When practicing vortex ring.........
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So tempting to make a cheap remark about clouds and heads being in them. But I won't
Last edited by before landing check list; 3rd Jul 2012 at 05:52.
So this tedious, self-justifying post is your idea of humility is it? Good grief.
To my mind, you are making this much too complicated. Of course you can use the airspeed indicator. It can be used to bleed off of airspeed until in a range where indications are unreliable. Beyond this the pilot will sense the aircraft losing translational lift. The airspeed indicator is used during recovery precisely because any clear indication of airspeed shows that the aircraft has flown clear of its own vortices and collective can be applied again without the risk of falling through the floor.
To my mind, you are making this much too complicated. Of course you can use the airspeed indicator. It can be used to bleed off of airspeed until in a range where indications are unreliable. Beyond this the pilot will sense the aircraft losing translational lift. The airspeed indicator is used during recovery precisely because any clear indication of airspeed shows that the aircraft has flown clear of its own vortices and collective can be applied again without the risk of falling through the floor.
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So this tedious, self-justifying post is your idea of humility is it? Good grief.
Last edited by before landing check list; 3rd Jul 2012 at 06:46.
Shawn
Your post is spot on for a 300, having said that I find you need more than 500fpm rate of descent. The buffeting you talk about I think of as a loss of translatinonal lift, the pitching rolling can be the student not getting the ac into a slow speed much like hover taxying down wind. ( assumption we are flying downwind)
At a 500 fpm rate of descent the 300 will power out of the descent by using collective. This tells me that the ac has not " caught up" its own downwash. To actually achieve the symptoms of vortex ring I find you need more like 800 fpm at which point things do become more interesting.
Personally I think this subject ( lesson 15) is very badly taught in this country with instructors not really being shown waht it is
Your post is spot on for a 300, having said that I find you need more than 500fpm rate of descent. The buffeting you talk about I think of as a loss of translatinonal lift, the pitching rolling can be the student not getting the ac into a slow speed much like hover taxying down wind. ( assumption we are flying downwind)
At a 500 fpm rate of descent the 300 will power out of the descent by using collective. This tells me that the ac has not " caught up" its own downwash. To actually achieve the symptoms of vortex ring I find you need more like 800 fpm at which point things do become more interesting.
Personally I think this subject ( lesson 15) is very badly taught in this country with instructors not really being shown waht it is
Avoid imitations
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I was first shown VR in a Whirlwind 10, as part of the RAF's basic rotary course.
This was on the same sortie as the retreating blade stall demo (which I'd in fact already seen, courtesy of my instructor who got to Vne running in for a quickstop then pulled too hard in a turn, at about 150 feet agl. Thankfully, the turn was a right handed one, so the Whirlybird flicked upright, rather than inverted, or I might not be here today.
Anyway, VR! We were required to climb to 10,000 feet and wear parachutes for this instructional sortie. My QHI must have chickened out at the incipient stage because I don't remember anything particularly exciting happening. He wouldn't do the demo again!
Next time I saw VR was about twelve years later in a Puma HC1, during a night operational sortie. We were doing a certain job where we were required to hover as high as we could to avoid detection from "unfriendlies" on the ground. Gaining the hover (more or less on instruments) involved flying a slightly climbing, into-wind quickstop (we found that we made less blade slap that way) at around 10,000 feet. If the aircraft fell out of the hover attempt due to lack of power, we were too high for the ambient conditions so we would fly a racetrack, flying forwards and down by a thousand feet or so, then try again. When we subsequently achieved a hover, we then checked max continuous engine power wasn't being exceeded (normally the limit was N1s, the Turmos ran quite cool). If it was, again we move fly forwards and down until we were in limits. If we had some spare power, and our own folks on the ground advised they could hear us, we would pull to the N1 limit and climb vertically until the aircraft settled at it's preferred altitude.
I was acting as co-pilot on this occasion and we had been flying for about four or five hours, so we were getting tired (we wore NVGs, too, which didn't help).
