Vortex Ring / Settling with power (Merged)
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Hi ALL,
Been a while since I posted but here goes!
Nick, I read all your wisdom posted, but I feel a little reluctant to tell a newbie that "if your flying this type or that type" you wont have a problem with VRS.
My simple philosophy has always been and always will be, watch out, VRS WILL BITE YOU IN THE A$$ IF YOU LET IT.
But thats just me.
Cheers
OffshoreIgor
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The problem with believing and teaching the myth is that you teach the student to cure a performance problem (too little HOGE power margin) by not descending. Sort of like telling a guy who is playing with dynamite to use earplugs.
The vast majority of mythical VRS stories are experienced by folks who hovered OGE with too little power margin, settled down and scared the crap out of themselves. It is impossible to get VRS in a helo with high power margins, unless you go down so fast vertically that you deserve to die.
Teach students to have 10% power margin before they hover OGE. Teach students that VRS will happen if they descend at more than 700 to 1000 feet per minute. Then you are teaching the truth, and in a way that will prevent accidents, not explain them.
The vast majority of mythical VRS stories are experienced by folks who hovered OGE with too little power margin, settled down and scared the crap out of themselves. It is impossible to get VRS in a helo with high power margins, unless you go down so fast vertically that you deserve to die.
Teach students to have 10% power margin before they hover OGE. Teach students that VRS will happen if they descend at more than 700 to 1000 feet per minute. Then you are teaching the truth, and in a way that will prevent accidents, not explain them.
Nick said
"It is impossible to get VRS in a helo with high power margins, unless you go down so fast vertically that you deserve to die."
Before we go any farther here, just how much long line time do you have? Do you consider a Lama with 60 gallons of fuel and no load to have adequate power margins?
"It is impossible to get VRS in a helo with high power margins, unless you go down so fast vertically that you deserve to die."
Before we go any farther here, just how much long line time do you have? Do you consider a Lama with 60 gallons of fuel and no load to have adequate power margins?
At 8,000 feet MSL, 25 degrees Canadian and 60 gallons of fuel the Lama is capable of climing and decending vertically with 1,500 lb loads. With no load the verticle rate of climb is better than 2,500 feet per minute. Nobody that has ever flown a Lama has considered it under powered.
I have never gotten into "settling" with a load on. I have had loads that I could not hold and have had to let them land so I could regroup. Apparently I am more careful with a load on than with an empty hook.
I have never gotten into "settling" with a load on. I have had loads that I could not hold and have had to let them land so I could regroup. Apparently I am more careful with a load on than with an empty hook.
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What is the power to hover OGE and what is the max power and what is the gross weight (without the 1500 lb load that it can handle?)
What is the power margin with the 1500 lb load HOGE?
What is the power margin with the 1500 lb load HOGE?
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Can I ask a related question pls? We have a huge amount of questions at work with conflicting answers between the web and the manufacturer. We just started operating an EC130. Can the fenestrom stall or get vortex ring/LTE? What would be the warning and rectification or prevention? Sorry if I diverted!!!!
Nick
I'm at work and my Lama manual is at home. I will jpg the IGE and OGE charts to you tonight. But if the aircraft can handle a 1.500 pound load in those conditions it stands to reason that it has more than adequate power without the load. The seismic and core drills that I moved were broken down into 1,200-1,500 loads. The Lama moved them day in and day out.
But before we get too far into Lama peformance I have had the same phenomonen in the UH-1H with the 1,800 hp engine, the Hughes 500D, and the Jet Ranger series. It is not machine specific. Ask any logging pilot and they will tell you that they make their money at the edge of settling.
I'm at work and my Lama manual is at home. I will jpg the IGE and OGE charts to you tonight. But if the aircraft can handle a 1.500 pound load in those conditions it stands to reason that it has more than adequate power without the load. The seismic and core drills that I moved were broken down into 1,200-1,500 loads. The Lama moved them day in and day out.
But before we get too far into Lama peformance I have had the same phenomonen in the UH-1H with the 1,800 hp engine, the Hughes 500D, and the Jet Ranger series. It is not machine specific. Ask any logging pilot and they will tell you that they make their money at the edge of settling.
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The symptoms of vortex ring state can be encountered any time the downwash velocity equals or is very close to the rate of descent.
As the downwash velocity will vary along the span of the rotor blade, the symptoms can be encountered in more conditions than just the absolute classical case.
When entering using the method I described (much) earlier, the downwash velocity is initially pretty low, because you're at a reduced power setting. As you start to descend (due to power used being less than power required to maintain a hover), you may be in a (dare I introduce a term here) partial vortex ring state - that's what makes the demonstration not totally repeatable. If, as you start to descend, you were able to match the average downwash velocity from the rotor, you'd have the classical 'total' vortex ring state.
