Downwind Quickstops
 

DTP,

To answer the second half of your query, have a look at this thread here:

Hovering Downwind

Essentially, it doesn't actually require more power to hover downwind. It's just that slightly poor handling on the part of the pilot can tend to consume more power.


I'll let the assorted aerodynamics experts answer your first query.


HTH,

B73


Oh, even if your textbooks don't have the answer, the subject might well have been discussed on here already. Remember, the search function is your friend! ;)

They are not dangerous if you know what you are doing. They are a bit harder though. The main thing that springs to mind is when you stop with a tailwind you are flying backwards. You may find you are caught out by weathercocking and end up inadvertantly rotating:eek:
You only have a rate of descent when descending and you should not do that until the quickstop is finished.
edit: Oh yes, I THINK the tailrotor consumes more power holding the tail into wind but I have never noticed it as a practical effect. I spend more time looking outside when hovering downwind than examining MAP gauge for small changes.

edit again. I just read one of Nicks post and he says it doesnt.

... seems obvious but ain't necessarily so when talking quickstops and vortex ring...

..... the problem of "rate of descent" when approaching vortex ring is in fact flow upwards through the disc opposing induced flow (hence "power on" being a prerequisite for vortex ring)...

... in a level flare with forward motion (aka a quickstop) you have precisely those conditions. And of course for all the downwind hover and rearward airspeed reasons you would have much more power applied if you tried to quickstop downwind.

Not sure why anyone would want to do a quickstop downwind, when a "flare and turn" of some sort can almost always be accomplished.

Did have a stude once try and quickstop (a heavy Wessex) downwind when invited to "do a downwind quickstop of your choice"....

... he was subsequently chopped! But not just for that...

TH, Ah semantics. Dont ya just love it. I would suggest a better phrase to describe what goes on in the flare as a change in the direction of relative airflow. Descent as a word is strongly indicative of going downwards.
I suggest you read nicks post (3) in this thread re: power requirements in the hover
http://www.pprune.org/forums/showthread.php?t=157371


By the way Its a gorgeous day. I'm going flying now.

Thank so far,

I don't WANT to do downwind quickstops but I just want to understand what happens.

TH: You have grasped the point that I was trying to make. In the flare the disc is tilited backwards. This surely has the same effect as a descent when you're moving forwards.

Now, with power applied, low air speed and this rate of descent I don't see why I wouldn't get into SWP / VR when INTO wind.

DtP

Is this the same fella who was asking about the backwards autos?!

Just quickly, if you fly a quickstop into wind, you start at high speed, reduce the power and flare. With wind on the nose and a low power setting, you're not likely to be descending (I use the term referring to the relative airflow) into your own downwash, and therefore are unlikely to get vortex ring. When at the desired speed and approach angle, you pull power and lower the nose to smoothly join the normal approach profile, again not a vortex ring risk.

However, comma, if you decided to do this downwind, you may find that when pulling power in during the latter stages of the manoeuvre, the tailwind sets up a condition where you're effectively settling into your own downwash, and you're in vortex ring close to the ground and in a bad way. I believe this was cited as the cause of a UK military Puma crash where they picked the wind wrong and ended up quickstopping downwind with a resultant prang.

There is simply no way that performing a quick stop will result in vortex ring state, because the rates of flow through the rotor are nowhere near the velocities required to cause vortex ring state. On the other hand, it is certainly possible to get yourself in trouble with the downwind quick stop if you don't carefully fly the maneuver. Why?

Because, when you bring the aircraft to a quick stop down wind, you first have to decelerate through 0 knots of air speed. And of course your power required its highest at 0 knots of airspeed, which you pass through somewhere short of the stopping point. This means the aircraft will sink a bunch at that 0 knot point, and ground contact is possible. Additionally as you pass through the zero knot airspeed, you actually begin accelerating rearward through the air so that the aircraft will start to try to point into the wind, becoming very unstable in yaw. This instability occurs right where the collective is being moved a bit due to the power required needs. As a result, you find yourself passing through the peak power point and dancing on the pedals at the same time. The chances of making a mistake are substantially higher than otherwise.

