vortex ring alt + vsi

[levo]

Just a little question
When in vortex ring state will the VSI and Altimiter read or show the helicopter is desending

Many thanks Levo.

[Outwest]

Will they ever!!! Those hands on the altimeter will be a blurr, but you won't notice because you will be too busy Sh$%$ing your pants:eek:

[Um... lifting...]

Yes. Can't think of any reason why it shouldn't.
Static pressure entering the static ports isn't affected in vrs (vrs is related to air velocity through the rotor system, not static pressure), and depending upon the design of the VSI or IVSI, it will either just take static pressure change or will have an accelerometer incorporated to speed up the readings.
Outwest, remind me never to give you the controls...:uhoh:

[Outwest]

Until you've been in VRS, no further comment required

[NickLappos]

Any screwball condition will alter the absolute accuracy of the static system, especially if the static ports see any head-on air impacts, but the high rate of descent of VRS is quite enough to be sure that you see a big indicated descent rate while in VRS.

BTW, lets uncan the great debate: VRS occurs at quite a bit more than 300 fpm, it must be about 3/4 of the rotor downwash velocity where the downwash cannot get out of the way of the descending rotor. This is always a much higher rate of descnet than 300 fpm.

Why do instructors say otherwise, and demonstrate "VRS" in slight descents that seem to "prove" otherwise? Because there is an increase in power required at 300 fpm, which can fuel a vast over-pitching that turns into VRS if left unattended. The typical VRS demonstration is actually a demo of increased ROD due to the unstable nature of a hover descent - where some ROD makes the power needed to hover rise a slight amount. When the instructor forbids any collective rise, the descent increases (not yet VRS, just a hairy increasing vertical descent) until real VRS can be experienced (at 3/4 of the downwash speed). The aerodynamics of VRS assure that it CANNOT be experienced unless the aircraft is at or near zero forward velocity and at or near the downwash velocity - somewhere above 750 ppm for a light helo, and near 1500 fpm for a big one.

[Um... lifting...]

The stock numbers I've always read and was taught were IAS < 40 (and in some machines, like the B206, IAS is unreliable below 40), VSI > -800fpm. I suspect that those numbers don't get one INTO VRS, but reduce the margin of safety to the point that it's a lot easier to get into VRS from that point. Nick, of course you're correct that there will be a loss of precision in static system, but even ignoring your stomach in your throat I think it will still be fairly apparent from the instruments that the machine's entering a pretty hefty rate of descent.
My experience is that interaction with such things as cliffs, ship's smokestacks and stack gas and/or other obstructions can change downwash patterns to such an extent that loss of lift can occur startlingly quickly. Whether any of that is actually VRS is probably not too important, but what is important is to predetermine how you're going to get out of it should you find yourself in it.
Outwest... a fellow I once flew with got into VRS once and tried to get into it a second time in one day while trying to descend to a SAR target with a substantial tailwind. I got us out both times precisely because he was rushing himself, target fixating and busily doing what you recommend rather than fly the machine... I would say my response was perhaps more appropriate. Ball's in your court, mate.

[hihover]

May I be so bold as to offer a few of my thoughts on VRS:

1. Levo - as already covered by Nick and Um... yes they will indicate a descent.

2. The descent rate will be high but the instruments will be readable unless you allow the situation to go uncorrected, it then becomes quite unpredictable.

3. Nick, I think the figure of 300fpm used by many instructors is, as Um... says, a sort of "alarm bell" figure, eg, I insist that during the approach, as the speed reduces through 30 kts, the rate of descent should be less than 300 fpm. Bearing in mind that this is being taught to student pilots who need bench-marks in the early days to keep them out of difficult situations.

As far as demonstrating VRS goes, what a silly idea. Just like arterial bleeding, I don't need to see it to be aware of how dangerous it is. The incipient VRS demonstrations given by instructors are aimed at showing the student how unpredictable the helicopter can be if power is applied when in a high rate of descent with low speed and how to recover from that situation by increasing speed. The demo should not be allowed to develop into anything near VRS but simply to serve as a severe warning that helicopters will bite your ar$e if you are not careful, therefore, when reducing speed through 30 kts...........etc etc.

Intentional VRS should be left to you test pilots if you feel the need.

[Outwest]

Someone needs to lighten up......now I remember why I stopped posting here.......and I ain't your mate.

[Um... lifting...]

Someone needs to lighten up......now I remember why I stopped posting here.......and I ain't your mate.

I agree... and I hope it works out that you do... as for me, I'm going surfing...
Also, you need to get out more... and get a better grip on colloquial English.
"Mate" isn't an expression that gives a lot of people offense...
I don't know why the original question was asked, but I assume unless it's clear otherwise that the original questioner asked it in earnest. I'm not sure your answer was a whole lot of use... so maybe it's best that you did stop posting... mate.

[Tourist]

Deliberate Vortex ring is part of the annual check in the Royal Navy, and I think it is a useful reminder.
You can tell people something is scary, but until they do it for themselves, it isn't quite the same.

[hihover]

A dear old guy called Lofty Marshall at CFS(H) discussed VRS with me and how they used to teach it years ago, until they started filling up skips with helicopters. Do bear in mind, recovering from incipient vortex ring is not a recovery from the real deal.

Like several other exercises (EOLs and Tail Rotor problems included), they may have value, but that value has to be balanced with the training risk and the likelyhood of the actual event.

The actual event of VRS can be avoided through correct handling and awareness.

Don't get me wrong, if you want an annual reminder of the dangers to be demonstrated to you and pusser pays for it then fill your boots. I prefer to discuss it and lay down parameters that will ensure its avoidance.

[nigelh]

:D quite agree....mate :ok: at the same time you could stop robbo,s practicing engine off,s into the deck too and we can all get an insurance rebate :ok::ok:
ps you cant get into vortex whatever speed or rate of descent without pulling power..

[topendtorque]

Just a little question
When in vortex ring state will the VSI and Altimiter read or show the helicopter is desending


Just a little answer as I do them repeatledy in C& T, just today again.

Firstly, your VSI will indicate almost immediately, then it willl slow right down as you quickly get out of it. That is how that instrument works.

Your Alt will not register the event until after it has happened. That is because that instrument always is slow to wake up. It will portray it fairly well when it does though.

For your info you can look up other threads that go into the detail, but it is impossible to retain any machine in VRS for a period of time longer than; OMG it's dropping like a stone, f@@# what was that.

Please do not enter VRS below eighty feet AGL, as that is about the usual drop in a light helicopter. (inadvertant or deliberate, all tied up in the physics you know, nudge nudge, wink wink)

Any factor the balance of eighty is the only factor that will EVER remain painful.

