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Condition for Vortex Ring

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Condition for Vortex Ring

Old 28th Nov 2017, 07:13
  #101 (permalink)  
 
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Lonewolf - the trouble with Mr Prouty's suggestion is that the term 'Thrust Instability' is at least as ambiguous as SWP as a description for VRS.

And, since getting the genie back in the bottle won't happen, we will just have to keep having debates like this one to at least highlight to the less experienced that there is a real difference between the two conditions.
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Old 28th Nov 2017, 09:06
  #102 (permalink)  
 
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And to think our Royal's have to go through this langauge barrier - now.
I bet the words "thrust" and fanny come into it somewhere, no doubt.
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Old 28th Nov 2017, 09:12
  #103 (permalink)  
 
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USA / Great Britain, a whole community only separated by a language....
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Old 28th Nov 2017, 12:54
  #104 (permalink)  
 
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To our friends in the UK, from the colonies:

Please go to Amazon UK and pick up a copy of:

“ Made in America, An Informal History of American English” by Bill Bryson,2016. L8.99.

All will be revealed.

All kidding aside, it’s a fun read about how a great number of Americanisms originated.

( Less VRS and SWP )
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Old 28th Nov 2017, 15:55
  #105 (permalink)  
 
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In Post #41, TC writes a fixed-wing analogy to SWP:
You are landing your jumbo jet at Heathrow and for that given AUM you decide to apply maximum reverse thrust to prevent yourself running off the runway. But all the reverse thrust available is not sufficient to arrest the AUM in time to keep it on the runway. Your engines aren't powerful enough (IN THE REMAINING DISTANCE OFFERED) to arrest your particular AUM.

It is an engine thang! Nothing to do with little green arrows/updraft/alpha.
And see, this is why we Americans seem to be confused. Our FAA would not attempt to put a silly name on such a thing other than "Pilot Stupidity." Running off the end of a too-short runway doesn't deserve it's own term of excusability, if you will. You exceeded the performance limitations of your aircraft, simple as that, next!

Getting into a situation in which you're making too steep of an approach or too fast of an approach and the engine does not have enough power to stop you at the bottom is *not* a phenomenon worthy of its own category. It's just a dumb thing to do. You might want to call it "settling with power," and that term certainly seems to fit because blaming things on an invisible boogeyman makes you feel better, but FOREVER we Yanks have called SWP "a condition in which the rotor is re-ingesting its own tip vortices."

Which is why the FAA uses the VRS and SWP terms interchangeably: For all intensive purposes they are the same thing in our book. To hijack one of the term (SWP) and make it mean something else is just...I dont' know...weird.
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Old 28th Nov 2017, 18:17
  #106 (permalink)  
 
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Originally Posted by FH1100 Pilot View Post
” but FOREVER we Yanks have called SWP "a condition in which the rotor is re-ingesting its own tip vortices."

Which is why the FAA uses the VRS and SWP terms interchangeably: For all intensive purposes they are the same thing in our book. To hijack one of the term (SWP) and make it mean something else is just...I dont' know...weird.
FH1100 has just helped me understand something - I was just about to make a smart Alec comment about “but Sir we’ve always said that the earth was flat” but then an epiphany; my understanding while following this thread was that the FAA was not differentiating between VRS & SWP because they didn’t acknowledge the difference, but reading FH1100’s post I now realise that the FAA understands that the rotor disc is reingesting it’s own vortices, they just call it SWP. Yes the disc is in a vortex ring state, they get that, but they refer to the condition based on what the aircraft is doing, not what the rotor disc is doing.

Did I get that right FH1100? It all makes sense to me now, I can relax & feel better knowing that the FAA aren’t aerodynamically challenged.
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Old 28th Nov 2017, 19:33
  #107 (permalink)  
 
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FH1100 - the problem is that what you call pilot stupidity causes lots of accidents and incidents.

When it comes to OGE hover performance, the military solution is to ensure an adequate thrust margin ie that you have more power available than is needed for hover OGE - that way you are unlikely to be embarrassed if you encounter slightly unfavourable conditions or don't fly so brilliantly.

