Vortex ring

[Salmanhj]

Hello guys! Just needed to know whether OGE is a prerequisite for entering vortex ring condition?
Cheers

[feathering tickles]

This should be good...

[chopjock]

Well you need a high rate of descent...

[500e]

Slow forward speed

[n5296s]

I think the answer has to be an unequivocal "yes". If you're not OGE then by definition you must be IGE. And if you enter vortex ring while you're IGE, for sure it won't last long. With any luck the worst damage will be a couple of bent skids, though I guess a rollover is more likely. But anyway it won't have lasted long.

Unless of course you use the Vuichard technique, which guarantees a quick and safe recovery. (Oops, sorry, it just slipped out. Just kidding, guys).:E

[CappyJax]

Are you asking that if proximity to the ground will eliminate the VRS?

You can't enter VRS when IGE because you won't be able to obtain the ROD needed to develop the large vortices. If you are in VRS and you near the ground, the ground will have the same effect as if you are in a hover which will reduce the size of the vortices. So, the ground may slightly reduce the effect of VRS for a moment right before you impact the ground.

[Surendra_Simrik]

www.youtube.com/watch?v=HjeRSDsy-nE
Probably the best video demonstration for Vortex Ring/ Settling with power.

[Rotorbee]

Before anybody has the chance let me do it ...
Dear Surendra_Simrik
This video and the ones before and the website and ... and ... and Mr Vuichard have been subject of a rather interesting discussion before.
Please go HERE (http://www.pprune.org/rotorheads/557861-vuichard-technique-settling-power.html?highlight=vuichard).
Please read carefully what some of the more experienced members have to say.
Just a hint, what to expect. Settling with power and Vortex Ring State are two completely different things and should not be used in the same sentence. Better not even in the same thread.
Have fun.

[Rotorbee]

... oh and before I forget. Settling With Power can occur in IGE. That' that sudden inexplicable power loss pilots always mention after SWP occurs.
VRS in IGE? Very hard to do find out if it works.

[CappyJax]

Before anybody has the chance let me do it ...
Dear Surendra_Simrik
This video and the ones before and the website and ... and ... and Mr Vuichard have been subject of a rather interesting discussion before.
Please go HERE (http://www.pprune.org/rotorheads/557861-vuichard-technique-settling-power.html?highlight=vuichard).
Please read carefully what some of the more experienced members have to say.
Just a hint, what to expect. Settling with power and Vortex Ring State are two completely different things and should not be used in the same sentence. Better not even in the same thread.
Have fun.

I just read some of that thread. I am shocked at how many pilots have gotten into some very bad VRS. I can think of only one time I thought I might have been getting into it and I just increased my airspeed a bit. I think we might need more focus on avoidance if that many pilots are regularly getting into VRS.

And yes, VRS and settling with power are not the same thing despite the FAA trying very hard to make them the same. However, they can look similar to those who don't understand the aerodynamics involved. For example, OGE at a high gross weight with insufficient power to hover will results in a descent. You are settling into your own wake, so the helicopter will be effected by the turbulence. The ROD might only be a couple hundred feet per minute, but you are only settling into your downwash, you have not yet caught up to up. If the rate of descent increases to the point of catching up to your own downwash, VRS starts to develop. So, settling with power can lead to VRS, but the aerodynamics involved are very different. I think why the FAA makes them out to be the same in that the recovery is generally the same which is to increase speed beyond ETL. However, if you lower collective when settling with power, you may put yourself into VRS trying to recover and will require more down collective to get out of VRS. Whereas, if you had just lowered the nose and increased speed, you would easily fly out of settling with power.

[Rotorbee]

Most of our colleagues got into VRS in training missions. Despite what Vuichard claims, there are not thousands of lifes lost due to VRS.
Most Settling With Power accidents happen close to the ground to the "complete surprise" of the pilot. I think that the clues that you do not have the power to hover OGE are pretty clear (collective under the arm and still going forward) and most pilots get not into VRS because they do not have the power to hover but just because we sometime are just dump, fat and happy. Tailwind is another often used method. (See REGA accident)
What am I doing? I stop now, we had all this already.