Any factor that balances nigelh will be an freudan expression in itself. He still hasn't worked out that nearly all EOT is done in ab initio training, in R22's. Poor boy!
Perhaps he should volunteer his squirrel for this type of work?

[Thomas coupling]

Sorry to have to correct you mate.....

One can only recover from incipient VRS. This is because the real m'coy does not enable the pilot to take control of the a/c. It is doing its own thing and will either terminate your flight violently or recover itself long enough for the pilot to do something about it. VRS is no longer demonstrated anywhere, to my knowledge for this very reason.
Having said that, does the american pilot interpret VRS as the UK IVRS???

[topendtorque]

Now Now thomas, long time no see, how are you doing.

one can definately recover incipient VRS.

One can definately put a machine into VRS and;

one can not hold it in because the upward rushing air will simply blow the recirculating air away. savvy??

all'a'same'as the limiting coefficient of static friction.

when one puts it into VRS, the relationship betwixt airframe and rotor disc can be safely maintained under full control to the highest integrity. fear not with an experienced person.
cheers tet

[hihover]

Thomas,

I'm with you on this one, recovery from VRS is practised at the incipient stage, because the real McCoy is too unpredictable and therefore, too risky.

Topend.... I'm not sure where your 80' figure comes from, I think we must be discussing different exercises.

Tam

[nigelh]

TOT mate...
English may be your second language ...so i shall explain s l o w l y ....
I know that eol,s are done mainly in training and therefore often in R 22,s....I am suggesting they stop doing them .....just as they have stopped demoing low g and now stopped demoing full swp..... as for using my squirrel ...i dont think you could afford it old boy :rolleyes:
ps check freudan spelling ....

[levo]

Just another little question

When a helicopter is in a quick stop and the blabes start to (bang slap)is this vrs for a moment until you level the helicopter .
If so would this be a early indication of VRS.
Or would there be any other indication apart from falling sensation


Thanks for your replys.

Levo.

[NickLappos]

The blade slap is BVI (Blade vortex Interference) and is not even a second cousin to VRS.

[levo]

Q to Nick Lappos.

Can this BVI damage the blades as it sounds awfull and is puting the machine under a lot of stress are there limits .

Thanks nick.

[levo]

Sorry to trouble you again Nick .

Is it posible you could elaborate more on BVI .

Once again Thanks.

Levo.

[Whirlygig]

as it sounds awfull

Not when SASLess did it in the Huey at Helitech last year!! :ok:You had to be there!!

Cheers

Whirls

[NickLappos]

levo,

Any wing produces a trailing vortex ("wake turbulance") due to the spillage that creates a neat little sideways tornado at the tips. The blade is of course a wing, and it produces a tip vortex. Because the whole flow field around the rotor is downward, this tip vortex descends as it leaves the blade tip.

The vortices can be seen when you hover over grass, they make the rapid beating of the grass that marks each blade passage.

In level flight, as the rotor turns, the next blade avoids the previous blades vortex because the downward drift of the vortex causes the miss. If the rotor is tilted back a bit, as in a quick stop, the "next" blade can hit the vortex and cause a bit of vibration and a slight "slap".

The most famous bit of Blade Vortex Interference (BVI) is the Huey "blade slap" in gentle descents at about 80 knots. Often the noise during translational roughness is BVI.

The blade stresses are not terrible during BVI, usually high speed flight and maneuvering are much harder on the blades.

Here is a blade tip vortex photo.

http://re3.mm-a4.yimg.com/image/2950965755


Here is a rotor blade shedding its vortex periodically:

http://www.fluid.tue.nl/GDY/acous/turbine/img/Schl.gif

Here is a NASA photo of one vortex path:

http://halfdome.arc.nasa.gov/research/images/shadow.gif

[levo]

Nick Lappos

Many thanks .

Levo.:ok:

[eagle 86]

Taught many years ago at a very respected School: conditions for entry into INCIPIENT VR - KIAS < 20, ROD > 200ft/min and a SIGNIFICANT increase in power. Watch VSI - I assure you you will see a rapid increase in ROD - hold these conditions and you WILL get into VR. What's happening? At the tip decreasing angle of attack (loss of lift) due re-ingestion of tip vortices, at the root increasing angle of attack to beyond stalling angle (more loss of lift), in the middle - an area of blade that is producing a diminishing amount of lift. Modern helos are less susceptable because of better blade design.
GAGS
E86

[[email protected]]

eagle - but I bet you didn't hold it - I bet you recovered as soon as the increase in RoD was apparent. That for TopendTorque is a demo of entry to and recovery from incipient VRS. It may well be what ToT is doing at 80' but it's not full VRS at all and frankly I wouldn't be doing an incipient demo at anything less than 2000' just in case.

[eagle 86]

Crab,
I think you and I probably trained at the same School - never said to hold it - but if you do then hang on it will be a ride and a half. Only last week I endorsed a chap on an A119 - among other tricks was IVR - I had 4,500 feet AGL!
GAGS,
E86

[topendtorque]

nigelh you are right, English is not my first tongue, low level rotary flight is, mainly of the ’47 dialect but more recently the last few k hours, I’ve included some robust superlatives to my vocabulary in the R22 inflection of the repartee’.

And no, I probably wouldn’t be able to afford the squirrel job; maybe I’ll try to put together a few gravel rashed pennies from the tougher chapters of my life as a down deposit. I am sure you recognise that I am not being derogatory with that, and I have already had a go at em, they don’t do much for me.

It may well be what ToT is doing at 80' but it's not full VRS at all

For Crab, no I don’t do fully blown VRS from eighty feet, heaven help us. We start the learning process from at least 2000’. Three reasons for that;

1) The instability of the T/R couple with the descent frightens the subject, they need frightening.

2) It takes all of that to get a macine (an R22 at least) to enter fully blown VRS maybe three times if you are lucky before finishing at 500’, and

3) There is plenty of time for the subject to observe the altimeter which will indicate just how long it was in VRS. This is usually no more than eighty feet, seen as a quick flick on the altimeter, after the event. The standard recovery usually does nothing more than flatten out the vertical descent long after VRS has departed.

It is important for the subject to understand that the most frightening thing about VRS is the incipient stage where the first symptom is that little sinking feeling in the pit of the stomach. This is not just another phenomenon that is occurring during the learning of this low level mystique and it’s OK if it happens because if it gets bad the C & T guy will take over!! Oh no, if you want to fail just think and act that.