To my knowledge, RFMs for civil aircraft don't include a percentage thrust margin graph, only an OGE hover graph for calculating MAUM for given pressure and temp conditions.

So, no problem as long as your maths and use of the graph are spot on - except that those graphs are for completely still conditions in a stable hover and don't take into account any turbulence or the fact that you need more power to get to the hover than you do to maintain it.

No wonder then that when extracting max performance from your aircraft (for whatever reason) you can get caught out and end up in a gentle descent with the lever up and the Nr slowly decaying (you are overpitching) - the solution is a gentle accel to gain speed.

Compare reacting correctly to this situation (because you know it is SWP and not VRS) to what would happen if you only thought SWP and VRS were the same and therefore had the same recovery ie dump the lever and try to get forward speed.

You can continue to pretend the FAA see-all and know-all but if they truly recognise the difference between running out of power and being in vortex ring, they should say it loud and clear to remove any confusion.
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Old 28th Nov 2017, 20:07
  #108 (permalink)  
 
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Instead the FAA handbook says this
Settling With Power (Vortex Ring State)
Vortex ring state 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 term “settling with power” comes from
the fact that the helicopter keeps settling even though full
engine power is applied.
talk about a wide spread of conditions and the misleading statement that would lead you to believe you have to have full power applied to be in VRS.
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Old 28th Nov 2017, 20:25
  #109 (permalink)  
 
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I guess I'm what they call "old school." Look, I learned to fly in a Bell 47 powered by a Franklin engine. In the summer. We spent a lot of time at WOT - literally wide-open throttle. You did NOT allow your engine/rotor rpm to droop on approach. Nobody taught us the modern term of "over-pitching." I guess that came with the Robbies.

By the same token, we learned quickly not to go into really tight or "hover-hole" LZ's where you might not be able to get back out even if you managed to not crash going in.

The thing about "SWP" (as we knew it) was the "disconnect" between the collective and the rate of descent. If you pulled up a bit and the helicopter went down faster, you were re-ingesting your own rotor vortices. Without that bit of evidence, you weren't in SWP. You still might not have enough power to stop at the bottom (if you couldn't get it into ground cushion before the skids hit), but that was your own screw-up, not that of the aircraft.

(Why any self-respecting pilot would continue to pull collective and bleed the rotor rpm down is beyond me. Rotor rpm is life. If you sacrifice it, it's your own damn fault.)

Same thing in governed, turbine helicopters. If moving the collective still modulates the rate of descent, then you're *not* in the FAA's version of SWP.

If you are at a power limit and the helicopter still keeps going down, then if you have the altitude you better get the hell out of there because something bad is about to happen; it's not going to get better. It doesn't matter at this point whether your vortices are above or below the rotor disk - you're about to crash.

Finally, I have never, ever heard of "SWP" being applied to a condition of flight when you're above ETL. If you come in fast, above ETL, and you don't for some reason have enough power to stop at the bottom, it's not SWP. It's you being a dumbass.
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Old 28th Nov 2017, 21:01
  #110 (permalink)  
 
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I think I finally see the real issue here? It looks like the Brits and Canadians feel that there aren't a lot of crashes due to entering the vortex ring state, so using the term "settling with power" to describe it, is kind of a waste of a perfectly good term, so they decided to repurpose it?

The problem is, in there incorrect use of these words!

If you have "run out of power" then its not "with power"!

If you have "run out of room", but can still slow down, it may still be "with power", but its not "settling"!

Perhaps you should spend more time teaching your pilots to start slowing down sooner, instead of coming up with names for what happens when they don't!

Sorry for coming back in, but I really had to pee! Besides, the mods probably won't even post this!
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Old 28th Nov 2017, 22:29
  #111 (permalink)  
 
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Butters
If you have "run out of power" then its not "with power"!
outstanding logic, no wonder you are struggling with this concept
If you have run out of power, you are at max power so it most certainly is 'with power'.

FH1100 -
If you are at a power limit and the helicopter still keeps going down, then if you have the altitude you better get the hell out of there because something bad is about to happen; it's not going to get better. It doesn't matter at this point whether your vortices are above or below the rotor disk - you're about to crash.
completely agree - it is just about recognising why and not trying to enter auto to get out of VRS when all you need is a few knots of airspeed to get above ETL again.