One of my ex-students from some years before was flying the aircraft and operating as captain. There was little or no wind (we would obviously try and find the wind if possible, to make the job easier and to get higher). We had a "cross hairs hovermeter" but as it was Doppler based it often was inaccurate at the altitudes we operated at.
As the aircraft partly "settled" in the first attempt at a free air hover, I felt through the seat of my pants that we were beginning to move backwards slightly, although we had no visual references. The aircraft then suddenly pitched slightly nose up (I think this was the rearwards airflow hitting the top of the stabiliser).
Suddenly, the instruments came alive. Unfortunately, not the ASI, but the altimeter began rapidly unwinding and the VSI needle went very rapidly to the bottom stop (2500 FPM plus). The aircraft then exhibited classic signs of VR, randomly pitching, rolling and yawing. I called "Airspeed!" twice, no apparent recovery action was taken. I then called it a third time, and gave a very strong hint by pushing forwards on the cyclic with the palm of my hand. The handling pilot then woke up to what was required and as the ASI was showing some action, he recovered as for an IMC "U.P."
We lost a lot more than 3,000 feet, in a very short time. The debrief was short as we were very tired after flying all night.
This was on the same sortie as the retreating blade stall demo (which I'd in fact already seen, courtesy of my instructor who got to Vne running in for a quickstop then pulled too hard in a turn, at about 150 feet agl. Thankfully, the turn was a right handed one, so the Whirlybird flicked upright, rather than inverted, or I might not be here today.
Anyway, VR! We were required to climb to 10,000 feet and wear parachutes for this instructional sortie. My QHI must have chickened out at the incipient stage because I don't remember anything particularly exciting happening. He wouldn't do the demo again!
Next time I saw VR was about twelve years later in a Puma HC1, during a night operational sortie. We were doing a certain job where we were required to hover as high as we could to avoid detection from "unfriendlies" on the ground. Gaining the hover (more or less on instruments) involved flying a slightly climbing, into-wind quickstop (we found that we made less blade slap that way) at around 10,000 feet. If the aircraft fell out of the hover attempt due to lack of power, we were too high for the ambient conditions so we would fly a racetrack, flying forwards and down by a thousand feet or so, then try again. When we subsequently achieved a hover, we then checked max continuous engine power wasn't being exceeded (normally the limit was N1s, the Turmos ran quite cool). If it was, again we move fly forwards and down until we were in limits. If we had some spare power, and our own folks on the ground advised they could hear us, we would pull to the N1 limit and climb vertically until the aircraft settled at it's preferred altitude.
I was acting as co-pilot on this occasion and we had been flying for about four or five hours, so we were getting tired (we wore NVGs, too, which didn't help).
One of my ex-students from some years before was flying the aircraft and operating as captain. There was little or no wind (we would obviously try and find the wind if possible, to make the job easier and to get higher). We had a "cross hairs hovermeter" but as it was Doppler based it often was inaccurate at the altitudes we operated at.
As the aircraft partly "settled" in the first attempt at a free air hover, I felt through the seat of my pants that we were beginning to move backwards slightly, although we had no visual references. The aircraft then suddenly pitched slightly nose up (I think this was the rearwards airflow hitting the top of the stabiliser).
Suddenly, the instruments came alive. Unfortunately, not the ASI, but the altimeter began rapidly unwinding and the VSI needle went very rapidly to the bottom stop (2500 FPM plus). The aircraft then exhibited classic signs of VR, randomly pitching, rolling and yawing. I called "Airspeed!" twice, no apparent recovery action was taken. I then called it a third time, and gave a very strong hint by pushing forwards on the cyclic with the palm of my hand. The handling pilot then woke up to what was required and as the ASI was showing some action, he recovered as for an IMC "U.P."
We lost a lot more than 3,000 feet, in a very short time. The debrief was short as we were very tired after flying all night.
10,000 feet AGL? No wonder the Instructor chickened out! :roll eyes:
That violates the "Single Breath Scream Rule" by a bunch!