This is why we play with the incipient stage, recognition and absolutely automatic recovery before it develops. Very important stuff for people who might have their attention diverted elsewhere, being shot at, cows running amok, targets turning downwind from gun or camera, fugitives trying to hide from the nite sun under brush when the wind is all over the joint, a camera man bellowing –this way that way, etc.

So as the subjects are being trained for an operational environment at below 100’ when their attention may be diverted elsewhere, then it follows to reason that I will first demonstrate at that height and less, the pitfalls, then over time try to trap them into ‘situations’ where they WILL get hurt if THEY don’t recover.

I wouldn't be doing an incipient demo at anything less than 2000' just in case.

As far as pussy footing around doing incipient VRS at above 2000’ Jesus Crab, get real, I had you pegged well above that sort of comment.
All it is is demonstration, awareness and covered practice, without getting tooo bogged down in theory.

It follows on from the downwind theory, you know, downwind, decreasing airspeed and descending are the same as drinking, driving and eventually death.
It’s the practical that counts, not some high falutin’ drummed up philosophy, which may well be dodgy.

I thoroughly applaud any institution that trains its subjects in the recognition and recovery from VRS, before it happens.
It will get you and it will hurt, which is why I use the statement –“notice that if you really stuff it up then you seldom fall more than eighty feet, so if you enter at fifty feet it is only ever the last thirty that will hurt”- end quote.

It usually gets the message across; my business is to protect people.

Can I go back to nigelh again, VRS and EOL’s and other known emergency exercises is all about the philosophies of circumstances that are a matter of chance not choice of our trade. I agree that Low G pushovers are absolutely stupid, and a manoeuvre of choice.

We once had a top dog check pilot from down south who (unbeknown to us) was demonstrating the low G pushover and then the recovery. This is until he came up against one youngster whom he frightened straight up and who said – “do that again an I’ll f’n choke yer”.

Exercise was finished, ops manager complained to, top dog smart a##e sent on next plane south and youngster well applauded.

We later heard that during the argument that youngster had said, ‘the reason I don’t wanner do it is because it’s in that book under yer f’n seat that it’s dangerous and I ain’t gunna do it, get it.’ Nuff said.

EOL’s are often a matter of chance not choice, just a couple of days ago a B206 went into the ocean off Queensland, the turbine spooled down I hear. How many threads here are started with the subject being an emergency landing, all sorts of aircraft?

And Nigel you are an old ’47 hand, if that is true, look me in the eye and tell me that you have never had an emergency auto. Of course you cannot. So we practice them, which is best done at the ab-initio stage and then usually it’s only needed for ‘differences of type’ later.

I have another saying- ‘practised dexterity in the areas of known emergencies will usually lead to automatic recovery in the areas of unknown emergencies.’ I have found that doctrine as cheap insurance. A salutary repast for all low level disciples.

I'm with you on this one, recovery from VRS is practised at the incipient stage, because the real McCoy is too unpredictable and therefore, too risky.

Hihover, you have thoroughly confused me, just what is dangerous about the manoeuvre, as long as it’s accomplished well away from the firmer terror?

Have ye never descended from a high rise in an express elevator? It's all the same, you descend in your own cocoon of air in ignorant bliss of the surroundings and at the bottom - you stop - the doors open - and - you step out into fresh air
No need for the canaries in your head to beat themselves into submission. You’ve obviously never practised the idea.

The blade stresses are not terrible during BVI, usually high speed flight and maneuvering are much harder on the blades.

I sincerely hope that this is the case as deliberate blade slap to project noise well ahead of you when moving mooies is a very much used tool. Of late we have heard it may contribute to pulling the skin off an R22 blade???

[hihover]

Topend -

You may wish to consider cutting the drama queen bullsh*t with your "subjects" being shot at and cows distracting their attention :yuk:, just for a few minutes, and consider what you are saying.

Flying a helicopter vertically downwards from 2000' and trying to force it to enter a state which is known to have caused accidents is risky, surely, through your macho, no poofters hardshell, even you must grasp that. No matter how good you are at doing it.

I don't think anyone is saying that you cannot recover, certainly what I am saying is that, if you teach your "subjects" how avoid it in the first place then you ought to be able to dispense with this unnecessary training risk. You could be falling into the trap of thinking that because you can enter and recover in an R22, that the same will work for all other models, it may not. There are many variables affecting VRS and recovery from it.

[3top]

Hi all,

I don't know what all this fuss about emergency training is.

VRS is not a scary thing to practise if you do it right - at least 2000' AGL, better 4000.
It only really gets scary when you get it where you shouldn't - short final, coming down too fast, going too slow and no ALTITUDE left to recover.

I always had a hard time to get into a decent VRS with any Robinson, but once in it, it is easy to demonstrate, that increasing power doesn't help, just makes it worse. It is this demo that is worth gold, as it drives the fact home, that power is worthless at this stage.
No one mentioned to enter Autorotation to recover - watch your MRRpm though. A proper demo and pre/after discussion of VRS will make any student aware of the dangers of a incorrect decent procedure.
At 3000-4000 it is no problem, but you will normally not get it there.
I never teach revocery by Auto OR Forward flight, it sounds like you have a choice of needing altitude OR go around. I ALWAYS point out, that you WILL need altitude, no matter what. I need a minimum of 400 feet from full VRS to "fly-out" - it also shows, that you have about 0% chance to get away if you get on short final.....

Same goes for EOL (does anyone do REAL EOL? I assume engine idle would be the thing...). How are you ever get someone to do a good auto if you never get them on the ground? Are you planning on damage anyway?

The situation seems to me like 15-20 years ago in fixed wing: "We don't need spin-recovery, because we train our students to never get into one!"
Well, WHY then is spin-recovery back in the syllabus??

Face it, initial training will always carry more risk for Helo-body-damage than regular flying. Well, part of the game.

Nothing to do whether your first ride is R22 or something else.
B-47s got lots of damage in training long before Frank knew about the R22 himself...

I am not in favor of NOT demonstrating Low-g anymore either, as it is a rather interesting experience. If you are never in it you really have no idea what to expect. So why is there no more low-g demo?
Because of the US-system of basic flight instruction. A 150-200 hr chap gets to instruct the next guy, having really 0 experience. He gets low-g demoed, next thing he shows his "new skills" to his student, chickens out (panics) half through the demo and ....crash.
No wonder FR pulled the plug on it.
I agree on this though.
What they should do, is demo it at their Safety-course, with the factory-instructor (Tim Tucker or whoever else is there now too....).
It is a rather harmless occurance, IF you know how to recognize and meet it, like retreating blade-stall and VRS.