Typical quick stop problems include ground contact (especially the tail, because you are in a flare) and also poor yaw control. Overspeeds are more likely (big power changes) and sometimes there is a tendency for the helo to swap ends.

The old wives tale about vortex ring state being encountered while maneuvering near the ground simply will not go away. Let me specifically state that it is impossible to get into vortex ring state while maneuvering around the hover and performing maneuvers like a quick stop. Why? Because vortex ring state requires rates of descent of approximately 800 feet per minute to 2000 feet per minute, depending on the type of helicopter (actually depending upon the helicopter's disc loading.) if you achieve those descent rates near the ground, you have bigger problems than vortex ring state. The books that say that vortex ring state can be encountered in a 300 foot per minute descent are simply not correct.

Thanks Nick - That's what I was looking for.

Good explanation without mentioning "descending on a pocket of air" - and no that wasn't me

As a student we're told not to do these things and when out of the training school sometimes it can be embarassing to ask.

Its important to ask if in doubt.

Cheers
DtP

Downwind Quickstops
 

When I trained on the Bell 47, many moons ago, Downwind Quickstops did not involve stopping whilst still facing downwind but were, as previously suggested by teeteringhead, a low level flare and turn into wind. Quite exciting but safe if performed accurately.

I was always told that the biggest element of the manouvere that made it unsafe, was the tail stabilizor surfaces being pushed into the ground by the wind as your ground speed reduces. Try a 50 knot flare and turn, and you'll feel the downwind portion just doesn't feel quite right through the controls.

I'm afraid that I can't fully agree with Nick L when he says:
"let me specfically state that it is impossible to get into vortex ring state while maneuvering around the hover and performing maneuvers like a quick stop. Why? Because vortex ring state requires rates of descent of approximately 800 feet per minute to 2000 feet per minute".
On my type we fly quickstops nb 50 ft agl, and of course you should never see a RoD anything close to the 800 to 2000 fpm figures to which Nick refers, even if the quickstop is grossly mis-mandled and a RoD is allowed to build up during the manouevre.
However, as I see it it is not just the physical RoD as you sink that should concern us. As you flare the aircraft into the quickstop the angle at which the forward airspeed passes over (and through) the disc now changes. Consider it as a velocity, and take its 2 components (horizontal and vertical relative to the disc) and you will see that the disc is now exposed to an apparent RoD airflow that can be very significant. This apparent RoD airflow, allied to a sink during a mis-handled quickstop, could indeed lead to problems.
(I have drawn a lovely picture but I can't work out how to import it!)
It would be an extreme case that approached vortex ring parameters, but the difficulty that Nick described with the zero airspeed condition when operating downwind would only push you closer to this extreme condition.
Does that make sense?

Quickstops completed downwind
 

Maybe I am off track here but I always understood a downwind quick stop to be of the flare and turn/flare or turn and flare variety. Yes you enter the manouvre downwind but terminate into wind. It reads to me that you are talking about doing a complete quickstop from entry to completion downwind.
If this is the case then I am all ears but would not do one myself, then again as I said I may be well of the beaten track.
I shall wait to be enlightened.

gedney,
The VRS regime is where the rotor is fed a stream of air at a precise angle where the velocity of that air is 75% of the downwash velocity of the rotor. For a Robbie, this is about 800 fpm, and it must be aligned precisely at about 85 degrees angle of attack to the disk. ANY other angles or velocity and it simply is not VRS. If you achieve those speeds and angles while doing quick stops (85 degrees of disk angle to the air) you are really stopping quickly!

What most pilots call VRS is actually "too little power" and very nicely called "over pitching" in British parlance. A rapid power demand, faster than the throttle increase or engine accel, and the helo falls through, and the investigator pulls out his rubber stamp that says "VRS" and we have even more proof.

In reality, any discussion of VRS is a discussion of a rotor very close to autorotation (since windmill brake state is the next phase, and occurs about 120% of the downwash speed.) True VRS is extremely rare.

