Vortex Ring / Settling with power (Merged)
pcpahari_IAF
pcpahari_IAF, could you use the "quote" tags rather than the "code" tags to display quoted text? It makes for easier reading.
The "code" button is the # symbol. The "quotes" button is the one to the left. Thanks.
The "code" button is the # symbol. The "quotes" button is the one to the left. Thanks.
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Ramen Noodles,
I can tell you that it is possible to get into V.R. with zero rate of descent if the wind is flowing upslope, actually incipient VR is probably a more accurate term.
The conditions have to be just right and it a very rare occurrence, but it does happen.
There are many a longline pilot here in Canada that has spent years and literally thousands of hours hovering at 100-200 feet over steep hill/cliffs. On a rare occasion when all the planets align if you come into a hover on the edge of a cliff on windy days, it has the potential to get nasty in a hurry.
When I am hovering over a spot that I know is going to give me VRS problems, if I can get the empty hook into the spot and pick up the load I never have a problem flying away with it. This relates back to the Nicks statements on the light vrs heavy theory, he is correct.
I can tell you that it is possible to get into V.R. with zero rate of descent if the wind is flowing upslope, actually incipient VR is probably a more accurate term.
The conditions have to be just right and it a very rare occurrence, but it does happen.
There are many a longline pilot here in Canada that has spent years and literally thousands of hours hovering at 100-200 feet over steep hill/cliffs. On a rare occasion when all the planets align if you come into a hover on the edge of a cliff on windy days, it has the potential to get nasty in a hurry.
When I am hovering over a spot that I know is going to give me VRS problems, if I can get the empty hook into the spot and pick up the load I never have a problem flying away with it. This relates back to the Nicks statements on the light vrs heavy theory, he is correct.
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Not to sure about all the aerodynamics but I am sure that if you have much low level experience its hard to confuse SWP and VRS.
Pre R22 govenor days it was not unusual to encounter SWP when low level hot and heavy so much so that it was standard (in Oz) to teach students to milk the Col and throttle to restor RRPM
My experience is that SWP will involve reducing RRPM and increasing everything else, whereas VRS will have increasing everything else (apart from IAS) and RRPM OK
Also in my experience it is very easy to induce VRS in light ac with light AUW. Just gain some Alt lose your IAS turn down wind initiate a rate of descent and pull some pwr then watch the ROD go off the clock.
Of course in real life we should know when we are potentially at risk and be ready to correct if we feel the onset of VRS, prior to it becoming fully developed.
I would hope this is still being covered in basic training
No idea about the heavies most of you seem to fly
Cheers
Pre R22 govenor days it was not unusual to encounter SWP when low level hot and heavy so much so that it was standard (in Oz) to teach students to milk the Col and throttle to restor RRPM
My experience is that SWP will involve reducing RRPM and increasing everything else, whereas VRS will have increasing everything else (apart from IAS) and RRPM OK
Also in my experience it is very easy to induce VRS in light ac with light AUW. Just gain some Alt lose your IAS turn down wind initiate a rate of descent and pull some pwr then watch the ROD go off the clock.
Of course in real life we should know when we are potentially at risk and be ready to correct if we feel the onset of VRS, prior to it becoming fully developed.
I would hope this is still being covered in basic training
No idea about the heavies most of you seem to fly
Cheers
Aucky - I don't think there is anything wrong with your understanding of VRS but you are forgetting that at high AUM and therefore higher pitch and AoA settings, you are displacing air faster downwards than at lightweights - therefore you must have to descend faster to catch your downwash. This is what Nick has always tried to emphasise, it is all about downwash velocity - a helo of a given AuM with a high disc loading will have a higher downwash velocity than one with a lower disc loading.
You have to move enough air fast enough downwards to balance the mass of the helo and you can do it with a big disc with a large input area imparting a modest acceleration or a small disc working harder with a smaller input area and imparting a larger acceleration.
You have to move enough air fast enough downwards to balance the mass of the helo and you can do it with a big disc with a large input area imparting a modest acceleration or a small disc working harder with a smaller input area and imparting a larger acceleration.
