special kind of circumstantial. It's a Prima Facie case - Prima Facie - "sufficient to establish a fact or raise a presumption unless disproved or rebutted." In my track file, the aircraft enters VRS at 30 KIAS or about 55 kmph. This is above ETL and above ETL by the very definition of what ETL means, you physically cannot induce VRS, period. It's an aerodynamic impossibility. That is not circumstantial, that is prima facie. I don't need to prove the MI-8 VRS modelling is wrong, you need to prove to me that the MI-8 can in fact, encounter VRS at 55 kmph. On it's face, prima facie - everything we know about VRS says you must be below the effective transitional lift airspeed to encounter VRS. VRS is a phenomenon of re-ingesting the air you have induced a downward momentum. "Effective translational lift (commonly referred to as ETL) is a term used to describe the airspeed at which the entire rotor system realizes the benefit of the horizontal air flow. This happens when the helicopter's rotor disc moves completely out of its own downwash and into undisturbed air." "A vortex ring state is when the helicopter’s downwash recirculates into the induced flow and the helicopter descends while under power." The two are mutually exclusive. I don't have to prove that. It is correct on the face of it. My case is prima facie, a very special kind of circumstantial. I don't have to prove this point, it must be disproven, or the findings to be shown in error.

@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.