Couple of things...

1) VRS is not always about absolute rate-of-descent of the airframe. Remember the V-22 crash in Marana, Arizona that killed all those Marines? It wasn't that the ship was descending vertically so fast. In fact, the pilot still had "forward" airspeed. But this is deceptive. He also had the nacelles tilted backward (which I believe NATOPS now prohibit) as he was trying to decel/descend and maintain position on Lead, who'd screwed up the approach (and subsequently hard-landed his machine, a fact that was overshadowed by the crash of #2). It was this "apparent" RoD that the proprotors were seeing that caused them to start to go into VRS, evidenced by the roll instability the pilot experienced just before one of the proprotors "let go" into full VRS, putting the aircraft into unrecoverable A-VRS at which point it rolled pretty much inverted and crashed.

2) We need to be careful when we speak in absolutes. Although I generally do not like to disagree with Nick, when it comes to the absolute RoD's needed to induce VRS, one image sticks in my mind: That amateur video of the Canadian Sea King hovering around at the airshow in upstate New York. One minute he's hovering there, pretty as you please, camera steady on him. Next thing you know, it's falling like a wet turkey, blades coned up like a ballerina, tips nearly touching. (I wish I could find the full video that was shown on the local news the day it happened. The truncated clip that we see in the archival footage just doesn't give the complete story.)

I think that maybe nature doesn't always cooperate with our pat theories and "rules." I think that maybe a sudden gust...an updraft through the rotor can make it "think" that the whole aircraft is in a rate of descent. When that happens, if all the other stars are lined up correctly, boom-crash!

Downwind quick-stops to termination? Yikes, there's a scary thought!

FH1100,
That video is a screamer, I have found it a dozen times, but it is NOT VRS. The touchdown velocity of the helo precludes VRS. It is "over pitching" as can be seen by the slow rotor rpm among other things.

VRS is extremely rare.

I will post (again) the plots to show where and how it occurs, and let the debate run rampant (because it is a good thing!)

Nick

Can you clarify...

When we're practicing "settling with power", climbing to 2,000 Ft, slowing to zero airspeed (sometimes needing to induce a descent), raising collective and watching the VSi swing to indicate a descent of 1,200 fpm or more - are you saying that the initial indications are not VRS? From a safety point of view, isn't this a moot point, as we're trained to recognise the onset? Or is "real" VRS more perilous than what we actually practice?

I have heard that in some types - such as the schweizer, you're not really in VRS until the tail "drops away" behind you.

I can take my little ol' FH1100, go up to altitude, bring 'er to a downwind hover, get a decent descent goin', the pull up on the pole and watch it come down faster while not even getting near a power limit. Done it, in fact. Done it in a 206, too. Maybe VRS is a myth, or maybe it's "extremely rare" but I can experience "settling with power" any time I want to.

In fact, I used to demonstrate this to young aspiring commercial pilots. Photographer in the back, wants to shoot something on the ground from a certain angle - which puts you in the position of being in a downwind OGE hover and (of course) sideways to the object. You sit there, looking out the side window (not really at the instruments), maneuvering around at "the photographer's" command, "up a little...now back...down a bit...hold it there...down a little more..." Suddenly - whoa! - you find yourself in a big descent and pulling pitch doesn't stop it. It's a fine, easy, fun demonstration up at 3,000 feet, where the ground is nice and far away. But, I ask them, what would happen if you were only at 500 feet? It's an eye-opener, baby.

And yes, I have done such ball-buster photo flights. He says, "No, we can't be moving - I just HAAAAAAAVE to get this shot from this specific angle." And you go, "Yeah, but the wind is...I mean the ship doesn't...<sigh> oh okay, we'll give it a try." Hey, we were all young and stupid once. (Okay, some of us were.) Now I know better. Back then I didn't. Nobody took me up and showed me some of the wacky situations I'd find myself in as a commercial pilot, oh no!