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code vs quote
Apologies to everybody for the ill-formatted post. Am new to forum participation... Still learning.
To MightyGEM
Thankyou for the inputs But..
I wanted to do the same Didn't know how?
Still not clear.
Req more details as to how to paste quoted text as quotes.)
-Thanx in anticipation.
To MightyGEM
Thankyou for the inputs But..
I wanted to do the same Didn't know how?
Still not clear.
Req more details as to how to paste quoted text as quotes.)
-Thanx in anticipation.
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I wanted to do the same Didn't know how
magic.
cheers mate I had to ask heliport how to not so long ago.
Thankyou
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To: Crab and Aucky & All the experts
As you can see... its Light or Heavy again... 
(Please refer my query earlier and Auckys post dated 15 Aug).
The RAF Manual on rotordynamics also explains Vortex Ring as outlined by Aucky's 15 Aug Post
.
While I am personally convinced about Vortex ring being a purely Aerodynamic phenomenon resultin from interaction of the tip vortices to intensify with increasing ROD (Opposing Relative Flow) and induced flow produced by the rotors (powered rotor motion) ultimately settling the helicopter into this wake such that increasing power (coll) only intensifies the vortices at the tips causing the hepter to descend at an even increasing rate. I am in agreement with the finer aspects of winds and the fwd speed (relative) vividly brought out all throughout the posts in this forum however, I request the old hands to re-read Aucky's post... (with emphasis on the aspect of root end being stalled and insifying vortices at tips...&.. this state occuring earlier in Heavy hepters). Request point out where and how such an analogy would be wrong.... Thats the question my folks here have been arguing...
Thanks yet again
(Please refer my query earlier and Auckys post dated 15 Aug).The RAF Manual on rotordynamics also explains Vortex Ring as outlined by Aucky's 15 Aug Post
.While I am personally convinced about Vortex ring being a purely Aerodynamic phenomenon resultin from interaction of the tip vortices to intensify with increasing ROD (Opposing Relative Flow) and induced flow produced by the rotors (powered rotor motion) ultimately settling the helicopter into this wake such that increasing power (coll) only intensifies the vortices at the tips causing the hepter to descend at an even increasing rate. I am in agreement with the finer aspects of winds and the fwd speed (relative) vividly brought out all throughout the posts in this forum however, I request the old hands to re-read Aucky's post... (with emphasis on the aspect of root end being stalled and insifying vortices at tips...&.. this state occuring earlier in Heavy hepters). Request point out where and how such an analogy would be wrong.... Thats the question my folks here have been arguing...
Thanks yet again
Pcpahari - I think what you are asking is :
Does the heavier helicopter operating at higher pitch angles to hover reach a blade stall at the root earlier in a descent than a lighter helicopter?
I think the simplistic explanation of the flow around the tips and roots of the blades given in the RAF manual and others may be an outdated version of events which have subsequently been shown in more detail by better modelling and testing.
Nick's sources imply that VRS can be overcome with power if there is sufficient available which would indicate that intensification of the tip votices and extensive stalling of the roots doesn't happen.
Remember that the older manuals and explanations were created in the days of underpowered helos which had low disc loadings because of the low engine power. It may be that the 'intensification' of VRS was just overpitching as the aircraft ran out of power or that the older aerofoil sections on wooden or metal blades were not as efficient as modern, composite blades with cambered sections.
I am sure the TPs on this forum will have more to add.
Does the heavier helicopter operating at higher pitch angles to hover reach a blade stall at the root earlier in a descent than a lighter helicopter?
I think the simplistic explanation of the flow around the tips and roots of the blades given in the RAF manual and others may be an outdated version of events which have subsequently been shown in more detail by better modelling and testing.
Nick's sources imply that VRS can be overcome with power if there is sufficient available which would indicate that intensification of the tip votices and extensive stalling of the roots doesn't happen.
Remember that the older manuals and explanations were created in the days of underpowered helos which had low disc loadings because of the low engine power. It may be that the 'intensification' of VRS was just overpitching as the aircraft ran out of power or that the older aerofoil sections on wooden or metal blades were not as efficient as modern, composite blades with cambered sections.