That violates the "Single Breath Scream Rule" by a bunch!
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Interestingly in the book "Dynamics of Helicopter flight" By G Saunders, there is a graph which shows, presumably as a result of tunnel investigation, that the most severe symptoms of VR occur when the helicopter is descending at angles between approximately 80 and 40 degrees to the vertical, not in true vertical descent relative to the air but without any explanation of why. He quotes a reference to J Wolkovitch and R P Walton, "Stability and Control of Helicopters in Steep Approaches. USAAVLABS Technical Report 70-74A.
Last edited by rotorfossil; 3rd Jul 2012 at 15:06.
Wind tunnel tests also show that your RoD has to be at least half of your downwash speed, preferably in excess of 0.6.
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One of my past instructors(exRAF) who whilst on my check flight was quizing me on what I would do if I entered VR or SWP, my answer was the right one, but then he suggested he show me just what happens so I would understand more about it and always be aware of just how fast things happen when getting into that state, we ascended to about 2500 ft and purposely guided by him I entered into the realms of VR we needed, he talked me into the start of the problem and then pointed out the rate of descent, it was approaching 2000ft per min, he asked me to get out of it to see if my mind set could convert the problem into a safe area of flight, as you can see I am still here and really grateful for that positive lesson, even though in my original lessons the FTI had showed me this it was nothing like the thing my check pilot showed to me,.. the ease in which the VR state can be got into was a real jolt to my knowledge but equally if you have height you can always recover, providing you can dip ut and gain speed.
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nice vortices
Last edited by AnFI; 7th Jul 2012 at 00:18.
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Mention of Crab's name this am reminded me of some unfinished businees in this thread, so here goes.
Plenty of ways or “situations” to get into VRS as we see by reading this thread and ‘visualizing the old balloon’ trick simplifies things. The easiest way is to hover in formation with an imaginary balloon. Forget about ground wind speed or direction, just stay in station laterally and then descend in a SWP mode into your own downwash at a rate to induce recirculation, bingo.
In effect your whole machine complete with its recirculating vortices as separate from the surrounding air mass is inside the balloon, in freefall, falls quick eh? Then all of a sudden the balloons skin cannot hold on any more and away it blows. Whoosh, the aircraft goes straight into Crab’s definition of windmill effect. Simple, that’s the sequence of ab initio training for VRS that I do. I may do that three or four times in the one exercise starting from say 2,000 feet. Other low level exercises complete the picture.
In that scenario you simply cannot fall thousands of feet, I have done it hundreds of times in R22, R44’s and B47’s. In each of those the freefall ‘bit’ accounts for no more than 120 feet or a bit more, that is the A/C is either balanced and or steered so that it remains level within the vortices and won’t automatically tip toward a C of G displaced from the C of L to take it out into fresh air during that ‘bit’.
At the point where the whoosh occurs is the one place that I worry about relative A of A and whether it may be enough to stall the rotor blade. R22 rotor blades stalled are not a pretty sight, we all know that. Perhaps as the power is still on with N/R top of green, allows them to resist any bending and maybe they do stall momentarily, I don’t know.
I do know there is no mention of limitation for the manoeuvre in any of those POHs, so the test pilots and gurus must have considered and accepted the procedure.
Let me turn to the statement “deep VRS”. This confuses me and may be something that confuses less experienced people if not is frightening as a phobia. As I explained above it is to me a furphy. Do some aircraft develop another flight characteristic that is frightening and thus would be dangerous from a low level entry through SWP into VRS? Let’s look.
The lift for most helicopters occur on the outer ends of the blade / disc not in at the roots of the blades, in fact various sections of the blades are driving or driven in normal flight and in the hover. One only needs to damage a small portion of blade tape on the outer end to see how much lift is lost and therefore how much lift occurs at the outer ends of the blade.