[CappyJax]

Most of our colleagues got into VRS in training missions. Despite what Vuichard claims, there are not thousands of lifes lost due to VRS.
Most Settling With Power accidents happen close to the ground to the "complete surprise" of the pilot. I think that the clues that you do not have the power to hover OGE are pretty clear (collective under the arm and still going forward) and most pilots get not into VRS because they do not have the power to hover but just because we sometime are just dump, fat and happy. Tailwind is another often used method. (See REGA accident)
What am I doing? I stop now, we had all this already.

Does he really claim thousands of lives lost due to VRS? I think the most number of lives lost from VRS was in the V22. The military might have a lot more of them than the civilian world. For light helicopters, the box is pretty small. But for heavy helicopters with high disk loading, the box gets really really big. A Blackhawk at gross weight is in the heavy turbulence area of VRS at 26 knots and 1700 FPM, and may still be in the light turbulence regions at speeds as high as 80 knots. That is a really big area to avoid.

[Rotorbee]

Yupp, he does. The man is on a mission. He said that his Vuichard-Technique will save so many lives, that he will be in the Smithsonian. Alongside Hoover and Lindberg. Well, he does not suffer from inferiority complex. But he is Swiss and since the Swiss are the only ones that know anything about helicopter flying, he must be right.
Lately a Swiss airport director (Sion) bragged about the great Swiss pilots (she holds a PPL-SEL, longest flight, Corsica) compared to pilots in Arizona where the highest elevation are the pebbles on the runway.
Well you get the point. The accident rate of the Swiss is nothing to write home about but still, must be the best, because of the mountains.
Back to the Blackhawk. Would you be so kind and give us the chart for VRS? I would be very interested.

[[email protected]]

A Blackhawk at gross weight is in the heavy turbulence area of VRS at 26 knots and 1700 FPM, and may still be in the light turbulence regions at speeds as high as 80 knots. That is a really big area to avoid. No.
The higher the disc loading, the higher the speed of the downwash and therefore the higher your RoD needs to be in order to catch up with your downwash.

Light helicopters with low disc loadings are much more susceptible to VRS.

They are also more susceptible to SWP since they run out of power quickly.

Do we really need to go round this buoy again and again?

If you are going to hover OGE, make sure you have enough performance to do so with pre-flight planning and a power available check. Ideally have some performance to spare to allow for turbulence, mishandling etc.

Don't make downwind approaches, especially to OGE, without thinking carefully about it and ensuring you have even more power in hand.

If you want to come to an OGE hover make it a level approach in the latter stages as it uses less power (you don't have to kill RoD) and it is easy to spot if you are getting close to your power limit.

Give yourself a escape route of clear air you can fly into.

If you are below ETL (10 - 15 Kts) and you have more than 3 or 400 ft/min RoD with power applied, you are right in the bracket for IVRS which could quickly become VRS - just avoid low speed descents.

[Thomas coupling]

Zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz zzzzzzzzzzzzzzzzzz:ugh:

[chopjock]

crab,
No.
The higher the disc loading, the higher the speed of the downwash

I am a bit confused here, The higher the disc loading, the more pitch on the blades, right? so more air being pushed downwards, but same RRPM, would that air be faster or just more of it?

[JohnDixson]

Re Post 13:

The UH-60 ( or any of our other machines ) is not in VRS at 26kts/-1700FPM.

The n/rev roughness that may be felt at speeds/rates of descent in that area is the result of one advancing blade intercepting the tip vortex from the preceding blade.

In fact, if one looks at the standard flight test card at SA for a flight loads survey test flight, one will see a maneuver called a Rough Approach and this is how it is flown. Now, the numbers, I.e., airspeed and ROD can vary depending on the GW and CG ( remember, it's the intersection of the vortex that trips the n/rev vibration ) but it is findable on everything from the S-58 to the S-92. Note:This flight condition does not result in any of the sharp peaked pitch and roll attitude excursions symptomatic of VRS.

[ShyTorque]

John, This is probably similar to what we found on the Puma when required to enter a very much HOGE hover in as 'quiet' a manner as possible. Flying level or descending was very noisy. We found a gently climbing quickstop was the best way to achieve it.