(Why any self-respecting pilot would continue to pull collective and bleed the rotor rpm down is beyond me. Rotor rpm is life. If you sacrifice it, it's your own damn fault.)
again, completely agree but, just like CFIT, supposedly self-respecting pilots seem to manage it.

Whatever we choose to call the scenarios - prevention is far better than cure in both cases but that is made more difficult if they are rolled in to one broad-brush term.

These are both conditions you or I would recognise instantly and recover appropriately and instinctively - plenty out there who wouldn't.
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Old 29th Nov 2017, 00:01
  #112 (permalink)  
 
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Originally Posted by [email protected] View Post
Butters outstanding logic, no wonder you are struggling with this concept
If you have run out of power, you are at max power so it most certainly is 'with power'.
Yes, the engine is running, and thus producing power, but by that logic you could call a normal landing, "settling with power"!

You've been banging your head against that wall too much!

The term "with power" means "with power available", not simply, with the engine running!

Being at max power by itself will not cause you to settle. However, if max power is not enough, then you will begin to settle due to a lack of additional "power available"! It is not called "settling with power" because you have no more power available!

If you did have more power available the only way you would start to settle is because you have entered the vortex ring state, which is why we call it settling "with power". You have power available, but are still settling!

Just when I think I'm out, they drag me back in!
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Old 29th Nov 2017, 00:16
  #113 (permalink)  
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To think this thread started discussing where old guys knew more than the book!

(Pull your pants up, Butters!)

There is a difference between SWP, "over-pitching" (whatever that is) and VRS. Each of these may be whatever the test-giver wants it to be. Give that answer.
Know what each is and have a plan to deal with eventualities as required to assure your survival when you are actually flying.

VRS? When the airspeed indicator bottoms out and the little orange yarn on the nose of an Astar starts dancing I have to be descending real, real slow. If it twitches or acts like it wants to twitch and that isn't part of my plan- abort and plan a better way in.

SWP? Know you're heavy and plan for a run-on or a fly out, and fly that profile. Or don't do it at all. It's easier to make a couple trips with an intact helo than it is to recover a broken one.

"Over-pitching"? Airplane drivers say "airspeed, altitude and ideas, never run out of one without lots of the others". Lack of NR makes it a moot point.
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Old 29th Nov 2017, 01:17
  #114 (permalink)  
 
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Originally Posted by Devil 49 View Post
(Pull your pants up, Butters!)
Now you know I can't do that Wally!

,...not until every helislave is free to take his lunch break!
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Old 29th Nov 2017, 03:32
  #115 (permalink)  
 
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One of the perfect example of SWP it is a few years ago a 747 Captain, freshly dual rated on helicopters . One day he fly with friends on an Alouette 2 ( turbine engine remember..) He check the weight and balance, check the abacus with Zp and OAT : everything is limit, but ok !
Full passengers, no doors but just at limit on the MTOW, smooth take off on the limit off power and climbing at 500 ft...few minutes later, one passengers ask him to make an hovering in front of his house to take picture.
The Captain say OK ! He slow the speed until stop at 300ft and....Surprise, the helicopter settling with power...and finish in a pond, nobody hurt ...

Why ?
He take off at the power limit IGE, In Ground Effect = Right !
Few minutes later and few liters of kerozen burned but not enough to change the chart......
He stop (try to stop ) his helicopter OGE : Out Ground Effect...FAULT ! he don't check the abacus for OGE, only IGE...
He was a young pilot on helicopter and don't feel the limit when he reach the hovering. If he can , it was easy to escape, just take some speed....
If you follow a French helicopter Course, you learn the hovering power difference between IGE and OGE is around 7% ( or 7% oflift weight capacity)
If you have the power to standard hovering ( 5 ft) IGE at 100%, that's really at the limit but enough for take off...BUT if you want to make an hovering OGE, you need 107% at the same place ( Zp/OAT ) and same load...
If you don't have the 7%....You go sure in SWP...
For sling or the hoist, if the charge weight augmentation exceed the max power available, you know it immediatly ! : the NG (turbine engine) NR ( piston engine) decrease, when you want to lift more than you can.
At this point you have 2 choice ! ....
You continue to increase the pitch and sure, you go down slowly....
OR
you decrease the pitch a little be , the NG/Nr increase and you reach the OGE hovering... your are safe. End of the story..
No one can talk about VRS, it's only a power story and abacus good reading ....
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Old 29th Nov 2017, 03:45
  #116 (permalink)  
 