It is simply impossible for circulating vortices to remain attached to the disc in the face of say a 6,000fpm descent or more of directly opposing airflow. What I suspect happens in the case where aircraft that have entered as in a classic SWP thru to VRS manoeuvre and then fall for up to 12,000 feet or more have stalled the rotor blade tips.
A stalled airfoil always needs airflow to come from a different direction to displace the stall, which of course is an attached vortices that destroy lift and is on the upper side of the blade /airfoil out of the upcoming and relative airflow.
In VRS the blades / disc are always steerable, to wit the recovery, cyclic is moved forward or any which way, therefore they are not stalled. Stalled blades won’t be steerable.
This is a common phenomenon in various types of fixed wings; they get stalled, deep stalled where the tail plane is also stalled and the pilot can’t get out of the stall, because he can’t change the direction of the stalled airfoils. He must then either jump out or crash with it.
Perhaps a quickly developed blade stall not VRS, is what happens with the Sycamore type for example I think was mentioned, tapered blades rigid enough to resist bending but the pesky things are carrying their stalled condition for a long time, up to twelve thousand feet in fact and at a very high rate of descent, some of the accounts are. Sure as god make little green apples they won’t be carrying recirculating vortices will they?
That to me is not a condition of “DEEP VRS” it is a situation of stalled airfoil. Perhaps this deep VRS is nothing but a long held misconception covering a much more dangerous flight characteristic.
Of course anyone can go out with smoke generators and prove me wrong; it would be easy to see. Someone else can do it in those nasty drop-a-lot turnouts though.
VRS is a condition which must be learnt, it is possibly the major cause leading to the overpitched condition which claims most low level accidents. Pilots whistle around the corner all of a sudden fall out of the sky, get a fright and pull too much pitch instead of recovering, N/R and engine RPM and power decays, blades stall, A/C falls, end of story.
It’s easy enough to get into and with education for quick recovery you should never fall more than 80 feet in a light machine; remember if entry is at 50’ only the last 30’ hurt.
It is also easy enough to whistle around the corner chasing belligerent cattle and dammit straight into overpitch, those not trained to recover properly crash (happening regularly lately). Those better trained recover – and with more training again, they recover - and - manage to keep control of the belligerents. A good point is that nowadays we have lots less in the way of belligerence in the cattle, in itself a trap for when it suddenly looms and has to be controlled. “Situations” may develop that haven’t been seen.
Or people stuff up a simple quick stop, overpitch and crash, one of those at the Finke Desert Race recently.
As CAGS points out the other low level malady although much less likely with mustering pilots is the simple settling with power. He will surely remember the infamous Sydney city to surf B206 accident of quite some years ago where a fully serviceable machine was flown into the ground at a steady rate of descent = power settling.
VRS = dramatically fast ROD, is not a death dealing phobia, shooting the tube I call it, learn it and live.
My point of view is that when we do intentional training we first set up a SWP situation which is a slower but controlled descent rate, then increase descent rate until the tip vortices begin recirculating where we lose control of the descent rate and the aircraft thus enters VRS and falls – with those clinging vortices until they are either blown away by the fast resultant airflow or we tip the aircraft over so that it enters new clean air of its own accord and thus leaves the vortices behind.
Here this time we have not talked about another quick way of recovery from the very early onset of VRS, aircraft first sensed as sinking – quick flick up of collective to defeat the recirculating vortices – but be aware that immediately that may put you in an over pitched situation and you need to get the collective down sharply to recover that condition.
One thing I find disturbing and Shytorque has described it well, is that many students – now experienced pilots - have not developed that sense of preservation of being in control of the aircraft instead of the other way around, and will not show awareness of, or are sensing quickly enough the initial stage of the falling of it and the recovery necessary. Whether it is because they are not prepped into this chain of logical thought as students or not, I don’t know. But the correct circuitry of thinking – if I can put it like that - must be able to be brought up at random, because it can grab you at any time, real easy.
Crab, are you happy with those thoughts, have you done any in a R22? If not can you have a go at going up and developing this “DEEP VRS” thingy and let us know how you go because I am buggered if I can?