I've never been lucky (?) enough to get that to happen in all the demonstrations I've done, but the symptoms that show up are sufficiently convincing that all the pilots I've done this with have said they've come away with a better understanding of the scenario.
To recap - anytime the downwash velocity equals the rate of descent you should encounter (some of) the symptoms of vortex ring state. Learn those and either avoid the situation if possible, or know when and how to get out it.
As the downwash velocity will vary along the span of the rotor blade, the symptoms can be encountered in more conditions than just the absolute classical case.
When entering using the method I described (much) earlier, the downwash velocity is initially pretty low, because you're at a reduced power setting. As you start to descend (due to power used being less than power required to maintain a hover), you may be in a (dare I introduce a term here) partial vortex ring state - that's what makes the demonstration not totally repeatable. If, as you start to descend, you were able to match the average downwash velocity from the rotor, you'd have the classical 'total' vortex ring state.
I've never been lucky (?) enough to get that to happen in all the demonstrations I've done, but the symptoms that show up are sufficiently convincing that all the pilots I've done this with have said they've come away with a better understanding of the scenario.
To recap - anytime the downwash velocity equals the rate of descent you should encounter (some of) the symptoms of vortex ring state. Learn those and either avoid the situation if possible, or know when and how to get out it.
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Nick Lappos: As a CFI I am interested in how you personally would teach VRS/SWP in a single engine piston helicopter? How would you explain it to a newbie student, what points would you emphasise? How would you fly the demo?
I teach this 'maneuver' a lot and I would welcome your opinion
I teach this 'maneuver' a lot and I would welcome your opinion
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manfromuncle,
Good question, it is easy to comment on what we do, harder to say what we should do!
Let me start out by saying the lesson is OGE hover safety, and the lesson has two different, and equally important pieces, Performance and VRS. I would bet 95% of all hover descent accidents are the result of performance /overpitching and NOT VRS:
1) Hover PERFORMANCE
A) where the power needs of OGE vice IGE are discussed and demonstrated (use a light helo, and trim IGE, note power, then trim OGE and note power. Pick 3 IGE hover heights and then plot the power post-flight. Look up OGE performance in the RFM to orient the pilot to the weight effects. Then discuss altitude temperature and wind effects.
B) Then discuss marginal OGE hover, and the insidious danger of over-pitching, especially how the rpm decay leads to even lower power so that the fall is accelerated.
C) Then discuss how low rpm leads to Loss of Tail Rotor Control.
D) Then show how an OGE descent at moderate rate can be flown up if one has some good power reserves to just raise the collective. The point to be made is that one can descend at 300 or 500 fpm in any helicopter with sufficient power reserves, and simply raise collective and fly up out of the descent. This is known to all military pilots when they operate NOE, and is not a mystery. The student should be shown, however, that a descent needs somewhat MORE power than a steady HOGE, so that a 300 FPM descent will need about 5% more power than a steady hover. (This is the fact that fuels the "VRS" demos we all are shown, and the reason why descents lead to overpitching).
2) Vortex Ring State
A) At 3000 feet or higher, slow to a steady OGE hover. Begin a descent at moderate vertical speed and accelerate the descent until you are at 75% of the downwash speed. (I can show how to calculate this for any helo). At this ROD note the lurches as the thrust bucks by +10%, and the aircraft has torque surges of 10 to 20%. This is incipient VRS, and all that is necessary to show, fly out of it by lowering the nose to accelerate and break the reingestion that is feeding the VRS. The lesson is vastly different that the above OGE power lesson.
Good question, it is easy to comment on what we do, harder to say what we should do!
Let me start out by saying the lesson is OGE hover safety, and the lesson has two different, and equally important pieces, Performance and VRS. I would bet 95% of all hover descent accidents are the result of performance /overpitching and NOT VRS:
1) Hover PERFORMANCE
A) where the power needs of OGE vice IGE are discussed and demonstrated (use a light helo, and trim IGE, note power, then trim OGE and note power. Pick 3 IGE hover heights and then plot the power post-flight. Look up OGE performance in the RFM to orient the pilot to the weight effects. Then discuss altitude temperature and wind effects.
B) Then discuss marginal OGE hover, and the insidious danger of over-pitching, especially how the rpm decay leads to even lower power so that the fall is accelerated.
C) Then discuss how low rpm leads to Loss of Tail Rotor Control.
D) Then show how an OGE descent at moderate rate can be flown up if one has some good power reserves to just raise the collective. The point to be made is that one can descend at 300 or 500 fpm in any helicopter with sufficient power reserves, and simply raise collective and fly up out of the descent. This is known to all military pilots when they operate NOE, and is not a mystery. The student should be shown, however, that a descent needs somewhat MORE power than a steady HOGE, so that a 300 FPM descent will need about 5% more power than a steady hover. (This is the fact that fuels the "VRS" demos we all are shown, and the reason why descents lead to overpitching).