Same should go for the VRS, don't let the green instructor kill his first student and himself with it, but let your 1000 hr+ chief-flightinstructor or better yet your 18K+ retired pro, turned instructor do the more complex/demanding demos and instruction. Cost? So what!!

Until you have full motion sims (I hear there is even a R22 sim under development...) realistically perform advanced emergency maneuvers, there is no substitute for the real training, including VRS, full-touchdowns autos, running ldgs/tkoff, stuck pedal, hover-autos, etc.

Enough ranted......


3top :cool:

[[email protected]]

TopendTorque - out of interest, the British military hasn't demonstrated vortex ring for very many years and doesn't even demo incipient VRS on any of it's many courses.

Why? Because, as Hihover says, if you teach your pilots how to avoid it then they won't put themselves in it.

I would suggest that military pilots operate in a far more demanding low-level environment than cattle musterers, especially with current ops in hot and high locations.

Yet we don't keep losing aircraft to VRS, how strange?

I have still to be convinced that you are actually demonstrating fully developed VRS in your aircraft - you imply you can enter and recover 3 times entering from 2000' and not going below 500'. That sounds like incipient VRS since fully developed VRS would give you several thousand feet per min RoD.

I know only 2 people who have encountered full blown VRS and they both took several thousand feet to recover from it.

[Thomas coupling]

There is definitely a misunderstanding of philosophies here:
IF you understand the aerodynamics of fully developed VRS, then you will naturally understand that the control of that helicopter has been removed from the pilot. It is an UNSTABLE state where the pilot has to wait for the a/c to remove ITSELF from VRS. It may choose NOT to do so!!!.
Fully developed VRS provides the following symptoms:
loss of control in all three planes.
ROD well in excess of 4000' +, even up to 8000'/min.
All qualified instructors (military anyway) are taught this in ground school. It has been removed from the UK syllabus for atleast the last 20 yrs, because instructors were crashing helos. Even then, they were demonstrating in ignorance, but atleast they started at 6,7,8 thousand feet in preparation for the horrendous ROD's.
Either you are talking about incipient VRS where you can still use the cyclic/coll/pedals and are experiencing ROD's of max 2000' ish, or you are extremely naive and plain negligent.:=

[oldpinger]

3Top-

Full motion sims don't have the flight modelling (yet I think) for vortex ring. I managed to crash the motion system on one once 'demoing' VRS. I also remember Incipient VRS generating pretty a impressive ROD.:ooh: on the annual QHI check.....

[topendtorque]

Thoms and Crab,
You guys have been around a bit.

care to explain just how after a rotor disc has fully developed its own bubble of vortices separate from the surrounding air mass, (VRS) which of course allows the disc complete with helicopter to fall at a diabolic rate, and then retain that bubble in the face of the equal and opposite diabolic rush of relative airflow?

and still be doing it many thousands of feet later? what were those idiots doing to fly into the gound (as you say) doing VRS exercises. see next para.

Care to also explain how an out of control helicopter can be flown out of VRS (as they say) by applying a cyclic control input?

Helicopters in VRS and near vertical descent trying to find VRS are still operating at 1G, unless i've missed something?

[eagle 86]

TT,
In the old days VR was near impossible to recover from - witness all the pictures of crashed Sycamores shown to us at the School. Modern design means that forward disc is more achievable - "blows", if you like, the vortices off the disc hence lessens ingestion - restores angle of attack, lower lever reduces angle of attack inboard to below stalling angle - requires lots of alt agl. Still wouldn't push a modern helo into fully developed VR.
GAGS
E86

[mountjoy]

I guess we've all seen the footage of the blackhawk, tailwind onto a moving deck, to the experts out there, was that VRS/SWP induced crash ?

[Thomas coupling]

Topentorque: eagle has it about right. The older heads on helos only allowed you to "regain" control, if, IF, that is...the selection of fwd cyclic was long and sufficient enough to "blow" the turbulence going on around the root and emanating outward...back away from the disc and placing you into cleaner air, thus allowing some form of recovery. Newer head design makes the above statement happen more quickly.
If you are able to confidently apply fwd cyclic in the knowledge that you will come out of VRS...may I suggest you are not in fully developed VRS:eek:

[[email protected]]

Topend, the theory goes that the root end of the blade is stalled because of the high AoA caused by the low speed of the inboard section and the high RoD.

The tip and outboard section is in its own recirculating vortex and not producing any useful lift.

This leaves the bit in the middle of the blade (a ring if you will, hence the name) which suffers unpredictable airflow due to the wandering of the tip vortex and the root stalled area.

The airflow coming at the disc from underneath is therefore somewhat erratic and causes random pitch, roll and yaw making control of the helicopter much more difficult.

This is one reason why some people say enter auto to escape VRS but you need a lot of height to do it.

Forward cyclic, if held long enough, should fly you out but , as TC has said, you really don't have much control at all.

The answer is to avoid the entry conditions and know how to recognise and recover from the incipient stage.

I think modern helicopters with higher hinge offsets and therefore more control power are probably easier to recover in - having said that they also have higher disc loadings and therfore need a higher RoD to get into VRS in the first place.

[topendtorque]

I've been away a bit, playing with CAT (18 degrees C) and carby heat (two thirds applied all day), winter rain, export boat deadlines, all fun stuff.

here is a reply.

Thank you for that EAGLE and others. With the hindsight of modern light rotorcraft behaviour and design I’d be delighted to discuss those old machine characteristics sometime. The sycamore (did they have tapered blades and or retreating leading edge?) must have been a funny animal. I dreamt about one once which in my comatose state turned out to be a Dutch windmill cavorting around. Maybe not so strange?

It seems that we are at cross purposes. You guys are talking about a characteristic which was described by ‘eagle’ and all the old text books as “settling with power”, with old style blade design and perhaps is also an inherent characteristic of some new designs, where you hurtle downwards at speeds up to 80 knots and unable to steer the damm thing around.

I am not.

Thomas Coupling quite rightly points out the confusions that arise in definition and I agree. We have all been subject to it, maybe because of references to the older generation blade / disc designs and the slowness of the text books / instructors to adapt to the change of new designs???????????

Of course we must also differentiate between types of helicopters as Nick Lappos points out in a recent article of his in the latest issue of a leading magazine.

Very few people experiment with these phenomena to the fullest extent which is fair enough if it generates a known and dangerous situation on types known for it.

Even on light types most people go to the edge of the ‘predicted’ (whatever that might be in the imagination)and teach students to stay away from that big dark phobia out there. Thus guaranteeing that neither the students nor they will ever progress for their own sake to really know their machine. That is dangerous for those who live in the low level environment.

However I am going to stick to my guns on this issue as it is one that we in the mustering fraternity meet often and unless one is prepared for it then it may hurt.