Plenty of ways or “situations” to get into VRS as we see by reading this thread and ‘visualizing the old balloon’ trick simplifies things. The easiest way is to hover in formation with an imaginary balloon. Forget about ground wind speed or direction, just stay in station laterally and then descend in a SWP mode into your own downwash at a rate to induce recirculation, bingo.
In effect your whole machine complete with its recirculating vortices as separate from the surrounding air mass is inside the balloon, in freefall, falls quick eh? Then all of a sudden the balloons skin cannot hold on any more and away it blows. Whoosh, the aircraft goes straight into Crab’s definition of windmill effect. Simple, that’s the sequence of ab initio training for VRS that I do. I may do that three or four times in the one exercise starting from say 2,000 feet. Other low level exercises complete the picture.
In that scenario you simply cannot fall thousands of feet, I have done it hundreds of times in R22, R44’s and B47’s. In each of those the freefall ‘bit’ accounts for no more than 120 feet or a bit more, that is the A/C is either balanced and or steered so that it remains level within the vortices and won’t automatically tip toward a C of G displaced from the C of L to take it out into fresh air during that ‘bit’.
At the point where the whoosh occurs is the one place that I worry about relative A of A and whether it may be enough to stall the rotor blade. R22 rotor blades stalled are not a pretty sight, we all know that. Perhaps as the power is still on with N/R top of green, allows them to resist any bending and maybe they do stall momentarily, I don’t know.
I do know there is no mention of limitation for the manoeuvre in any of those POHs, so the test pilots and gurus must have considered and accepted the procedure.
Let me turn to the statement “deep VRS”. This confuses me and may be something that confuses less experienced people if not is frightening as a phobia. As I explained above it is to me a furphy. Do some aircraft develop another flight characteristic that is frightening and thus would be dangerous from a low level entry through SWP into VRS? Let’s look.
The lift for most helicopters occur on the outer ends of the blade / disc not in at the roots of the blades, in fact various sections of the blades are driving or driven in normal flight and in the hover. One only needs to damage a small portion of blade tape on the outer end to see how much lift is lost and therefore how much lift occurs at the outer ends of the blade.
It is simply impossible for circulating vortices to remain attached to the disc in the face of say a 6,000fpm descent or more of directly opposing airflow. What I suspect happens in the case where aircraft that have entered as in a classic SWP thru to VRS manoeuvre and then fall for up to 12,000 feet or more have stalled the rotor blade tips.
A stalled airfoil always needs airflow to come from a different direction to displace the stall, which of course is an attached vortices that destroy lift and is on the upper side of the blade /airfoil out of the upcoming and relative airflow.
In VRS the blades / disc are always steerable, to wit the recovery, cyclic is moved forward or any which way, therefore they are not stalled. Stalled blades won’t be steerable.
This is a common phenomenon in various types of fixed wings; they get stalled, deep stalled where the tail plane is also stalled and the pilot can’t get out of the stall, because he can’t change the direction of the stalled airfoils. He must then either jump out or crash with it.
Perhaps a quickly developed blade stall not VRS, is what happens with the Sycamore type for example I think was mentioned, tapered blades rigid enough to resist bending but the pesky things are carrying their stalled condition for a long time, up to twelve thousand feet in fact and at a very high rate of descent, some of the accounts are. Sure as god make little green apples they won’t be carrying recirculating vortices will they?
That to me is not a condition of “DEEP VRS” it is a situation of stalled airfoil. Perhaps this deep VRS is nothing but a long held misconception covering a much more dangerous flight characteristic.
Of course anyone can go out with smoke generators and prove me wrong; it would be easy to see. Someone else can do it in those nasty drop-a-lot turnouts though.
VRS is a condition which must be learnt, it is possibly the major cause leading to the overpitched condition which claims most low level accidents. Pilots whistle around the corner all of a sudden fall out of the sky, get a fright and pull too much pitch instead of recovering, N/R and engine RPM and power decays, blades stall, A/C falls, end of story.