[Lonewolf_50]

A Blackhawk at gross weight is in the heavy turbulence area of VRS at 26 knots and 1700 FPM, and may still be in the light turbulence regions at speeds as high as 80 knots. Cappy: are you referring to airspeeds as high as 80 kts being in the range of VRS?
At 80 knots in a Black Hawk you are well through translational lift, and not too far from L/D max (max fuel conserve airspeed, max power margin, of course DA/GW dependent) and pretty close to optimal autorotation airspeed (DA and GW dependent) with if memory serves a few knots to spare.
Was 80 knots a typo there? Your post confused me for multiple reasons, but that in particular makes no sense to me. What point were you trying to get across? In flight vibration levels, or something else?


(Memory banks are a bit foggy; while we flew most of our maintenance autos at ~80 KIAS, I seem to recall learning that the sweet spot was somewhere between 70 and 75 kts. I am sure Mr Dixson can fine tune that with his experiences in developing that helicopter).

[[email protected]]

I am a bit confused here, The higher the disc loading, the more pitch on the blades, right? so more air being pushed downwards, but same RRPM, would that air be faster or just more of it? Disc loading is a function of how big the disc is compared to how much weight it is supporting.

Two helicopters with the same size rotor disc but with different AUM will have different disc loadings - the higher the AUM, the higher the disc loading for the same size rotor. Would that mean higher pitch angles? Probably but only if RRPM and the size/shape/number of blades is constant. There is a ratio called rotor solidity ratio which is the swept area of the disc divided by how much of that area is occupied by the blades.

As engines have become more powerful over the years, it has allowed designers to reduce the size of the rotor disc because more power means you can make the disc 'work' harder.

You are just pushing the same amount (volume) of air downwards (for the same aircraft mass) but with a smaller rotor (smaller cross-sectional area) so the downwash speed has to be increased by accelerating the air more.

I'm no physics guru but I think you are doing the same amount of work (same volume of air) in less time and power is a function of work/time - hence the need for more powerful engines to allow a smaller rotor disc.

[JohnDixson]

ST: No reason the Puma and AH 332/225 etc would not exhibit similar tendencies, with the degree of n/rev excitation as sensed in the cockpit dependent upon the vibration attenuation system/design attributes. And as one would expect, it is much easier to find this condition and stay on point for data purposes if the wind is calm or nearly so.

LW: The maintenance test flight manuals for the S-70 models are similar and the auto Nr charts ( which are simply a cross check on collective rigging being proper on the low end ) were developed based on performing the auto at 80 KIAS and stable.

[CappyJax]

No.
The higher the disc loading, the higher the speed of the downwash and therefore the higher your RoD needs to be in order to catch up with your downwash.

Light helicopters with low disc loadings are much more susceptible to VRS.

They are also more susceptible to SWP since they run out of power quickly.

Do we really need to go round this buoy again and again?

If you are going to hover OGE, make sure you have enough performance to do so with pre-flight planning and a power available check. Ideally have some performance to spare to allow for turbulence, mishandling etc.

Don't make downwind approaches, especially to OGE, without thinking carefully about it and ensuring you have even more power in hand.

If you want to come to an OGE hover make it a level approach in the latter stages as it uses less power (you don't have to kill RoD) and it is easy to spot if you are getting close to your power limit.

Give yourself a escape route of clear air you can fly into.

If you are below ETL (10 - 15 Kts) and you have more than 3 or 400 ft/min RoD with power applied, you are right in the bracket for IVRS which could quickly become VRS - just avoid low speed descents.


Much higher than 1700 FPM???? There are actually graphs and formulas for VRS, yeah know?

[CappyJax]

Cappy: are you referring to airspeeds as high as 80 kts being in the range of VRS?
At 80 knots in a Black Hawk you are well through translational lift, and not too far from L/D max (max fuel conserve airspeed, max power margin, of course DA/GW dependent) and pretty close to optimal autorotation airspeed (DA and GW dependent) with if memory serves a few knots to spare.
Was 80 knots a typo there? Your post confused me for multiple reasons, but that in particular makes no sense to me. What point were you trying to get across? In flight vibration levels, or something else?


(Memory banks are a bit foggy; while we flew most of our maintenance autos at ~80 KIAS, I seem to recall learning that the sweet spot was somewhere between 70 and 75 kts. I am sure Mr Dixson can fine tune that with his experiences in developing that helicopter).