So I dunno...maybe VRS, maybe not. Or maybe there's something else going on in the rotor system - weird flow transients or patterns that are hard to quantify and equally hard to understand. And come to think about it, a momentary RoD of 800 fpm in a hovering or descending Robbie might not be all that hard to produce. I mean, think about it. Think about being up at 400 feet and needed a whole 30 seconds to get straight down to the ground. Not a very fast descent, wouldn't you say? Doesn't seem all that amusement park-ish to me. Maybe VRS sometimes only needs a half-second of that to get excited.

Rotors are weird.

Thanks Nick, I’ve been hounding this “urban legend” for years. Let me take a stab.

Vortex Ring State (VRS) is a condition where the rotor ingests it's own vortices. This of course, is an over simplification. But what makes matters worse, VRS is a relatively unstudied phenomenon--just ask anyone in the V-22 program office.

During powered flight the airflow moves through the rotor system from above to below. When airflow is moving from below to above the rotor, we call this condition autorotation. VRS is entered when the flow is roughly between these two situations.

So it follows, to enter VRS, the airflow through the rotor needs to approach that of the rotor downwash. The rate of downwash is related to disc loading—but how fast are you entering this quick stop? More importantly, the movement of air needs to be nearly vertical through the rotor system. How far up is your nose during the quick stop? 85 degrees? Because 45 probably doesn’t cut it.

Now, it is typically understood that a helicopter is vulnerable to "Settling with Power" (I like the "over-pitching" term too) when the following 3 conditions are present:
(1) 20 to 100% power applied.
(2) Zero, or near zero airspeed (not ground speed).
(3) Rates of decent of 300 fpm or greater.
Isn’t this what you’re talking about (especially if your rotorcraft is underpowered and/or heavily loaded)?

VRS and Settling With Power are NOT the same thing, but are typically confused with each other because most pilots learn of them coincidentally. Doubt this? Think of it this way; if you agree about the 3 conditions for SWP above, then relate them to the conditions during a normal approach. Is a normal approach SWP? Is a normal approach VRS?

Wow!

It's awesome how much knowlage and information can be gained from this site.

My two cents with the down wind Quick Stop! Engine failure!


We MUST always be prepaired......

As you excelerate through transational lift, down wind and BANG!

Now you are down wind, low, with a ground speed that is not advised for touch down, do your best not to nose over on contact, maybe contact with slight nose up attitude, or any number of things that are waiting to bite us, and blade to tail contact is made. Reguardless, let's just say something get's bent. :mad: !

Mr. FAA inspector arrives and with his 15 minutes of helicopter experiance he determins that the action is unsafe because it was the take off phase and it was down wind! Then it's all bad!:ouch:

Most auto's with down wind touch down don't go well.

I recomend into the wind quick stop then hover drills back to the starting point. 20 years teaching folks to fly these things, ain't bent one yet (knoock on wood)!

Nick, will see you in Orlando! You continue to amaze me with your wealth of knowlage. I'm honored to know you.:D

A few factors could combine in a downwind quickstop to set up the relative airflow into the disc so that it would be coming in from underneath, perhaps leading to the conditions for VRS, I think.
As gedney said, the components of flow relative to the disc would be the important thing, wouldn't they?
Using Nick's figures of needing somewhere between 800 and 2000 fpm coming into the disc from 85 degrees 'below', I wonder if you could get that in a downwind quickstop?
Just crunching a couple of numbers in a scenario, say you were carrying out a quickstop into a pad with 10 kts downwind, got a bit steep (as you probably would) and allowed a rate of descent to develop, how about this - slowing down with about 20 kts groundspeed, subtract the 10 kt downwind leaving you with 10 kts through the air horizontally = 1000 fpm, approx. Add the vector of your descent, say 600 fpm, which gives a relative airflow from about 30 degrees below the horizontal. Also, you're flaring, maybe 40 degrees nose up (?) giving you about 1160 fpm of relative airflow coming in at 70 degrees from below the disc. Slowing down would continue to increase that angle, if you kept the rate of descent on.
As you pulled in power to try and save a very messy situation, you'd then have all the conditions for VRS, wouldn't you? Just a thought.

