Vuichard technique for settling with power?
FICH that is full VRS and that will take a lot of height to recover from.
As you say it is best recognised and avoided
As you say it is best recognised and avoided
FICH that is full VRS and that will take a lot of height to recover from.
Have you ever tried it?
I will try film it for you, next time i do that with a student!
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Tim Tucker writes that as he teaches or demonstrates the Vuichard technique, "I frequently allow a high descent rate to build prior to initiating the recovery to clearly show how efficient this new technique really is."
So that's clearly not IVRS. Maybe can only be done in a Robbie?
So that's clearly not IVRS. Maybe can only be done in a Robbie?
With regard to the VT, let's remember one or two things.
First, for SWP/VRS to occur the helicopter will most assuredly be below ETL. So its ground-track (if any) will be slow. Let's assume it's traveling forward slightly and not coming straight down when the pilot experiences the dreaded IVRS.
Pushing the cyclic to the right while simultaneously pushing the left pedal will *not* result in the helicopter sliding perpendicular to the ground track. No, the helicopter will yaw to the left and the helicopter will probably continue along the previous ground track or approximately so. The combination of right cyclic and left pedal would then have the same effect as lowering the nose, but with the added benefit of thrust from the tail rotor.
I've thought and thought and thought about the Vuichard Technique, trying to come up with something meaningful to say one way or the other. I mean, I've been flying these things for a long, long time so you'd think I'd have learned something by now.
Initially I was predisposed to reject the VT out of hand. However it appears that I've learned something new.
First, for SWP/VRS to occur the helicopter will most assuredly be below ETL. So its ground-track (if any) will be slow. Let's assume it's traveling forward slightly and not coming straight down when the pilot experiences the dreaded IVRS.
Pushing the cyclic to the right while simultaneously pushing the left pedal will *not* result in the helicopter sliding perpendicular to the ground track. No, the helicopter will yaw to the left and the helicopter will probably continue along the previous ground track or approximately so. The combination of right cyclic and left pedal would then have the same effect as lowering the nose, but with the added benefit of thrust from the tail rotor.
I've thought and thought and thought about the Vuichard Technique, trying to come up with something meaningful to say one way or the other. I mean, I've been flying these things for a long, long time so you'd think I'd have learned something by now.
Initially I was predisposed to reject the VT out of hand. However it appears that I've learned something new.
No, the helicopter will yaw to the left and the helicopter will probably continue along the previous ground track or approximately so.
You must not allow the helicopter to yaw!
FH1100: I think you've got traction there, but only just.
What I think you are saying is that DURING IVRS, the VT has merit. If this is correct, I happen to agree with you.
Where I think the problems lie, are as follows:
1. People who describe the VT as a panacea to fully developed VRS, clearly do not understand the situation they are describing.
2. A lot of people do not understand the difference between IVRS and FDVRS.
3. During FDVRS, the cyclic will not do what you ask of it.
4. Ab initio's and clearly low timers (possibly others) have never been shown IVRS or how to recover, other than by word of mouth or in a book.
PS: Be careful mentioning SWP! A different ball park and almost certainly too late to employ the VT, I would suggest!
What I think you are saying is that DURING IVRS, the VT has merit. If this is correct, I happen to agree with you.
Where I think the problems lie, are as follows:
1. People who describe the VT as a panacea to fully developed VRS, clearly do not understand the situation they are describing.
2. A lot of people do not understand the difference between IVRS and FDVRS.
3. During FDVRS, the cyclic will not do what you ask of it.
4. Ab initio's and clearly low timers (possibly others) have never been shown IVRS or how to recover, other than by word of mouth or in a book.
PS: Be careful mentioning SWP! A different ball park and almost certainly too late to employ the VT, I would suggest!
Since we are so nicely going around in circles and FICH is rather frustrated with us not getting it.
The one for the R22
Just for arguments sake, can we agree on the area with light turbulence and thrust variation as IVRS, and the dark area is FDVRS?
In that case: I believe that no many of us have ever experienced FDVRS. All we talk about is IVRS. Charts for other helicopters are similar.
If you go straight down, you are in IVRS, not FDVRS, when you descend with 40 degrees, neither. And after a while you drop out of VRS at the bottom.
Now what are we talking about? Is it really that important, to get out of VRS or IVRS as fast as possible. The goal one has as an instructor is to teach students to use superior skill in judgement, so that they don't have to use superior piloting skill.