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Finally, I have never, ever heard of "SWP" being applied to a condition of flight when you're above ETL. If you come in fast, above ETL, and you don't for some reason have enough power to stop at the bottom, it's not SWP. It's you being a dumbass.
Another occasion when I regret that PPRuNe doesn't have a "like" button!
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Old 29th Nov 2017, 07:34
  #117 (permalink)  
 
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No-one said SWP/VRS occurs above ETL................

Butters
Just when I think I'm out, they drag me back in!
feel free to stay out since you are either trying to wind people up or just don't understand helicopters very well.
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Old 29th Nov 2017, 08:16
  #118 (permalink)  
 
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Since TC makes such a fuss about the superiority of Transport Canada I looked up what they have to say:

There are some uninformed pilots who use “settling with power” to describe vortex ring, in fact some publications use the terms interchangeably. Confusion results when symptoms are related that do not describe true vortex ring but rather describe “settling with insufficient power”. This may occur when a pilot attempts to arrest a rapid, low power descent only to find that he has insufficient power available to bring the helicopter to either a hover or a no-hover landing without exceeding the engine limits. However, this is not a vortex ring situation.

Another situation, ‘over-pitching’ is often misinterpreted as vortex ring. This is where the pilot rapidly increases collective considerably and the engine cannot produce enough power to overcome the large, swift increase in drag on the rotor system. The result is that the rotor system quickly slows down and loses efficiency causing the helicopter instantly to sink. Again, this is not vortex ring.
Being called "uninformed" (or in plain English "stupid") is rather arrogant. I thought Canadians were so nice and polite?

Well apparently the Canucks have even more:
Settling with power is when a pilot can not arrest the sink rate after a RAPID, LOW POWER descent. What about a slow, high power flat descent where the pilot isn't able to hover either and falls on the landing spot, bending things giving enough height. That's not settling with power? Does the "may occur" mean, that this is one situation or this is THE situation but it does not always happen?

Over pitching is again something else. You can increase the collective slowly and still over- pitch. There is no need of a swift increase of drag. Anyway, nobody I can think of ever called that SWP nor VRS.

Anyway, after reading Transport Canadas view, I think, instead of having less confusion in the terms, there is even more.

After insulting everybody, they made it even worse.
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Old 29th Nov 2017, 10:02
  #119 (permalink)  
 
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Yes, they haven't really got the wording right at all.

In this sentence
This may occur when a pilot attempts to arrest a rapid, low power descent only to find that he has insufficient power available to bring the helicopter to either a hover or a no-hover landing without exceeding the engine limits. However, this is not a vortex ring situation.
they didn't need to put 'rapid, low power descent', just the word descent would have been clearer.

Similarly in the overpitching sentence, this
This is where the pilot rapidly increases collective considerably and the engine cannot produce enough power to overcome the large, swift increase in drag on the rotor system
doesn't need the words 'rapidly, considerably, large or swift' in it
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Old 29th Nov 2017, 10:06
  #120 (permalink)  
 
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So perhaps it should read
There are some pilots who use “settling with power” to describe vortex ring, in fact some publications use the terms interchangeably. Confusion results when symptoms are related that do not describe true vortex ring but rather describe “settling with insufficient power”. This may occur when a pilot attempts to arrest a descent only to find that he has insufficient power available to bring the helicopter to either a hover or a no-hover landing without exceeding the engine limits. However, this is not a vortex ring situation.

Another situation, ‘over-pitching’ is often misinterpreted as vortex ring. This is where the pilot increases collective and the engine cannot produce enough power to overcome the increase in drag on the rotor system. The result is that the rotor system slows down and loses efficiency causing the helicopter to sink. Again, this is not vortex ring.
Perhaps it could also add that overpitching is often experienced following the 'settling with insufficient power' as described in the first paragraph.
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