DCS Huey and VRS

[LuckyFromArma]

I'm not sure if this is something I didn't notice that much before or if it's started due to the last update; when landing in the Huey I notice sometimes my Vertical airspeed getting above 500 fpm while my Airspeed is getting below 30 knts(as low as 15 knts) and I'm at more than 20% power.

 

At times I'm sure I should be getting into Settling With Power, but I don't.

 

I'm wondering if this is a bug that's came with the latest update, also wonder if there's a setting in a config file somewhere that I can tweak to make the physics more realistic? :unsure:

[cordite]

Are you a IRL rotary pilot?

[LuckyFromArma]

Are you a IRL rotary pilot?

 

I'm a lead farmer mother#*@#er! :lol:

[randomTOTEN]

I think your skills are improving. I haven't seen VRS in a very long time.

[LuckyFromArma]

I think your skills are improving. I haven't seen VRS in a very long time.

 

I'm sure both of those statements are true; however, I've put the aircraft into situations that definitely should have caused VRS, but it didn't happen.

 

I actually had to increase the decent rate to more than 800 fpm, sometimes over 1000 fpm didn't do the trick.

 

It's just not accurate all the time, sometimes it's almost on the numbers, but not quite, other times it's way out beyond plausible.

 

Sumpum's just not right about the model. :detective:

 

Surely there must a configuration setting somewhere that can be edited from Note Pad that will set the model to a realistic level. :idea:

Edited March 15, 2020 by LuckyFromArma

[cordite]

I'm a lead farmer mother#*@#er! :lol:

 

The point being, how do you know you should be getting into VRS that often? You don’t know. And your language tells me I don’t have to bother mincing words.

 

... I've put the aircraft into situations that definitely should have caused VRS, but it didn't happen.

Sounds like nonsense.
Edited March 15, 2020 by cordite

[Ramsay]

LuckyFromArma said:

... I've put the aircraft into situations that definitely should have caused VRS, but it didn't happen.

 

I actually had to increase the decent rate to more than 800 fpm, sometimes over 1000 fpm didn't do the trick.

 

It's just not accurate all the time, sometimes it's almost on the numbers, but not quite, other times it's way out beyond plausible..

 

Most RL pilots feel it's too easy to enter VRS in DCS.

 

This is a VRS risk assessment matrix, IRL there is no "fixed" figure that VRS will definitely occur at, only an increasing risk.

 

 

VRS Risk Formula c/o Gunnars Driver: https://forums.eagle.ru/showthread.php?p=4180185#post4180185

Edited January 6, 2021 by Ramsay
Update VRS risk to include AH-64D, etc.

[LuckyFromArma]

The point being, how do you know you should be getting into VRS that often? You don’t know. And your language tells me I don’t have to bother mincing words.

 

Sounds like nonsense.

 

I have a half dozen certificates from the FAA that say I know.

 

Here's what you need to get into VRS

 

Decent Rate greater than 300 feet per minute

Airspeed less than Effective Translational Lift ETL is around 16 to 24 knots or about 18 to 28 mph

Power/collective at 20% to 100%

 

If you have all of those conditions at the same time you will get into VRS in a helicopter.

[LuckyFromArma]

Most RL pilots feel it's too easy to enter VRS in DCS.

 

 

And what are you basing that statement on; posts that were made before the latest update?

 

Also what "RL pilots" are you referring to? Seems to me most RL pilots have probably never played DCS Huey. Were you trying to say "most RL pilots who have actually played DCS Huey"? It's not very clear, only that you're trying to appear that you know more than anyone else. Which you probably don't, and I couldn't really care less.:smartass:

 

Anyway, it seems like a simple fix; it's common knowledge among RL helicopter pilots that the conditions for VRS to occur are the sum of 300 fpm or greater decent rate + airspeed less than ETL + 20% to 100% power. All the developers have to do to make the model accurate is plug those into the model and it should work just fine; right? Unless they're working with some kind of plagiarized spaghetti code that no one over there understands. Or they're changing the sim from being an accurate sim to being something that's not really a sim to satisfy all those so called "RL pilots" who play DCS Huey.

 

That chart says it all; VRS in DCS isn't modeled for real life helicopters. When it comes to helicopters the conditions for VRS should look identical, it's physics, design doesn't change the laws of physics.

 

The really odd thing about it is, DCS has 2 modes of play, 1. Game Mode 2. Simulation Mode Why not make the Simulation Mode accurate??? and leave all the arcade physics in the Game Mode????

Edited March 17, 2020 by LuckyFromArma

[Ramsay]

... what "RL pilots" are you referring to?

Pilots that have flown the Huey IRL and taken the time to post feedback on these forums.