I was looking at the chart wrong. I haven't looked at it in over a decade, so I followed the airspeed column up the approach angle lines when i should have went vertical. So, the range is up to 26 knots, and vertical descents from 1786FPM to 3383FPM will put you in VRS in a black hawk. That is a pretty large envelope compared to an R22 which is 14 knots and 927 fpm to 1756 fpm at gross weight. Or even a lightly loaded black hawk at 12,000 pounds which would be 20 knots, 1319 FPM to 2500 FPM

The higher the gross weight (higher disk loading), and the higher the altitude creates a faster downwash and a larger envelope which to avoid. Albeit, at a higher ROD which may make it easier to avoid. The lower the gross weight (lower disk loading), and the lower the altitude creates a slower downwash and a smaller envelope to avoid.


Main Rotor Radius 26.9
Disk Area 2273.28786006411
Weight 22000
Disk Loading 9.67761293520459
Air Desnity 0.002377

Vi 2707.10926827765
Vi min .66 1786.69211706325
Vi max 3383.88658534706
Vi Peak 14.6835315340503
Vi 1 26.6973300619097
Vi 2 53.3946601238194
Vi 3 80.0919901857291

[Lonewolf_50]

I was looking at the chart wrong. OK, that can happen to any of us. :cool:

John Dixson. Understood on the auto check airspeed, but I seem to recall a discussion (and maybe G12 was in the room, memory fails) about getting the RoD to drop a bit by flying the profile a few knots below 80 if you had a real auto ... but honestly, this could just be bad memory. 80 IAS was more or less Scripture unless one wanted that long flare 'max range' auto that one flew at 100 kts IAS.

[[email protected]]

The higher the gross weight (higher disk loading), and the higher the altitude creates a faster downwash and a larger envelope which to avoid. Albeit, at a higher ROD which may make it easier to avoid. The lower the gross weight (lower disk loading), and the lower the altitude creates a slower downwash and a smaller envelope to avoid. it's not a smaller envelope to avoid - it means you can get into VRS easier (ie with lower RoD) in an aircraft with a lower disc loading. You have to have a higher RoD to get into VRS in a helo with a high disc loading.

Hence, smaller and lighter helicopters are more vulnerable to VRS since you can encounter it at lower RoD than in a big, heavy powerful military helo.

Much higher than 1700 FPM???? There are actually graphs and formulas for VRS, yeah know? no. really??? The graph you are referring to was posted on here many years ago by Nick Lappos - it shows that you need to have a RoD around half to 0.6 of your downwash speed to encounter IVRS and around 0.7 to be in fully developed VRS,

[JohnDixson]

LW, Re Post #25: ( a bit off subject-sorry )

Chris ( G-12 ) was correct re 80 being a bit higher than min auto ROD for the S-70, but that isn't the only factor going into the recommended, and therefore the auto Nr chart. Selecting the speed for the flare is critical: too slow and all you do is change the pitch attitude without killing off enough of the vertical speed; too high and with what the average pilot would use for a flare in terms of pitch rate, and you get a balloon, which leaves you with plenty of Nr, but too high,and you'll lose that excess Nr coming out of the flare and well before the collective has to be applied for the landing. For the S-70 models ( UH and SH ) 80 was the best compromise. Similar considerations led to the values selected for the 76 and 92 ( and prior to that, for the 64 and 65 models ).

We had a textbook case of what happens when the speed is too slow one day in Stratford. For reasons I cannot recall, a full auto was thrown onto the end of a very different test card. It was a quite windy day, with a cold front having passed thru previously. Gust spread was significant. The non flying pilot was perhaps the test pilot most experience with autos at SA ( ouch ). But not to worry, the other pilot wasn't exactly an amateur either, right? (Not me )

The approach had to be to the west over the river next to the SA heliport and there was a slight ridge opposite the field. Later data from the tower showed that at the point of flare, the wind dropped 15 kts, so that the flare was performed at 65, not 80. You may have seen the film-it has been on the Internet. Aircraft flared, and all those associated data traces look exactly like the successful full autos done previously, but the tail wheel hit the ground at around 42 fps. Broke the wheel and crunched the aft 2 inches of the stabilator. Very embarrassing. In the video, it is clear that the flare did little except change the pitch attitude of the machine, and the data said the same.