Let's assume the Vulcan Technique works as advertised. Great! Cool! How much better? Somebody should find out with calibrated instruments and a series of VRS test flights. Would be an interesting paper for a aeronautical engineering student.
As soon as the pilot feels the low frequency airframe vibration and the trust variation, he/she should take action. The these indications must not necessarily come from VRS. It might be just the loss of ETL and some SWP. In which case VT would not save the day.
A down draft in the lee of a mountain isn't VRS, but it might feel quite similar.
To show different techniques to students is a great thing and letting develop a high sink rate and getting out of it, is something every student should know, but I believe that this is more a demonstration of the awkward aerodynamics of the helicopter than something useful in everyday life.
"All those terrible accidents" that FICH stated, do not happen. They are rather few and far between. VRS accidents are not on "most wanted" list of aviation authorities in the world. That's probably just because the training works pretty well to avoid the shaded area in the first place. When you have to use the Vulcan Technique to get you out of a desperate situation, you have already pretty much ****** it up before.
One thing might speak in favour of the Vulcan Technique. The two accident reports I found which suspect VRS stated that the pilot tried to arrest the sink rate by adding power; the natural reaction but makes it worse. A bit of uncoordinated flight or only stick forward might have saved the day here. Apparently the pilots didn't realise that they were in VRS.
The conclusion would be: show the students the Vulcan, but hammer it into their brain, to avoid VRS and if they get low frequency vibration and thrust variations, don't try to salvage an approach by just adding power and flying uncoordinated. Start again. Go around. Speed up. It might have been something else than VRS. It is easy to identify something when you want it to happen. It is much harder, if it surprises you.
It is an additional tool for the (advanced) pilot, but it is not the ultimate thing one would use in panic mode and it isn't universal. In a French of Russian helicopter you must reverse the movements. That just does not work for a standard emergency technique. Keep it stupid and simple.
The one for the R22
Just for arguments sake, can we agree on the area with light turbulence and thrust variation as IVRS, and the dark area is FDVRS?
In that case: I believe that no many of us have ever experienced FDVRS. All we talk about is IVRS. Charts for other helicopters are similar.
If you go straight down, you are in IVRS, not FDVRS, when you descend with 40 degrees, neither. And after a while you drop out of VRS at the bottom.
Now what are we talking about? Is it really that important, to get out of VRS or IVRS as fast as possible. The goal one has as an instructor is to teach students to use superior skill in judgement, so that they don't have to use superior piloting skill.
Let's assume the Vulcan Technique works as advertised. Great! Cool! How much better? Somebody should find out with calibrated instruments and a series of VRS test flights. Would be an interesting paper for a aeronautical engineering student.
As soon as the pilot feels the low frequency airframe vibration and the trust variation, he/she should take action. The these indications must not necessarily come from VRS. It might be just the loss of ETL and some SWP. In which case VT would not save the day.
A down draft in the lee of a mountain isn't VRS, but it might feel quite similar.
To show different techniques to students is a great thing and letting develop a high sink rate and getting out of it, is something every student should know, but I believe that this is more a demonstration of the awkward aerodynamics of the helicopter than something useful in everyday life.
"All those terrible accidents" that FICH stated, do not happen. They are rather few and far between. VRS accidents are not on "most wanted" list of aviation authorities in the world. That's probably just because the training works pretty well to avoid the shaded area in the first place. When you have to use the Vulcan Technique to get you out of a desperate situation, you have already pretty much ****** it up before.
One thing might speak in favour of the Vulcan Technique. The two accident reports I found which suspect VRS stated that the pilot tried to arrest the sink rate by adding power; the natural reaction but makes it worse. A bit of uncoordinated flight or only stick forward might have saved the day here. Apparently the pilots didn't realise that they were in VRS.
The conclusion would be: show the students the Vulcan, but hammer it into their brain, to avoid VRS and if they get low frequency vibration and thrust variations, don't try to salvage an approach by just adding power and flying uncoordinated. Start again. Go around. Speed up. It might have been something else than VRS. It is easy to identify something when you want it to happen. It is much harder, if it surprises you.
It is an additional tool for the (advanced) pilot, but it is not the ultimate thing one would use in panic mode and it isn't universal. In a French of Russian helicopter you must reverse the movements. That just does not work for a standard emergency technique. Keep it stupid and simple.
Avoid imitations
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As I've written before, the maths don't justify the claims.
VRS can result in descent rates of 3,000 ft per minute or considerably more. Been there, seen it in a military Puma. VSI only went down as far as 2,500 fpm and it was firmly pegged on the bottom stop.