Old mate with his macho talk can bug off; perhaps he could study the video of the Seaking crash on the deck of a ship with its obviously unloading disc and tell me that there have never been any problems with incipient vortex ring state in his navy.

What I do, is demonstrate how VRS will hurt and then make sure the student can demonstrate his/her recognition of the incipient stage and then, their ironclad recovery from it, or, they don’t progress; simple.

I am talking about a situation that bites you in the backside if you are not careful which is a devastating descent for a short while, which happens with VRS. It is well described in the B/CA mag January ’84 issue by Dan Manningham, where he talks about “power settling” as a vortex ring state. Excerpts as follows:-

“Engineers refer to power settling as ‘vortex ring state’ because some air cannot escape from the rotor disc and becomes trapped in a ring shaped bubble that envelopes the outer rim of the rotor disc isolating it from the flow of undisturbed air. The vortex ring state occurs when the descent is nearly vertical and at a moderate rate. ---- but at some combination of moderate vertical descent speeds and moderate power setting, the upflow from the descent is approximately the same as the rotor induced downwash, setting the stage for vortex ring interference at the rotor tips. 300 to 600fpm is the range at which most helicopters are susceptible to power settling. Once the vortex ring has been created the helicopter will settle due to a loss of lift at the rotor tips. But if power is added to arrest the rate of descent, the increased energy at the tips will just add to the vortex ring and further degrade total lift.—---If the condition is encountered at a very low power setting, a rapid power application of full power may destroy the vortex bubble.. Nevertheless, if altitude is available the best technique is to push over to increase forward airspeed. At 15 to 30 kts the rotor will no longer fly in is own vortex-----“

This is what I demonstrate, as below.

One of the things that worried the heck out of me when I first started exploring the issue was what might happen to the relative AofA at the emerging recovery stage.

About then we started to hear about the horrendous R22 stalled blade stories. They had as their Highest Common Denominator, Low RRPM, and consequently not enough power to overcome drag and or retain blade rigidity.

Quite obviously while the machine is totally engaged in VRS in its totally isolated bubble of descending air then it is as safe as a house, the blade tips are not stalled. It is controllable in a disc sense because the blades are still operating at normal AofA attitudes. The disc has no idea that it is re-ingesting air, only we do because we are sinking with it.

However inside and with that bubble the machine must be falling at the acceleration of gravity which will only last for as long as that bubble of recirculating vortices can withstand the friction from the upcoming relative airflow.

THERFORE: - complete VRS will NEVER last for long, a couple of hundred feet in the biggest helicopters I suggest.

But what happens next? The M/R blade has to transition from that safe-house of normal AofA operation to one of a very high AofA coupled with a high G loading, which is required to slow the already gained massive RofD, not a happy situation.

At that developed state there is one coupled, advocated recovery, 1) collective down and 2) cyclic forward.

Re;-

1) a) Collective down presents the disc in flat pitch, as long as it presents itself purely as an unstalled item then it should prevail with some lift to slow the RofD down. I thought about the windmilling airplane propeller in flat pitch, it simply acts as a brake and slows things down, so to should the rotor disc as long as it retains its flat centrifugal plane of integrity.

b) By experimenting with quick stops I found that it didn’t matter how severely I did them, by presenting a flat disc to the relative airflow, there was never a problem with blade stalling.

c) All the time in the VRS practice I was juggling with the collective to keep the machine in VRS as long as I could.

2) a) This was more interesting. I found that inside the bubble of air the machine immediately started to fall toward the C of G, especially laterally, unless it was loaded symmetrically and then it fell toward the right (I.E. the gyroscopic precession in the southern hemisphere).

b) As I was initially doing it in a G5 by myself (for those who are not aware the driver sits to the left of the G5) I loaded the left litter and the fall to the left was very pronounced. I found that I could apply right cyclic to hold it in.
I found it easy to manipulate the disc at any time in VRS, so the forward cyclic for recovery is immaterial, any which way will do.

c) A tilted disc certainly makes the transition into clean air quicker and reduces the RofD quicker than from a flat profile when the VRS state simply “blew away.” This to my mind was because the reduced AofA of a disc tilted towards the relative airflow gave me a far lower AofA and thus a far higher performance value to work with rather than struggling with the disc still at high AofA and not wanting to go anywhere sitting flat ar**ed in a vertical descent.

I concluded that applying forward cyclic (or in any direction) is an ‘after the event’ process, which merely serves to help flatten out the RofD quicker if one has applied it earlier.

I reckoned to get out of any “worse situation”, one simply must use the further resources that one has, I.E. 1) roll toward gyroscopic precession, 2) use T/R to present the airframe as a drag moment to help push the rotor disc over toward the relative airflow.

It seems with the “settling with power” discussion with the old style rotors that what is needed is to get the AofA down by getting the disc tilted toward the relative airflow.

I understand the exasperation with the ‘tradition’ of trying to push over “forward” with cyclic. That is usually the slowest response direction of the cyclic. Certainly some quick rolling moment is required. With 8,000fpm = 79kts up yer trousers leg, yer could stick yer arm out the window perhaps?

Or maybe it might have been easier to attempt recoveries as explained above?

I think I should leave you guys to your discussions about “Settling with Power” where you do not talk about a single ‘vortex ring state’ but instead talk about a phenomenon that I have been unable to replicate in the R22 and B47 despite many hours trying.

I assume that you refer to the old textbook and the old style machines where the blade stalls from the root outwards and every thing turns into a big rout after that, no inferences meant.

Certainly any suggestion that a ‘fully developed VRS’ is where the disc is carrying one big vortex downhill at 8,000fpm is absolutely ludicrous. Perhaps your phraseology needs rephrasing.

The beginnings of either phenomenon could well be induced by a high DA situation where not enough performance, in either the rotors or engine, is able to arrest all measure of descent. This can be a perfectly safe environment and is often encountered. The trick is to keep that descent below 300fpm and not in the discs’ own rotor induced downwash. Shooting down its own tube, so to speak.

But, shooting the tube can be done anytime, with distractions aplenty and changing wind cues invisible.
That's sort of where i live.

[Shawn Coyle]

One of the first cues to vortex ring state that appears to be missing in this discussion is low frequency airframe vibrations - unlike those you get when transitioning back to the hover.
Always been the first cue in any of the numerous demos of vortex ring state I've ever done.

[[email protected]]

So topend - you are saying that you are right and that the rest of the known helicopter world is wrong.. I'm surprised there is room for your ego in the cockpit:)

If engineers call VRS 'settling with power' it is because they do not understand the difference between the 2 which is vast. And a 23 year old reference doesn't help your argument that we are slow to embrace new ideas.

