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Vortex ring

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Vortex ring

Old 17th Oct 2017, 18:25
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Vortex ring

Hello guys! Just needed to know whether OGE is a prerequisite for entering vortex ring condition?
Cheers
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Old 17th Oct 2017, 20:55
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This should be good...
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Old 17th Oct 2017, 21:10
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Well you need a high rate of descent...
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Old 17th Oct 2017, 21:16
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Slow forward speed
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Old 17th Oct 2017, 22:01
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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).
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Old 17th Oct 2017, 22:18
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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.
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Old 18th Oct 2017, 09:40
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www.youtube.com/watch?v=HjeRSDsy-nEProbably the best video demonstration for Vortex Ring/ Settling with power.
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Old 18th Oct 2017, 16:05
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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.
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.
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Old 18th Oct 2017, 16:13
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... 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.
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Old 18th Oct 2017, 17:32
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Originally Posted by Rotorbee View Post
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.
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.
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Old 18th Oct 2017, 17:48
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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.
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Old 18th Oct 2017, 18:23
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Originally Posted by Rotorbee View Post
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.
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Old 18th Oct 2017, 19:37
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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.
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Old 19th Oct 2017, 07:40
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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.
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Old 19th Oct 2017, 09:01
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Old 19th Oct 2017, 10:41
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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?
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Old 19th Oct 2017, 13:13
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Blackhawk-CappyJax

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.
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Old 19th Oct 2017, 14:28
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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.
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Old 19th Oct 2017, 14:29
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Originally Posted by CappyJax
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).
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Old 19th Oct 2017, 14:35
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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.

Last edited by [email protected]; 19th Oct 2017 at 15:01.
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