 

That chart says it all;

The chart is mine, not DCS's. It is based off Gunnars_Driver's RL risk assessment formula, and I used it compare the calculated VRS risk i.e. 0.5, with what is seen in DCS.

 

It uses DCS's helicopter mass and rotor diameters (where available) to calculate the downwash and a 0.5 descent value.

 

I thought it might be useful to the discussion and while you may disagree, it allowed you to explain your initial statement "At times I'm sure I should be getting into Settling With Power, but I don't."

 

VRS in DCS isn't modeled for real life helicopters. When it comes to helicopters the conditions for VRS should look identical, it's physics, design doesn't change the laws of physics.

 

Here's what you need to get into VRS

 

Decent Rate greater than 300 feet per minute

Airspeed less than Effective Translational Lift ETL is around 16 to 24 knots or about 18 to 28 mph

Power/collective at 20% to 100%

 

Ok, so you believe *all* DCS helicopters regardless of mass or rotor diameter should enter VRS with a descent rate greater than 300 ft/min (1.5 m/s), etc.

 

I'm not certain that's true but if you are claiming your 'facts' as a RL helicopter pilot, I'll respect your opinion.

 

The really odd thing about it is, DCS has 2 modes of play, 1. Game Mode 2. Simulation Mode Why not make the Simulation Mode accurate??? and leave all the arcade physics in the Game Mode????

How VRS is modelled in DCS has nothing to do with arcade mode, when things are adjusted it's due to feedback from RL Huey pilots and SME's, AFAIK the Huey's flight model hasn't changed since 1.5.x.

[cordite]

...I'm not certain that's true but if you are claiming your 'facts' as a RL helicopter pilot, I'll respect your opinion....

 

He’s claiming his facts as a “Lead Farmer”, and disrespectfully at that.

[LuckyFromArma]

Pilots that have flown the Huey IRL and taken the time to post feedback on these forums.

 

I'm think those "pilots" might be the same "pilots" the devs talked to.

 

Ok, so you believe *all* DCS helicopters regardless of mass or rotor diameter should enter VRS with a descent rate greater than 300 ft/min (1.5 m/s), etc.

 

I'm not certain that's true but if you are claiming your 'facts' as a RL helicopter pilot, I'll respect your opinion.

 

I've been working on various helicopter certifications for nearly 6 years now.

 

Greater rotor mass will only exacerbate VRS.

 

When in VRS you're recirculating your own down wash.

 

VRS occurs when your wingtip or rotor tip vortexes enlarge and spread across a greater portion of the rotor disk reducing lift, because the air is being push down at a greater velocity making it difficult for the rotors to produce lift.

 

Applying more power during VRS, in an effort to get more lift, will only cause you to sink faster due to increased recirculation of your down wash.

 

How VRS is modelled in DCS has nothing to do with arcade mode, when things are adjusted it's due to feedback from RL Huey pilots and SME's, AFAIK the Huey's flight model hasn't changed since 1.5.x.

 

Simulation Mode behaves more like Game Mode/Arcade Mode. I see people on here saying things like "To get into VRS in DCS Huey you have to have a decent rate of at least 900 fpm" That's not realistic. 300 fpm is enough if you're heavy or the density altitude is high. 500 fpm is a no no during a Normal Landing.

 

It's the part right at the bottom of the landing that is crucial, because that's where your Forward Airspeed and your Decent Rate and your Power Setting are all going to be closest to the magic numbers for VRS.

 

If you keep your Forward Airspeed around 30 knots and your Decent Rate less than 300 fpm you won't get into VRS. Start falling below 20 knots Forward Airspeed with a Decent Rate of 600 fpm and you should get into VRS.

 

If I'm in Simulation Mode I expect it to happen under those conditions, when it doesn't I start experimenting to see where it does, and I'm disappointed to find that I have to hover OGE and descend at 1000 fpm to get into VRS, even then sometimes I'm able to catch it by increasing collective at the bottom(around 20 feet from the ground). The Huey has a 48' rotor disk, a little bigger, but for the sake of simplicity, so at 24' it's in ground effect, but that's not going to halt a full blown VRS induced crash from 150' feet AGL. That requires cartoon physics.

[Ramsay]

Greater rotor mass will only exacerbate VRS.

It's not rotor mass, rather the gross weight of the helicopter is used to calculate the thrust/downwash.

 

If you keep your Forward Airspeed around 30 knots and your Decent Rate less than 300 fpm you won't get into VRS. Start falling below 20 knots Forward Airspeed with a Decent Rate of 600 fpm and you should get into VRS.