It’s easy enough to get into and with education for quick recovery you should never fall more than 80 feet in a light machine; remember if entry is at 50’ only the last 30’ hurt.
It is also easy enough to whistle around the corner chasing belligerent cattle and dammit straight into overpitch, those not trained to recover properly crash (happening regularly lately). Those better trained recover – and with more training again, they recover - and - manage to keep control of the belligerents. A good point is that nowadays we have lots less in the way of belligerence in the cattle, in itself a trap for when it suddenly looms and has to be controlled. “Situations” may develop that haven’t been seen.
Or people stuff up a simple quick stop, overpitch and crash, one of those at the Finke Desert Race recently.
As CAGS points out the other low level malady although much less likely with mustering pilots is the simple settling with power. He will surely remember the infamous Sydney city to surf B206 accident of quite some years ago where a fully serviceable machine was flown into the ground at a steady rate of descent = power settling.
VRS = dramatically fast ROD, is not a death dealing phobia, shooting the tube I call it, learn it and live.
My point of view is that when we do intentional training we first set up a SWP situation which is a slower but controlled descent rate, then increase descent rate until the tip vortices begin recirculating where we lose control of the descent rate and the aircraft thus enters VRS and falls – with those clinging vortices until they are either blown away by the fast resultant airflow or we tip the aircraft over so that it enters new clean air of its own accord and thus leaves the vortices behind.
Here this time we have not talked about another quick way of recovery from the very early onset of VRS, aircraft first sensed as sinking – quick flick up of collective to defeat the recirculating vortices – but be aware that immediately that may put you in an over pitched situation and you need to get the collective down sharply to recover that condition.
One thing I find disturbing and Shytorque has described it well, is that many students – now experienced pilots - have not developed that sense of preservation of being in control of the aircraft instead of the other way around, and will not show awareness of, or are sensing quickly enough the initial stage of the falling of it and the recovery necessary. Whether it is because they are not prepped into this chain of logical thought as students or not, I don’t know. But the correct circuitry of thinking – if I can put it like that - must be able to be brought up at random, because it can grab you at any time, real easy.
Crab, are you happy with those thoughts, have you done any in a R22? If not can you have a go at going up and developing this “DEEP VRS” thingy and let us know how you go because I am buggered if I can?
Last edited by topendtorque; 18th Jul 2012 at 23:36.
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In VRS the outboard section of blade is producing little lift due to ingestion of tip vortices reducing the angle of attack. Inboard section is producing little lift due to reaching stalling angle of attack. Middle section of blade is struggling to provide lift. Pulling more pitch exacerbates the situation.
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Back in '66 I was taken up in a Wasp by an ETPS graduate and at 9000ft he demonstrated fully developed vortex ring. If I recall correctly we dropped nearly 5000ft before we were fully out of it 
. It absolutely petrified me at the time but was a good lesson although I wouldn't have wanted to experience it again.
. It absolutely petrified me at the time but was a good lesson although I wouldn't have wanted to experience it again.
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I recently heard about such a 'demo' exercised by a very(!) experienced EC pilot many years ago in a BO105. Motto: Let me show you how this works.
Demo started with a clearance at 13.000' near Ottobrunn and ended .... at 2.800' ... the two POB did only survive because they both leaned forward as the aircraft had a complete loss of control ... pitch was through the floor (literally) and PF was definately not PIC anymore.
From my point of view for some things in life it is absolutely ok to know what can happen, to realise the beginning stage and the action you have to take not to really get into trouble.
Demo started with a clearance at 13.000' near Ottobrunn and ended .... at 2.800' ... the two POB did only survive because they both leaned forward as the aircraft had a complete loss of control ... pitch was through the floor (literally) and PF was definately not PIC anymore.
From my point of view for some things in life it is absolutely ok to know what can happen, to realise the beginning stage and the action you have to take not to really get into trouble.