I am sure the TPs on this forum will have more to add.
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I'm reminded that a test pilot for one of the manufacturers told me (many many years ago):
"You can't get into vortex ring state in this helicopter because if you pull maximum power you can get out it..."
"You can't get into vortex ring state in this helicopter because if you pull maximum power you can get out it..."
"You can't get into vortex ring state in this helicopter because if you pull maximum
Shawn, also many many years ago, I was pax in a Bell 214 B, lightly loaded, steep downwind approach. Pilot looked at me and said "Don't worry about it, this thing has got so much power, it just doesn't make any difference."
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I think that if you look at this thread (below) and some other related ones that you will get the impression that the statement "using heaps of power will pull them out of VRS", is Fallacious.
http://www.pprune.org/rotorheads/280...wk+vortex+ring
I have no doubt that many pilots who had never got right into VRS thought that it was power that pulled them out anytime, and maybe the story has mistakenly gone the rounds or many briefing rooms.
I know also that elswhere on pprune that we have discussed the phenomina of being able able to "flick it out" with a quick pull on the collective before VRS actually develops to the 'sphinter (spelling?)tightening' stage.
That techniques has nothing to do with power, but everything to do with awareness, reactions, and plenty of pre-emptive training, and just quietly, being able to get the damm collective down again real quick like.
I believe the technique carried strong endorsement from many experienced types here at the time. I just want to impress on newbies that it is fraught with disaster if you think that you will rely upon it without the right training.
It reminds me of an article in one our CASA safety digests many years ago, headlined; 'Mustering is for the highly trained'.
So don't do this sort of thing with your family car I say. seek help to explain, it's out there.
cheers tet
http://www.pprune.org/rotorheads/280...wk+vortex+ring
I have no doubt that many pilots who had never got right into VRS thought that it was power that pulled them out anytime, and maybe the story has mistakenly gone the rounds or many briefing rooms.
I know also that elswhere on pprune that we have discussed the phenomina of being able able to "flick it out" with a quick pull on the collective before VRS actually develops to the 'sphinter (spelling?)tightening' stage.
That techniques has nothing to do with power, but everything to do with awareness, reactions, and plenty of pre-emptive training, and just quietly, being able to get the damm collective down again real quick like.
I believe the technique carried strong endorsement from many experienced types here at the time. I just want to impress on newbies that it is fraught with disaster if you think that you will rely upon it without the right training.
It reminds me of an article in one our CASA safety digests many years ago, headlined; 'Mustering is for the highly trained'.
So don't do this sort of thing with your family car I say. seek help to explain, it's out there.
cheers tet
Tet - your link has far less to do with VRS than it does about mishandling when approaching downwind. It would appear that he simply ran out of power and didn't have enough height, speed or power to go around.
No-one is suggesting that trying to power out of VRS is the way forward - simply saying that according to the windtunnel and airflow tests, this can be achieved if you have enough power available and use it - chances are you won't have enough and will only apply full power too late to save you hitting the ground/sea.
No-one is suggesting that trying to power out of VRS is the way forward - simply saying that according to the windtunnel and airflow tests, this can be achieved if you have enough power available and use it - chances are you won't have enough and will only apply full power too late to save you hitting the ground/sea.
And whatever you do.................................
don't fly over Burning Man!
or anywhere in Japan!
or anywhere in Japan!
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I suppose a "simple" explanation for "powering out of Vortex Ring State" is that if you accept VR to be the state when RoD ~= Induced Flow,
and,
RoD less than Induced Flow or significantly greater than Induced Flow (so vortices are lifted above and clear of the disc) to not be states of VRS,
then
It is conceivable for the scenario where you are in VRS (or early stages there of) that if you have the power (and rpm and angle of attack (until blade stall)) margin then you could create the induced flow to the point where it is greater than your RoD and put you back on top of the vortices (as apposed to keeping you in them).
The disclaimer being there are a lot of "ifs" in the above statement.