3,000 feet/min ROD = 34 mph downwards.
Some here claim that this can be stopped in less than 50 feet?
The claim is that aerodynamic control during the recovery from fully developed VRS is more effective and more sudden than an emergency stop in a car on a dry road! Try driving any non-ABS equipped car at 34 mph, applying maximum braking and see how long the skid marks are.
VRS can result in descent rates of 3,000 ft per minute or considerably more. Been there, seen it in a military Puma. VSI only went down as far as 2,500 fpm and it was firmly pegged on the bottom stop.
3,000 feet/min ROD = 34 mph downwards.
Some here claim that this can be stopped in less than 50 feet?
The claim is that aerodynamic control during the recovery from fully developed VRS is more effective and more sudden than an emergency stop in a car on a dry road! Try driving any non-ABS equipped car at 34 mph, applying maximum braking and see how long the skid marks are.
Oh no, 20 to 30 feet.
But let's assume they had 1500ft/min ROD which is more realistic in the R22 and that would be just 17mph.
That is a mere 3.17m/s^2
Possible. It is a third of one g. Around 19deg of bank? Not something that folds the blades.
But that is with instruments that lag and the human eye. It would be interesting to use one of flight recorders for sail planes to get a more accurate reading.
With your numbers it would be 7.62m/s^2 and it would take about two seconds, until the descend stops. Not unheard of.
But let's assume they had 1500ft/min ROD which is more realistic in the R22 and that would be just 17mph.
That is a mere 3.17m/s^2
Possible. It is a third of one g. Around 19deg of bank? Not something that folds the blades.
But that is with instruments that lag and the human eye. It would be interesting to use one of flight recorders for sail planes to get a more accurate reading.
With your numbers it would be 7.62m/s^2 and it would take about two seconds, until the descend stops. Not unheard of.
Last edited by Rotorbee; 18th Feb 2016 at 14:10. Reason: New numbers.
Avoid imitations
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.....let's assume they had 1500ft/min ROD which is more realistic in the R22
Which is exactly my point and is shown by the diagram above. It looks similar for the JetRanger.
Ray Prouty writes:
and
Which again is confirmed in the diagram.
I do not know the down wash velocity of the Puma, but it is possible that at 3000ft/min the ship is already in the powered autorotative state. Which must feel quite similar to IVRS, since a portion of the downwash is still pushing against the upflow and therefore inducing vibrations, but the vortex around the blade is gone.
And from Dr. J. Gordon Leishman. “Principles of Helicopter Aerodynamics, 2nd Edition – Helicopter Performance”
I think we are all guilty of a misconception. FDVRS in helicopter aerodynamics is NOT defined by THE HIGHEST SINK RATE but by the worst turbulence and thrust variation (and the existence of the vortex obviously).
@TC: The Vulcans have given us Pok Tar.
Ray Prouty writes:
“In a wind tunnel or long track test, the instability can be documented because the model can’t go anywhere. In flight, however, the instability prevents the pilot from finding a steady flight condition in which to take data. The flight test points in the literature that are identified as being taken in the vortex ring state were undoubtedly obtained under highly transient conditions.”
“Staying in the vortex ring for any length of time isn’t easy. It depends upon maintaining a nearly vertical flight path. There is some evidence, however, that a “glide” slope of about 70° is worse than a true 90° descent.”
I do not know the down wash velocity of the Puma, but it is possible that at 3000ft/min the ship is already in the powered autorotative state. Which must feel quite similar to IVRS, since a portion of the downwash is still pushing against the upflow and therefore inducing vibrations, but the vortex around the blade is gone.
And from Dr. J. Gordon Leishman. “Principles of Helicopter Aerodynamics, 2nd Edition – Helicopter Performance”
· While operation in the VRS is obviously undesirable, it can be entered inadvertently through poor piloting technique. Recovery is usually attained quickly, however, by the application of cyclic control inputs to cause some increase in forward or sideward airspeed to sweep the recirculating wake away from the rotor disk.
@TC: The Vulcans have given us Pok Tar.
Last edited by Rotorbee; 18th Feb 2016 at 18:00. Reason: Even more aerodynamics
For example, i fly the helicopter into vrs. Random yaw, vibrations etc. I don't do anything. Sinkrate begins to increase. I don't do anything. At 1000ft/min, i apply power. Sinkrate increases more. Is that IVRS or full developed VRS?
Only that we speak about the same..
Only that we speak about the same..
And in this full developed VRS we practice the recovery with our students and pilots. And it needs very little height!