 

That may be true for older/lighter helicopters with lighter rotor loading but there are a number of anecdotes from pilots and instructors on http://www.pprune.org/rotorheads that cite descent rates of ~900 fpm and similar before entering a FULL VRS with the loss of thousands of feet of altitude i.e. after a student raises collective instead of lowering to breakout of VRS.

 

Taking Gunnars_Driver's risk formula and say applying it to an R22, agrees with the VRS chart for that helicopter (note I don't recall the chart's original source).

 

Vih = Theoreticall downwash = Square root of ( T / ( 2 x p x A) )

Aircraft       = R22						
Weight (w)     = 1370lbs       = 623 kg
Thrust (T=wg)  = 6109 N
Rotor Diameter = 25.2 ft       = 7.7 m
Rotor Area A   = 46.332 m^2
Downwash Vih   = 7.336 m/s     = 1445 ft/min	
0.5 * Vih      = 3.7 m/s       = 723 ft/min

 

The same answer (Vd/vi = 0.5) graphically :

 

 

So I hope you'll understand my dissenting opinion.

 

Note: On PPRuNe the opinion seemed to be that 0.65 * Vih equated to a fully developed VRS but, as a discussion forum, there were a number of differing opinions.

Edited March 18, 2020 by Ramsay

[LuckyFromArma]

It's not rotor mass, rather the gross weight of the helicopter is used to calculate the thrust/downwash.

 

That may be true for older/lighter helicopters with lighter rotor loading but there are a number of anecdotes from pilots and instructors on http://www.pprune.org/rotorheads that cite descent rates of ~900 fpm and similar before entering a FULL VRS with the loss of thousands of feet of altitude i.e. after a student raises collective instead of lowering to breakout of VRS.

 

The heavier you are and/or the higher the density altitude, or the higher you actually are the lower the performance of the aircraft. That's true for all aircraft regardless of design.

 

There are variables that in the right situation will make it more "difficult" for lack of a better word, to get into VRS, say an up draft on a warm day or low density altitude when there's more air to fly in.

 

If I'm correct the conditions in DCS Huey Free Flight are average conditions so the chance of getting into VRS should be pretty good if you don't mind your airspeed/descent rate.

 

Before I updated to the newer version VRS was modeled much closer to what I expect it to be, but now it's almost impossible to get into VRS without deliberately going out of my way to get there. I mean it actually takes a lot of effort. Not exactly accurate modeling for the number one killer of helicopter pilots. Ya know?:joystick: Well, maybe it's number 2, because flying VFR into IMC(a.k.a. weather) is number 1.

 

Maybe DCS will add the Robinson R22 to it's line up and we can see how easily the helicopter that CFI's refer to as the meteor gets into VRS.

Edited March 18, 2020 by LuckyFromArma

[pbishop]

And what are you basing that statement on; posts that were made before the latest update?

 

Also what "RL pilots" are you referring to? Seems to me most RL pilots have probably never played DCS Huey. Were you trying to say "most RL pilots who have actually played DCS Huey"? It's not very clear, only that you're trying to appear that you know more than anyone else. Which you probably don't, and I couldn't really care less.:smartass:

 

Anyway, it seems like a simple fix; it's common knowledge among RL helicopter pilots that the conditions for VRS to occur are the sum of 300 fpm or greater decent rate + airspeed less than ETL + 20% to 100% power. All the developers have to do to make the model accurate is plug those into the model and it should work just fine; right? Unless they're working with some kind of plagiarized spaghetti code that no one over there understands. Or they're changing the sim from being an accurate sim to being something that's not really a sim to satisfy all those so called "RL pilots" who play DCS Huey.

 

That chart says it all; VRS in DCS isn't modeled for real life helicopters. When it comes to helicopters the conditions for VRS should look identical, it's physics, design doesn't change the laws of physics.

 

The really odd thing about it is, DCS has 2 modes of play, 1. Game Mode 2. Simulation Mode Why not make the Simulation Mode accurate??? and leave all the arcade physics in the Game Mode????

 

So sensitivity training taught me I can't tell someone they are stupid, so I ask people now instead. At what point when you were paraphrasing page 11-10 of the FAA's Helicopter Flying Handbook, in the most out of context way, did you think this was an accurate way of modeling VRS?

 

Yes, even RL helicopter pilots and flight test engineers get sensitivity training. :poster_oops:

 

I needed to edit this, something was missing...... Although NASA has been known for not using common knowledge, here is how they apparently don't model it correctly for anyone interested:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060024029.pdf

Edited March 19, 2020 by pbishop

[LuckyFromArma]

Look at this.....

 

 

 

0 Airspeed

1200 FPM Descent Rate

IGE Hover Power

 

No VRS

Edited March 19, 2020 by LuckyFromArma

[LuckyFromArma]

So sensitivity training taught me I can't tell someone they are stupid, so I ask people now instead. At what point when you were paraphrasing page 11-10 of the FAA's Helicopter Flying Handbook, in the most out of context way, did you think this was an accurate way of modeling VRS?