The Wagtendonk book has a pretty good section on the physics of VRS, including an interesting graph (Figure 19-6) of Effect of Airspeed and RoD on conditions required for VRS.
and,
RoD less than Induced Flow or significantly greater than Induced Flow (so vortices are lifted above and clear of the disc) to not be states of VRS,
then
It is conceivable for the scenario where you are in VRS (or early stages there of) that if you have the power (and rpm and angle of attack (until blade stall)) margin then you could create the induced flow to the point where it is greater than your RoD and put you back on top of the vortices (as apposed to keeping you in them).
The disclaimer being there are a lot of "ifs" in the above statement.
The Wagtendonk book has a pretty good section on the physics of VRS, including an interesting graph (Figure 19-6) of Effect of Airspeed and RoD on conditions required for VRS.
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Sorry to dig this back out again, but I was pondering on it again today.
Would it be reasonable to generalise this in the following way (differentiating between 'settling with power' & VRS):
'Settling with power' is more likely to occur when hot, high, heavy. These factors are more likely to lead to a situation whereby on an approach, with loss of translational lift, you develop an increasing ROD (if you don't regain TX lift), with power applied (probably over-pitch & low rpm) and low airspeed. This perhaps turns into fully developed VRS if there is sufficient height for ROD to develop before ground contact, but even without VRS developing this could be misinterpreted as actual VRS
(therefore the heavier the more likely)
However, to enter VRS without the cause being a lack of power induced ROD (perhaps just a bad out of wind approach etc), one needs a higher ROD when heavier because the speed of the downwash from the disc is greater and therefore you need a higher ROD to catch up with it... (going against the blade root stall etc... explanations that I was taught, but apparently true according to the real test data given by Nick, Shawn etc....) This is therefore more likely to occur accidentally at a lower AUM, given the required ROD may be less...
Does that sound reasonable as I often get asked on this because there is so much confusion between VRS and 'Settling with power'. Or is it me thats confused
Aucky
Would it be reasonable to generalise this in the following way (differentiating between 'settling with power' & VRS):
'Settling with power' is more likely to occur when hot, high, heavy. These factors are more likely to lead to a situation whereby on an approach, with loss of translational lift, you develop an increasing ROD (if you don't regain TX lift), with power applied (probably over-pitch & low rpm) and low airspeed. This perhaps turns into fully developed VRS if there is sufficient height for ROD to develop before ground contact, but even without VRS developing this could be misinterpreted as actual VRS
(therefore the heavier the more likely)However, to enter VRS without the cause being a lack of power induced ROD (perhaps just a bad out of wind approach etc), one needs a higher ROD when heavier because the speed of the downwash from the disc is greater and therefore you need a higher ROD to catch up with it... (going against the blade root stall etc... explanations that I was taught, but apparently true according to the real test data given by Nick, Shawn etc....) This is therefore more likely to occur accidentally at a lower AUM, given the required ROD may be less...
Does that sound reasonable as I often get asked on this because there is so much confusion between VRS and 'Settling with power'. Or is it me thats confused
Aucky
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Aucky, I think you've got it. In fact, I would bet that virtually all VRS events are SWP events, since very few involve rates of descent anywhere near that needed to induce flow reingestion.
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Aucky,
I kind of like the summary, only would refine :
Quote: "This perhaps turns into fully developed VRS if there is sufficient height for ROD to develop before ground contact, but even without VRS developing this could be misinterpreted as actual VRS (therefore the heavier the more likely)"
Into: One of the outcomes of settling with power can be VRS if an important increase of ROD develops. In most cases due to close proximity of the ground, this will not be the case.
wow, other effects of loss of RPM, ranging from LTE up to main rotor stall can also be expected.
m2c
d3
I kind of like the summary, only would refine :
Quote: "This perhaps turns into fully developed VRS if there is sufficient height for ROD to develop before ground contact, but even without VRS developing this could be misinterpreted as actual VRS (therefore the heavier the more likely)"
Into: One of the outcomes of settling with power can be VRS if an important increase of ROD develops. In most cases due to close proximity of the ground, this will not be the case.
wow, other effects of loss of RPM, ranging from LTE up to main rotor stall can also be expected.
m2c
d3