[CappyJax]

it's not a smaller envelope to avoid - it means you can get into VRS easier (ie with lower RoD) in an aircraft with a lower disc loading. You have to have a higher RoD to get into VRS in a helo with a high disc loading.

Hence, smaller and lighter helicopters are more vulnerable to VRS since you can encounter it at lower RoD than in a big, heavy powerful military helo.

no. really??? The graph you are referring to was posted on here many years ago by Nick Lappos - it shows that you need to have a RoD around half to 0.6 of your downwash speed to encounter IVRS and around 0.7 to be in fully developed VRS,

Why are you repeating what I say and then contradicting what I say? And please tell me how the envelope is not larger when I actually presented the numbers from the actual forumla comparing the same helicopter at minmum weight and gross weight. Seriously dude, you have issues.

[[email protected]]

Because you talked about it being a larger or smaller 'envelope' for avoidance of VRS - implying that the larger your 'envelope' the easier it is to get into VRS.

That is completely wrong and I would hate less experienced pilots to think that if you have a 'small envelope' in a lighter helo that you are safer and further away from VRS when it is exactly the opposite.

I think you should read what you have written and look back across the plethora of threads on pprune about VRS.

Don't talk about 'envelopes', it is counter-intuitive and utterly useless in the real world.

I have put some practical suggestions as to how to avoid VRS in my previous posts based on real-world situations and experience.

The only issues I have are with pilots not understanding how VRS can be encountered.

[CappyJax]

Because you talked about it being a larger or smaller 'envelope' for avoidance of VRS - implying that the larger your 'envelope' the easier it is to get into VRS.

That is completely wrong and I would hate less experienced pilots to think that if you have a 'small envelope' in a lighter helo that you are safer and further away from VRS when it is exactly the opposite.

I think you should read what you have written and look back across the plethora of threads on pprune about VRS.

Don't talk about 'envelopes', it is counter-intuitive and utterly useless in the real world.

I have put some practical suggestions as to how to avoid VRS in my previous posts based on real-world situations and experience.

The only issues I have are with pilots not understanding how VRS can be encountered.


I said "The higher the gross weight (higher disk loading), and the higher the altitude creates a faster downwash and a larger envelope which to avoid. Albeit, at a higher ROD which may make it easier to avoid. The lower the gross weight (lower disk loading), and the lower the altitude creates a slower downwash and a smaller envelope to avoid. "

I didn't imply ANYTHING! I specifically said that it may be easier to avoid. And YES, the envelope is LARGER. I provided actual evidence of it using the prescribed FORMULA! I am not spouting a belief like you. Seriously dude, you remind me of AvBug! At least try reading and understand what someone is saying before you attack them for saying the EXACT SAME THING AS YOU!

[[email protected]]

You actually said the UH60 could be in the VRS envelope at 80 kts (light turbulence) and in heavy turbulence at 26 kts and 1700'/min and then, once corrected you produced a list of numbers Main Rotor Radius 26.9
Disk Area 2273.28786006411
Weight 22000
Disk Loading 9.67761293520459
Air Desnity 0.002377

Vi 2707.10926827765
Vi min .66 1786.69211706325
Vi max 3383.88658534706
Vi Peak 14.6835315340503
Vi 1 26.6973300619097
Vi 2 53.3946601238194
Vi 3 80.0919901857291 with no units or explanation and then started talking about envelopes when you actually mean a larger area on the graph.
You repeated that a smaller envelope is 'easier to avoid' as if that makes it less likely to get into VRS with a low disc loading helicopter which I now have to repeat is not the case.

Ever taught IVRS, VRS and recovery? Ever had either?

[CappyJax]

You actually said the UH60 could be in the VRS envelope at 80 kts (light turbulence) and in heavy turbulence at 26 kts and 1700'/min and then, once corrected you produced a list of numbers with no units or explanation and then started talking about envelopes when you actually mean a larger area on the graph.
You repeated that a smaller envelope is 'easier to avoid' as if that makes it less likely to get into VRS with a low disc loading helicopter which I now have to repeat is not the case.