2) Vortex Ring State
A) At 3000 feet or higher, slow to a steady OGE hover. Begin a descent at moderate vertical speed and accelerate the descent until you are at 75% of the downwash speed. (I can show how to calculate this for any helo). At this ROD note the lurches as the thrust bucks by +10%, and the aircraft has torque surges of 10 to 20%. This is incipient VRS, and all that is necessary to show, fly out of it by lowering the nose to accelerate and break the reingestion that is feeding the VRS. The lesson is vastly different that the above OGE power lesson.
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Someone smarter than me feel free to correct, but it seems to be a question of momentum. Taking off from a confined area, where your obstacle is at OGE height, you can get out with less than OGE power if you apply power early to gain an upward momentum and "coast" over the obstacle. The reverse is true, your downward momentum requires extra power to stop. If you start in an OGE hover of say 200ft, and descend at 500fpm with the intention of stopping at 100ft while still OGE, you will need greater than OGE power. How much extra power you need will depend on your decent rate and how much you weigh. I don't remember off the top of my head but I think the HAATS number for a Blackhawk is every 100fpm of decent rate requires 2% of excess power to arrest. If I'm right, it is easy to see how going from one OGE height to another with only OGE available could get hairy.
EDIT: What I'm talking about is a crappy situation that is not VRS but could make you think it was.
EDIT: What I'm talking about is a crappy situation that is not VRS but could make you think it was.
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The point that we are all working around is that power problems in OGE are usually NOT Vortex Ring State, and that 300 fpm descents in the hover are not by themselves dangerous.
Here is a web site that does a credible job of discussing VRS:
http://www.safetycenter.navy.mil/MED...n03/vortex.htm
Here is a diagram from it, the values are quite valid for light helicopters. Note that it is NOT POSSIBLE to even feel slight VRS at descent rates less than about 750fpm, and full blown VRS requires 1000 fpm:
Here is a web site that does a credible job of discussing VRS:
http://www.safetycenter.navy.mil/MED...n03/vortex.htm
Here is a diagram from it, the values are quite valid for light helicopters. Note that it is NOT POSSIBLE to even feel slight VRS at descent rates less than about 750fpm, and full blown VRS requires 1000 fpm:
Nick
I ask again what your production long line experience is? The phenomenon is there at low power settings, low speed and low rates of decent. I and every other long line pilot I know has experienced it. Is this just anecdotal evidence in a scientific world?
I ask again what your production long line experience is? The phenomenon is there at low power settings, low speed and low rates of decent. I and every other long line pilot I know has experienced it. Is this just anecdotal evidence in a scientific world?
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lama bear,
I am not sure what you experience but at low rod it is not VRS. Can you tell us what you experience, in as much detail as you can?
I looked at the charts you sent, and they indicate that at moderate altitudes at 2500 lbs the Lama has no power issues at all, it is a screamer, so it is not "over pitching" for sure.
For the record, I have not worked long line, ever. That being said, I have done one heck of a lot of tethered hover, sling loads and OGE Height Velocity engine cut testing. I do not at all doubt your experience, sincerity and capability, lama, just that what you are experiencing is VRS (unless you are descending at 1000 fpm.)
I am not sure what you experience but at low rod it is not VRS. Can you tell us what you experience, in as much detail as you can?
I looked at the charts you sent, and they indicate that at moderate altitudes at 2500 lbs the Lama has no power issues at all, it is a screamer, so it is not "over pitching" for sure.
For the record, I have not worked long line, ever. That being said, I have done one heck of a lot of tethered hover, sling loads and OGE Height Velocity engine cut testing. I do not at all doubt your experience, sincerity and capability, lama, just that what you are experiencing is VRS (unless you are descending at 1000 fpm.)
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In a previous VRS discussion someone thought he had encountered VRS while hovering beside a ridge top in an updraft.
My understanding was hovering in a 1000ft/min updraft = 1000ft/min descent and possible VRS.
My understanding was hovering in a 1000ft/min updraft = 1000ft/min descent and possible VRS.
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I would seriously doubt that the precise angle of descent and steady flow into the rotor to cause VRS could be found in a mountain updraft. At least not enough to cause any loss of sleep over the possibility.
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Lama Bear, is there any chance that ground effect vortex roll up might be causing some downwash to be recirculated? It sounds to me like what you are describing only happens at the start of ground effect. It might be something new...
Nick, my ABS once again stepped in this morning to catch a nasty moment on a spot of unexpected road ice. For settling with power there must surely be an arguement for parallel and series actuators in the collective. The wee computer would stop a nasty moment becoming anything more...
Nick, my ABS once again stepped in this morning to catch a nasty moment on a spot of unexpected road ice. For settling with power there must surely be an arguement for parallel and series actuators in the collective. The wee computer would stop a nasty moment becoming anything more...