Have you ever tried it?
Have you ever tried it?
Found a neat little video about the Cabri in VRS:
Note how long it takes to get the ship sinking and then it peeks at about 1000ft/min ROD. That's a gentle little beast.
Note how long it takes to get the ship sinking and then it peeks at about 1000ft/min ROD. That's a gentle little beast.
TC, I know you are pretty good at what you do, but give Prouty and other aerodynamist credit for their work.
If Vd/vi (thats decent velocity over induced velocity) is above 1.5, they at least consider the vortex gone for good. That's about 2000ft/min in anything I know.
If I say VRS, I mean both, IVRS and FDVRS.
I at least learned something about it during the course of this discussion.
a. Normal recovery or DT is frankly a moot discussion. If I get into really bad shacking and waggling I have messed it up so profoundly in the beginning, that 30 or 50 feet do not make a big difference.
b. From reading a few things, dusting of Prouty's books, and yes, quite a bit googling, I learned that The Beast is elsewhere, not in the descend rate.
And if Dr. Gordon Leishman's book wasn't so expensive, It would be on the way to my desk by now (if anybody has a copy he does not need anymore? And there is an article about VRS in the AHS Journal, could somebody scan that for me, please with a cherry on top?). But now I know, I can much safer descend straight down, than in a 40° angle and suddenly the Super Puma accident makes sense and a lot more does, too. It think, I am at least on the right track to understand VRS a bit better. I was taught in beginning things that are not true. I truly believed in gyroscopic precession (and I looked at a rotor head and the angle wasn't 90°. That's were I started to get suspicious), in the centrifugal force, density altitude affects turbine engines. You can count down almost all the myths Nick brought up in that famous thread, I would probably been a believer at one time in my life.
If anybody wants to believe the FDVRS with high sink rate, be my guest. You can try to explain to me the VRS diagram above with the high sink rate, I am all game and I will not interrupt and I will admit that I am wrong and I can't read the diagram correctly, but in that case, you might contradict a few giants in helicopter aerodynamics, behind which I hide.
If Vd/vi (thats decent velocity over induced velocity) is above 1.5, they at least consider the vortex gone for good. That's about 2000ft/min in anything I know.
If I say VRS, I mean both, IVRS and FDVRS.
I at least learned something about it during the course of this discussion.
a. Normal recovery or DT is frankly a moot discussion. If I get into really bad shacking and waggling I have messed it up so profoundly in the beginning, that 30 or 50 feet do not make a big difference.
b. From reading a few things, dusting of Prouty's books, and yes, quite a bit googling, I learned that The Beast is elsewhere, not in the descend rate.
“Much of our knowledge of this state comes from flight and wind tunnel tests. Based on this experience, we know that unsteadiness starts at about one-quarter, peaks at three-quarters, and disappears at 1¼ times the hover induced velocity.”
Raymond W. Prouty. “Helicopter Aerodynamics – Vertical Climbs and Descents”
Raymond W. Prouty. “Helicopter Aerodynamics – Vertical Climbs and Descents”
If anybody wants to believe the FDVRS with high sink rate, be my guest. You can try to explain to me the VRS diagram above with the high sink rate, I am all game and I will not interrupt and I will admit that I am wrong and I can't read the diagram correctly, but in that case, you might contradict a few giants in helicopter aerodynamics, behind which I hide.
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.....let's assume they had 1500ft/min ROD which is more realistic in the R22
A lot of people will have a sink rate of 500-1,000 ft/min and some vibration and say they're in FDVRS, but I think they just have enough of the disc sticking out into the airstream that they're getting some net lift to keep the sink rate low. It's *hard* to find the center of the downwash and stay in it (unless it's snowing!).
In that R22 demonstration the transition from OGE hover to falling out of the sky gave little warning: I usually describe it to my students that it was like "stepping off a roof". Lots of fun, when you're at a few thousand feet!
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So what height, speed and rate of descent did you start this from?
Did you try it with left cyclic and right pedal (which would have given you more power available)?
Did you try it with left cyclic and right pedal (which would have given you more power available)?
Honestly this wasn't fully developed VRS. I was with a fairly inexperienced instructor, who'd just been shown this himself. To get anywhere close to the "real thing" I'd want to be with someone who has been there themselves, preferably several times.
We were at 1000 feet and let things develop for maybe one second before starting the recovery, so still very much incipient. We only did it with right cyclic / left pedal.
I'm sure it would be lots of fun to be a helicopter test pilot - but I'm not one!