 

Yes, even RL helicopter pilots and flight test engineers get sensitivity training. :poster_oops:

 

I needed to edit this, something was missing...... Although NASA has been known for not using common knowledge, here is how they apparently don't model it correctly for anyone interested:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060024029.pdf

 

You definitely need Sensitivity Training.

[msalama]

And you may need a refresher course on VRS, among other things. Just sayin'.

[Ramsay]

Look at this.....

 

 

0 Airspeed

1200 FPM Descent Rate

IGE Hover Power

 

No VRS

 

Interesting.

 

The R22 VRS chart does show reduced VRS effects for steep (i.e. 90°) descent angles but I'd have expected some turbulence, etc., perhaps they're not modelled in DCS.

Edited March 19, 2020 by Ramsay
UH-1H Free Flight mission has a light surface wind.

[LuckyFromArma]

Interesting.

 

The R22 VRS chart does show reduced VRS effects for steep (i.e. 90°) descent angles but I'd have expected some turbulence, etc., perhaps they're not modelled in DCS.

 

The fact that the descent rate went right to 1200 fpm and just stayed there. It's like they imposed some kind of VRS speed limit where you reach a certain descent rate and it doesn't accelerate like it would in real life, then ground effect comes in right at the very bottom.:lol:

[imaner76]

Alright! Don't get yourselves in a spin over it, this is descending quickly.

 

 

 

 

*gets coat. TAXI :music_whistling:

[randomTOTEN]

Look at this.....

 

 

 

0 Airspeed

1200 FPM Descent Rate

IGE Hover Power

 

No VRS

Works on my machine

[LuckyFromArma]

Works on my machine

 

What do you mean "Works on my machine"?

[LuckyFromArma]

Alright! Don't get yourselves in a spin over it, this is descending quickly.

 

 

 

 

*gets coat. TAXI :music_whistling:

 

No it's descending at 1200 fpm and not one bit faster no matter how far it falls. :pilotfly:

 

I could descend from 26000 AGL at 1200 fpm and end up in an IGE hover and never touch the collective.

[Gunnars Driver]

I have a half dozen certificates from the FAA that say I know.

 

Here's what you need to get into VRS

 

Decent Rate greater than 300 feet per minute

Airspeed less than Effective Translational Lift ETL is around 16 to 24 knots or about 18 to 28 mph

Power/collective at 20% to 100%

 

If you have all of those conditions at the same time you will get into VRS in a helicopter.

 

Nope, you wont.

 

IRL most helicopters airspeed indicator reallty doesnt show reliable airspeed below 20-30 knots( depending on type). In m o s t cases you need to se zero on the ASI to be able to enter VRS.

The air speed can not really be higher than the indiudeced downwash, otherwise you fly out of the VRS. In real life, max 20knots TAS.

 

The 300f fpm minute is the value you learn helo students, mostly flying light helos with small downwash-numbers, but 300 is the safe level with some margin even for the helos with the smallest downwash.

 

Those numbers Ramsay referred to is true. It is very easy to prove. This is because there have been a lot of research and most(actually I’d say all) of the research results agree. There is a lot of info on this. I you are sure its wrong, you might want to call NASA and tell them their data is wrong...

 

Basically, VRS is a question of descending into your own downwash. If you fly a light helo with lower speed of downwash, you’ll enter it with a lower descent rate.

If you fly a heavier helo with higher speed of downwash, like the NH90 in my avatar; Im the pilot flying in that picture, you have to descend faster to keep up with the downwash speed.

 

For the same helo, being lighter causes lower downwash making the helo enter VRS at a lower descent rate. Higher weight gives faster downwash and thereby ois safer when it comes to VRS only.

Hot and high, in thin air gives faster downwash, so you have to descend faster to reach the downwash and VRS.

 

And for virtually any helo 20% TQ isnt enough to cause VRS. 20% TQ is around what it takes to just turn the rotor flat pitch at 100% NR. So youy need more power than that. Of course it depends on the type, but id say as a general note, 40-50% or more.

 

I actually did some VRS entry the other week. Was a proficency check for my civil ATPL papers.

I did actually have 0 feet per minute but I did fly downwind and raised the nose to reduce speed and keeping power high when speed reduce to zero to enter VRS. For these the goal was to show that I did the correct action early when entering VRS, lowering nose and flying out of it before it develops to a more dangerous situation.

 

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060024029.pdf

 

https://pdfs.semanticscholar.org/bad8/f350815c2b754cd3472bc254238484b06bd6.pdf