There really is a fully developed VRS which will give several thousands of fpmin RoD and it won't go away in 200 feet.

You are either deliberately winding people up by posting b*ll*cks or you really do believe your own theories - which is worrying.

If a lot of R22s crash during mustering I would suggest that maybe it's because letting cowboys fly an aircraft that was designed as a commuter and is always underpowered is not a great idea (even if it is cheap). Excellent manoeuvreability requires lots of excess power, good control power and good control margins, none of which are demonstrated by the R22.

[NickLappos]

crab,
I fully agree with you - in the US the terms are used (improperly) interchangeably, even in texts. If you want proof, here is an entire Army that has the confusion:
http://www.dynamicflight.com/aerodynamics/settling_power/

The best definitions (IMHO):

Vortex Ring State [note - all ROD figures are for light training helos, turbines will have much higher VRS onset RODs]- when the aircraft forward speed is slow enough (below 12 knots) and descent is steep enough (faster than 700 fpm) that the rotor begins to consume its own downwash. In VRS, the torque oscillates and the aircraft bumps, pitches and rolls. In spite of pilot lore, VRS cannot be sustained at high rates of descent because beyond about -1200 fpm, the rotor is in autorotation, and not anywhere near VRS.

Settling with Power (SWP)- when the engine produces less power than the aircraft needs at the weight, altitude and hover condition. The aircraft bogs down, descends and is unrecoverable unless accelerated above translational lift. In bad cases the rotor rpm is pulled down by the enthusiastic pilot so that the tail rotor can also be swamped and a yaw can develop.

Why do pilot confuse the two? because virtually ALL VRS demos are began by descending slowly from an OGE hover, where the instructor is inducing settling with power by not raising the collective enough to stop the descent. In the typical training scenario, the instructor is demonstrating SWP at the onset, then as the ROD builds enough, he is showing VRS, then as the ROD goes to astronomical values (pilots love to wet their pants and brag about 4000 fpm) the instructor is actually demonstrating a vertical autorotation.

Myths about VRS:
Myth 1) VRS makes the aircraft descend so rapidly that the only way to recover is to dive out of it. Not true, if there is lots of altitude, the aircraft can simply be allowed to descend to vertical autorotation, where the rotor is eating clean air, and is powered by the descent. For light helos, autos are at about 1500 fpm, for heavier ones, 2 to 3000 fpm. For helos with lots of power, you can raise the collective while in VRS and motor up out of it. VRS typically raises the power required by something like 10 to 40% so this trick is not useful unless you are in a SkyCrane or a Black Hawk.


Myth 2) VRS causes the rotor to become dead aerodynamically, and if you don't do something, you will die. Only true low to the ground, the natural state of the helo in VRS is to accelerate downward until the rotor is eating clean air in autorotation.


Myth 3) If you descend in a hover at 300 fpm, you will get VRS. Not true, no helo will experience VRS at such low descents unless the pilot does nothing and lets the descent increase to real VRS speeds. At 300 fpm descent, the pilot is actually entering an artificially induced SWP regime, where the power is kept purposefully too low, and the descent is allowed to build.


Myth 4) High altitude or high gross weight makes VRS more likely - NOT true, the opposite is true, but since high weight and altitude make SWP more likely, it is easier to demonstrate the classic SWP becomes VRS becomes Autorotation demonstration that is labeled VRS by instructors and worshiped by students.

Myth 5) VRS occurs often and is a cause of many helo accidents. Not a chance, the conditions are very far away from where we operate (700 fpm downward, less than 12 knots). Most accidents where the VRS label is applied are mis-identified by the investigators, and are actually the much more common, much more dangerous SWP.

To recap: VRS is not what your instructor showed you, or at lease not all that he showed you. He demonstrated a complex SWP entry into VRS followed by a screaming vertical autorotation. In real life, the three distinct pieces of what he showed you are separate, controllable and in fact, very predictable.

[topendtorque]

Good point Shawn in a count of one to five for the time sequence of the airframe vibes, I’d suggest that the sinking feeling first comes in at about number three.

Crab, you must have had god awful day at the office,

you are saying that you are right and that the rest of the known helicopter world is wrong.

If you qualify the rest of the world as four people only on this forum who speak about the deadly characteristics of one helicopter type only, the pommy built sycamore, as the rest of the world then I’d suggest that you’re odds are a bit long.

I’m still keen to find out just what it is that it carries downwards for 8000 feet, a stalled set of blades perhaps?? A single vortex ring bubble it is not.


If a lot of R22s crash during mustering I would suggest that maybe it's because letting cowboys fly an aircraft

Regrettably this may be the statistics of the not too distant future, many cowboys are indeed getting themselves PHL’s and helicopters (10 in the NT alone in the last two years) and venturing into our increasingly unregulated commercial world out here and the result of course may be regrettable. However that is off thread. Many ex mustering jocks are flying worldwide with excellent cred.

So as far as ego is concerned I have no idea, I’m still learning.

that was designed as a commuter and is always underpowered is not a great idea (even if it is cheap). Excellent manoeuvrability requires lots of excess power, good control power and good control margins, none of which are demonstrated by the R22.

You obviously know so much about the underrated, over powered, highly manoeuvrable R22 that it’s not worth my while presenting another side. As a commuter, only, you should get out and read more; it might be a commuter in less than five percent of its world market.

As I have said before anyone who under sell the R22’s inventor’s intelligence so much by saying that ALL he was ever designing it for was as a commuter, than they must be indeed a poor judge of character if not downright insulting?

Nick, I think most of your points are in confirmation with mine. Also the entire army you talked about may be same one that gave rise to Manningham’s article because of their “approaching to land crash statistics” over a ten year period.

The highest common denominator being those in calm winds despite a cross section of operations and aircraft (all of which had sufficient power to hover OGE).

It’s a great pity more practice had not been done to prevent that. Remember the important point, done at ab-initio to recognise and avoid is most important, there is no need to try it on later in big aircraft.

The only reason i teach it is because slack instructors have not.

[Thomas coupling]

Are we agreed then topendtorque that you actually teach "Incipient Vortex Ring" and not VRS?

SWP has a lot to answer for, methinks

[eagle 86]

TT,
I suggest you stop doing what you are doing because you obviously don't know what you are doing!! I used the Sycamore as an example of early crap blade design (based on a fixed wing) merely to demonstrate that modern design has improved helicopter handling immensely. I've been teaching this **** since 1972 and I think I know what I'm doing (as does Crab et al).
GAGS,
E86

[[email protected]]

OK Nick now you have confused me (it is easily done:)) - how do you get to vertical autorotation without lowering the lever? To get into VRS you have to aggravate the incipient condition by applying power thus worsening the root stall and the tip vortex. How can this configuration (presuming you take no recovery action) get you to a windmill brake/autorotative state?