Ever taught IVRS, VRS and recovery? Ever had either?


DO YOU HAVE READING COMPREHENSION PROBLEMS??? Here, I will post what I said a third time, and maybe you will read it.

I said "The higher the gross weight (higher disk loading), and the higher the altitude creates a faster downwash and a larger envelope which to avoid. Albeit, at a higher ROD which may make it easier to avoid. The lower the gross weight (lower disk loading), and the lower the altitude creates a slower downwash and a smaller envelope to avoid. "

If you know everything there is to know about VRS, then tell me what you would teach to someone so that they could always avoid it.

[Hughes500]

So Cappy

What happens after 1756 fpm in an R22 does it come out of VRS ?

[chopjock]

Faster downwash, slower downwash?
If you have two helicopters of the same type, side by side at the same DA, same RRPM, one at min take off mass and the other at max, the speed of the downwash would be the same, just the heavier one has to push more air. Surely the speed of the downwash is dependent on the RRPM and the amount of the downwash is dependent on the disc loading?

[[email protected]]

Chopjock - yes the heavier one has to push more air, so how does it do that with the same RRPM and the same blades? It has to accelerate the air using more pitch and more power to produce a higher speed of downwash.

Cappy If you know everything there is to know about VRS, then tell me what you would teach to someone so that they could always avoid it.
I did exactly that in an earlier post.#15

You keep repeating your post about 'envelopes' and making it easier or more difficult to avoid them - what is the actual point you are trying to make?

Can you not understand that when you say it is easier to 'avoid the smaller envelope' of a light helicopter, that it looks like you are saying it is easier to avoid VRS in a light helicopter????

As we have both established, the lower downwash speed of a lightly loaded helicopter means you can reach the required parameters for VRS much more easily (that makes it more dangerous) than in a helicopter with a heavily loaded disc.

This is all about terminology - the facts are that a lightly loaded helicopter is far more likely to encounter VRS in a steep and slow approach than a heavily loaded one because it only has to reach a much lower RoD to start ingesting its own downwash.

Is that clear and comprehensive enough to make you understand?

[army_av8r]

Vortex ring "state" is a state that occurs when the rate of decent, and upflow from descending meet each other at a ratio. The "envelope" is very dynamic because it is a factor of rotor thrust output along with rate of descent. Typically a rate of descent that is
Between 25% and 42% of your induced flow velocity is sufficient to see indications of the incipient phase, if that ratio is allow to increase to around 75%, a fully developed vortex ring state will be encountered. The "envelope" will be larger with heavy machines that are capable of producing large amounts of rotor thrust. Butt those envelopes start a much higher rate of descent too. Small single engine piston aircraft will have narrower envelopes but the region begins at a much slower rate of descent. Therefore those operators are more likely to see VRS on a day to day basis. Since the ROD falls much closer to what is considered a "normal" rate.

[[email protected]]

Which is pretty much what I have posted already but without the use of the word 'envelope' since it can be misleading.

All we are talking about is rates of descent - something every pilot can easily relate to - big, heavily loaded aircraft won't encounter VRS until they have RoDs well in excess of 1000'/min whereas smaller, lighter helos can encounter VRS at RoDs well under 1000'/min.

Expanding the speed part of the 'envelope' is pretty pointless since you are unlikely to encounter VRS above ETL which doesn't really vary much with helicopter size.

[army_av8r]

I completely agree, the "envelope" should really only include vertical speed. But it must also include power applied. Since both are required to get established in VRS. once someone has actually put an aircraft into VRS, this discussion becomes easy. This is a flight regime that just doesn't translate as well into words. Once you truly
Are trained to fly into it, it'll all make sense.

[[email protected]]

army_av8r - :ok:

[albatross]

Geeze... how many times do we have to "Dance around the Maypole" about this subject?

[BOBAKAT]

Vertical descent above 300ft/mn down wind or low speed.... that's suffisant to gone VRS.
but not only...My first VRS was in approach with low speed and 150 ft/mn...But i was number 2 or 3 and 3 more chopper close behind me... The downwash of the other helicopters combined with my own put me in VRS
I was young pilot and have a old one Captain in the other seat : He push the stick in front and pitch down....I finish the approach number one