All i know is that the last checkride i did with a very experienced pilot, we went up to 3000 ft twice slowed down to zero , got the rate of descent up , pulled power .......and she started going up again !! Both times she did this so we got bored and did some other tricks. I think it is quite a difficult condition to bring on and more often the accident is too little too late ending up with over pitching.

works better with a tail wind if you can find one. I've also noticed a difference in older Robbies vs. newer ones...

how does the disk know its going backwards

I am a crusty ole long line pilot here in Canada and have been looking straight down out of all kinds of different machines over the last 10,000 hrs or so.

Since production longlining is pretty much all I do in all kinds of terrain I am often dancing on the edge of conditions conducive to vortex ring or just simply mushing due to the aircraft simply not having enough power to do what I have asked of it.

To me the defintion of vortex ring is when I pull collective and my sink rate INCREASES. Doesn't matter much what my vertical speed is because its more about relative airflow. If I pull power and my ass gets LIGHTER in the seat its time for immediate corrective action. Some may call this "incipient vortex ring" vrs full blown VR. Labels dont seem to matter much when it happens at a few hundred feet.


If I pull power and my ass gets slightly heavier in the seat, but I am still decending faster or more than I want too, then to me that is settling with power. This could of course get ugly and turn into overpitching if you keep pulling collective. It could also turn into VR if your sink rate increases.

DMNH

woccer woccer

"how does the disk know its going backwards"

it would be upside down in your case...

Dump the Pole. Most other posters seem to have become embroiled in a favourite Rotorheads topic of Vortex Ring.

Just to re-iterate what a couple have said: a downwind quickstop does not end with you hovering downwind. Imagine it as the helicopter equivalent of a handbrake turn in a car. You end up pointing in the direction that you have come from, ie into wind.

There are two types: flare and turn, and turn and flare. Heights and speeds will vary according to type. For a flare and turn, I would be flying downwind at 90kts and 50'. Initiate with flare, maintaing height and direction, and then start the turn into wind to end up pointing into wind with about 30-40kts still at 50'. Come to the hover, then forward and down.

For the turn and flare, same height and speed, but initiate with a turn and then flare off the speed during the turn still looking to be 30-40kts and 50'.

The difference between the two is the flare and turn gives you a (comparatively) long narrow flight path, whereas the turn and falre gives a short wide flightpath.

I'm sure others will have different techniques.

"There are two types: flare and turn, and turn and flare. Heights and speeds will vary according to type. For a flare and turn, I would be flying downwind at 90kts and 50'. Initiate with flare, maintaing height and direction, and then start the turn into wind to end up pointing into wind with about 30-40kts still at 50'. Come to the hover, then forward and down."



One word of warning, this is what most people might think that they are doing and come unstuck.

They start to flare, I.E. decrease airspeed, then sink, (as they wish to descend to the target) then pedal turn instead of cyclic turn, then they’re right where old mates DMNH and AOTW describes.

The only safe way to do it is turn with cyclic (steep co-ordinated turn) first half of the turn, and then second half of the turn as you are coming into wind commence the quick stop. Note how little power is reqd.

Now do it the other way that DtP first asked about (if you are stupid enough), note the power required, safety margins, and where oh where is that safe EOL picture?

AOTW describes the downwind VRS situation well and I suggest that there is no clear cut definition as Nick has isolated. That entry and many variants of it are just as good to get you sailing downawards and light on the seat. Why not look at a recent video of a seaking crash onto the back of a frigate or destroyer or some such. Note that he is sailing along in almost the same vortices configuration thanks to the ships superstructures, as AOTW describes, note the M/R coning flex abruptly two or three times as it unloads in incipient VRS.

As an analogy to the possible combinations reqd for LL VRS one might refer to a recent media report where some of the world best mathematicians finally gave up on trying to formulise the surf, breaking-wave actions.

I think that would be very simple compared to our rotor blades actions and reactions, not to mention the unseen winds vortices and currents afore you even got there.