Topend - only eagle mentioned the sycamore and only once, all the other comments have been regarding modern helos.

As for the R22 - with anything other than one person on board it has a woeful power margin unless the fuel tanks are empty or you are in the habit of ignoring the MAP limits. I believe Frank himslef stated that his intention was to produce an affordable helicopter for the masses (a bit like the VW Beetle) - but it gets used for all sorts of other things because it is very cheap to run compared to a turbine helo. I also believe it is used most for training and private use.

Can it be chucked around? yes. But don't try to compare that to really manoeuvreable helicopters like Lynx, Commanche etc. There are hundreds of pilots who think because the rotor doesn't drop off that they are not doing any damage operating the aircraft like that - the R22 was not designed for mustering and you guys only use it because it is cheap.

As for the office - well mine is in a big yellow Sea King and I get to rescue people in it, it's always a good day at the office:)

[NickLappos]

crab,

The real question to ask is "How can a helicopter be descending at 3000 fpm and NOT be in windmill brake state?" By definition, VRS can only exist around about 0.7Vi to 1.2Vi (give or take). Here is a plot for a jet ranger, where the true VRS (the dark oval) is clearly between 1000 and 1600 fpm:

http://webpages.charter.net/nlappos/vrs.jpg (http://www.safetycenter.navy.mil/MEDIA/approach/issues/jun03/vortex.htm)


http://www.safetycenter.navy.mil/MEDIA/approach/issues/jun03/vortex.htm


For a low disk loading helo, the position of the collective in a vertical auto can easily be high enough to be in the powered flight range.

[[email protected]]

Yes but we are talking about getting into VRS with lever positions so high that without the engine running, the Nr would decay rapidly - it doesn't sound like autorotation to me. If what you say is true then all the stories of aircraft falling out of the sky or taking several thousands of feet to recover are not true and all they had to do was wait and it would fly out by itself. Sorry but I will need a lot more convincing evidence than a Jetranger graph to disprove the accepted theory on VRS

[NickLappos]

Crab,
In a descent, you start with a mild powered descent, drop thru VRS and then into auto. I have done maybe 500 of them (for some reason, 0 knot autos is a big deal with the FAA).

The guys who tell tales of dropping at thousands of feet per minute are either in autorotation, or they are kidding (and they aren't kidding!)

[hihover]

Nick,

Would one of the variables not be the amount of power applied, ie, more collective in a governed aircraft? As variable as there are aircraft types.

Thus, if more collective were applied during the mild powered descent just as you are dropping through, the situation would be exacerbated and potentially find a state where there is enough power being developed to stop you dropping through and continuing in VRS.

Could that happen?

[eagle 86]

I think we are still being confused here - to recap - conditions for entry into IVR are 1. low KIAS < 20, 2. ROD > 200ft/min, 3. increasing power from minimum to a lot. What happens next? Witrh collective still under your armpit ROD rapidly increases to in excess of 5000 feet plus, airframe vibration, random yawing. What is happening aerodynamically? Outboard section of blade not producing lift due to ingested vortices increasing induced flow reducing angle of attack, inboard section exceeding stalling angle of attack, decreasing middle section producing insufficient lift. Recovery action - lower lever - yes entering auto even - forward cyclic to "blow" vortices "back" to prevent ingestion. Need lots of AGL. Lesson? Recognise conditions of flight required to reach IVR and take corrective action before fully developed VR is encounted.
Had this discussion with a VERY experienced mate yesterday and it was clear to me that he did not understand the regimes of flight that put him in the danger zone!
GAGS,
E86

[hihover]

Eagle,

By "IVR" are you referring to Incipient Vortex Ring? If so, yes there is still confusion, because you then go on to describe a developed VRS.

VRS is VRS, I personally believe there are variables which affect its severity and they range exactly between what you describe and what Nick Lappos describes.

I don't understand why anyone would be demonstrating anything other than a recovery at the incipient stage. I don't even believe that is necessary.

[eagle 86]

HH,
It's like spinning a fixed wing (which when fully developed is actually autorotation) - you demonstrate the flight situation which will get you into it, note the symptoms, demonstrate the recovery methods. What I am trying to do here is let young/inexperienced pilots understand what flight regime MAY lead to IVR/VR. And no I don't demonstrate VR but I do demonstrate IVR.
GAGS,
E86

[NickLappos]

eagle86,
You are just spouting the old myths ("to recap - conditions for entry into IVR are 1. low KIAS < 20, 2. ROD > 200ft/min, 3. increasing power from minimum to a lot."

The attempt here is to describe PRECISELY what VRS is and how to know/control/avoid it. It seems that my points below (post #42) are not clear enough.

Some facts:

It is impossible to get VRS at 200 to 300 feet/min rod.

It is impossible to get VRS at 20 knots airspeed

VRS is not a power-caused problem, it has little to do with power.

Over pitching (SWP) is so often confused with VRS that the two are a mish-mash in most pilot's heads, so we get quotes like eagle86 above. The common training guides are of no help, because they repeat the same mish-mash.

hihover,
The variability for different helos and rotors is tied into the disk loading, where low disk loading rotors have less downwash velocity (Vi) and thus can get VRS at a lower rod. Power has little to do with it, your instructor was confusing VRS with SWP, as does eagle86.

[[email protected]]

Nick, your posts are quite clear but you are debunking a big urban myth if you are essentially stating that VRS doesn't exist and that the aircraft will get itself into vertical auto if you do nothing after the incipient stage. If all you have to do is wait for the RoD to get to 1500'/min so the vortiex disappears then this is a very major change to accepted theory and I am very sceptical about it.

[NickLappos]

crab,
What I am saying is not a change from aerodynamic understanding at all. It is however a major change from the pilot mythology that has been allowed to accumulate, unchecked by anyone who actually understands VRS, for decades.

The article I provided in post 42 is an example, here I also provide the papers of Gordon Leishman from U of MD who, based on the V22 accident, became quite expert on the methods of analyzing the rotor flow:

http://www.glue.umd.edu/~leishman/Aero/vring.html

It is exactly correct to say that when the rotor is descending at 1.3 times Vi there can be NO VRS. When we demonstrate it (I have done so only about 1000 times!) we pass thru that condition (and of course also the .2Vi and 1.0Vi) and call the whole mess VRS.

Can the collective be up to your armpits in auto? Yes, in fact, and a verical auto, it will be fairly high.

[FH1100 Pilot]

VRS...SWP...who cares? It's all theoretical anyway. I mean, we never get into those conditions up high. Nope, either/or happens down low, at the bottom of an approach when there may be no time or altitude to recover. Bottom falls out when you're up at a nice, high 5,000' OGE hover? Here's the procedure:
1) Lower collective,
2) Get some airspeed,
3) Land,
4) Change shorts.

Bottom fall out when you're on short-short final to a confined area?
1) Instinctively pull collective all the way up,
2) Say to self (if there is time), "Thiiiiiis is gonna leave a mark,"
3) Wake up in hospital.

Oh, and another thing. Nick sez that it's a physical impossibility to get VRS at a 300 fpm RoD. Oh yeah? It would be nice if we flew inside of computer hard drives...or if we flew in wind tunnels. But we don't, do we? We fly in the outdoors (well, most of us do, except for that Hanna Reich chick, but that was a long time ago). And, owing to the rather chaotic nature of, well, nature, things don't happen with laboratory regularity and precision. The wind outdoors does not always blow consistently horizontally. There are drafts, both up and down. Now, stick with me for a sec', just supposing we're in a OGE hover, coming down at 300 fpm and we get an updraft of 500 fpm? This updraft lasts for, oh, a couple of seconds, tops. The rotor is now "seeing" a RoD of 800 fpm, no? Enough to incite VRS? Impossible? I think NOT!

I have read Prouty (and Proust, but Prouty was harder to understand). I have seen the actual derived-from-test-flights performance chart plots for a certain helicopter (hint in SN). And I know that the behavior (behaviour, if you prefer) of a rotor is erratic and unpredictable in the absolute. Graph plotpoints all over the place, in other words. Within a given range, of course, and the resulting curves are "close enough for government work" but there's always a "flier" or two or three...anomalies which don't get included because we like our graphs to have nice, smooth curves, not jagged, Alpine-like outlines that look like something off a heart-monitor oscilloscope. And, we humans like to "round-off" stuff whereas nature does not always see things that way.

Still, the difference between SWP and VRS is moot, and makes no difference whatsoever to the rotary-wing pilot. If you get into either at exactly the wrong time, it probably won't matter which recovery technique you try to use. And you won't have time to ask yourself, "Heyyyyyy, is this SWP or VRS?"

[Swamp76]

Interesting thread.

In one of my previous lives we did a lot of this type of training for a very good reason: our pilots were at risk and there many SWP/VRS incidents/accidents. We wanted to stop that.

We would get them to take us to 1500-2000' and enter a typical regime of flight (low ROD, low A/S, partial power) and hold it until the a/c would noticeably accelerate down, noting the warning signs it was giving us.

Once well established on the elevator ride down we would recover, generally with forward cyclic. Of particular note was how long and how pronounced the control input needed to be to recover. That was the key as the normal theory of cyclic recovery wasn't telling htem just how much would be required to recover, and how much of an attitude change would result.

The training was effective, they learned a lot. I would say it felt like a VRS not SWP but who am I?

We called it VRS recovery training. We did it in the R22, R44, B206, HU500, and AS350: everything involved in seismic work at the time. The incident rate went way down.

[hihover]

FH1100, I think you have it just about right. The academics of the two are almost meaningless in the operators' world.

I'm tending towards SWP being the end result of a VRS when that VRS is not corrected and the aircraft is generating enough lift to sustain the VRS and does not drop through into autorotation. It matters not. They sound the same to me.

I did get it at 4000' in the hover at night but recovery at the first sign of trouble was instinctive and very easy to fly out of.

[[email protected]]

Fantastic stuff Nick and it made my head hurt - but...even though you are at least a thousand times cleverer than me, there is nothing I can see that supports your argument. In the three single rotor examples, in each case a significant reduction in collective pitch was introduced to create the RoD - there was no opposing application of lever which you would expect a pilot to apply once he got the RoD and vibration associated with incipient VRS.

[eagle 86]

Aaaaah - overpitching - I wondered when this would raise it's ugly head! Overpitching is simply when you top out the N1/Ng whatever of a gas turbine (merely using gas turbine because most are familiar with terminology - happens in pistons as well) - in other words engine can give no more but you as a pilot keep pulling lever - drag on rotor system increases - blades slow down - lift is lost.
GAGS,
E86
PS I trained through the US Defence system - aerodynamics was over simplified to suit the "sausage machine" process. It wasn't 'til I attended the "School" that I gained a clearer understanding of helo aerody.

[ShyTorque]

I've until now refrained from getting drawn into the argument about ROD of 200 ft/min at less than 30 kts being "VRS" territory, but seeing as it keeps on being mentioned.....

The Flight Manual for my aircraft states, in the "Normal Procedures" section:

STEEP APPROACHES AND VERTICAL DESCENT MANOEUVRES

Low speed steep approaches (up to 20 kts) and vertical descent manoeuvres should be performed with a maximum descent rate of 900ft/min.

That is copied verbatim. I expect the manufacturer also allows a bit for safety, as per the term "should", and so gives a conservative figure.

Nick, thanks for your patience on this subject ;)

[[email protected]]

Shy, I would guess that your aircraft is a modern, high disc loading machine so the downwash velocity is higher than an R22 or Schweizer and therefore the RoD would have to be much higher to encounter VRS on yours than theirs. However, I think the 2-300 fpmin is far too conservative and belongs in the days of ultra low disc loading like sycamores and similar.

[ShyTorque]

Crab, correct on all counts. ;)

I think we now need to forget the Sycamore, even I can't remember seeing one airborne. I recall RAF teaching was 30kts & 300 ft/min for the Whirlwind; that type used to be taken up to 10,000 ft on the basic course (pilots wearing parachutes) to demo it, the climb taking most of the sortie. I was never convinced by the demo I saw; I must have blinked and missed it.

The later inadvertent developed VRS in the Puma over Forkhill after a long night hovering at Flight Level Nosebeed was much more interesting.... :ooh: )

Chalk and cheese for a decent modern helicopter. Even the little R-22 has a relatively high disc loading.

[[email protected]]

Shy - are you sure about disc loading on the R22? Higher disc loading requires more power and the Robbo doesn't have any...:)

[rotorfossil]

Mention of the Sycamore reminded me that it demonstrated all the symptoms and unpleasant effects of vortex ring better than any type I've flown since. Probably why the exercise was discontinued for a while. As an aside it also demonstrated ground resonance pretty repeatably as well. But then it was the first British designed useful helicopter.

[[email protected]]

And we are still waiting for the second:)