At the end of the day when close to the ground, Downwind, Descending and Decreasing A/S, in the same handful is the same as Drinking, Driving and Destruction.

WW. No the disc has no idea which way it goes and it is also totally irrelevant as to which way the aircraft is pointing, the only relevance is the actual movement of the disc relative to the surrounding air and whether you might also be encountering or projecting vortices in front of it to then fly into.

There was a super good article in the Rotor and Wing Mag. (The Subtle Hazards of Light Winds) sometime in 1984, I use it as a bible and the numbers are nowhere near Nick’s, mind you it referred to light helicopters.

Nigelh, I agree at times esp. in the R22 in can be difficult to simulate and the running oneself out of puff and then overpitching, which is another story, is something that will get everyone sooner or later if they live close to the ground.
tet

I'm sure I remember being told on a flying safety course that the UK Puma accident mentioned on the previous page was vortex-ring related - obviously there could be a number of explanations depending on how much information the crash investigators had to go on, but it sounded plausible.
As Mighty Gem points out, the quickstop manoeuvre we want to fly starts out downwind and finishes into it, but the story with those guys was apparently late identification of the pad, picking the wind direction wrong leading to a quickstop that terminated effectively downwind, winding up with them falling through and hitting the ground in a scenario fairly close to the conditions I went through above, ie relative airflow into the disc at the right angle and rate to set up VRS.

Hi Dump the Pole... there is ample info here about Quick Stops but what I am amazed at is the primary factor that you have not been taught properly. I suggest that you bring this up with your instructor and if he/she has difficulty teaching quick stops in the correct manner and technique that you find an instructor that knows his/her trade. Really I'm appalled that the basic techniques are poorly taught.

Downwind Quickstop. Hmmm.
Well of course, you can do the handbreak turn thing - all banked over at low level - lots of fun - but you can also deccelerate straight downwind. It all depends on why you're stopping, and if it really needs to be a quickstop - lots of people simple incorporate the maneuvre into a rushed landing (fast approach > airtaxi > quickstop > land) I think most if not all of us have done that - after all, these things cost money and flying a 10 degree textbook approach into wind after a full pattern takes time.
As far as the aerodynamics goes - the Helicopter has no idea if its going downwind, upwind, crabbing or not - it simply flies relative to the body of air.
The only difference is when and how much power needs to be applied:
When you do a Q stop upwind, you never really get to zero A/S, so all you have to do is lower, then raise as you slow down - obviously your G/S will be lower.
When you do a Q/S downwind, you have to flare all the way down to Zero A/S (requiring more power) THEN you have to start accelerating BACKWARDS to get to Zero G/S.
This is obviously harder because it requires higher power, and downwind your G/S will be quicker, so everything happens much faster.
The key to downwind operations is to fully understand how much power you need at each phase, and to know your that airspeed can already be zero - even though you're nose-up and hurtling towards the pad at 20 kts!
The reason most people 'fall through' and crash is that they flare all the way to zero, then don't recognise it - and keep flaring, nose up, power down, then BANG.
Same reasoning goes for downwind takeoffs - anticipate that your power requirement will go up first, before it goes down, and be smooth...

Head Turner: I believe I was taught correctly (I don't do them !)

If you check my original question you'll see that I just wanted to understand WHY I shouldn't do a downwind quickstop.

Thank you everyone who has actually answered me and for the descriptions of correct technique and how to avoid having to do it !!

DtP

The amazing thing about pprune is the wide difference between all the separate helicopter worlds. This thread illustrates it quite well.

For small pistons, underpowered and flown by new guys, downwind quick stops are to be flown carefully or avoided.

For scout/attack helicopters, maneuvering low to the ground among trees and obstacles with some disregard for the wind is actually safer. When flying helos with good power and good controls, pilots who know how to use them consider that the norm.

The Real Lesson:
Please don't take the admonishment of good instructors talking to Robbie pilots as "natural" helicopter limits! And please obey those instructors until a Black Hawk or Apache comes your way!

DtP
Yours is a very valid q. and even though I refrained from talking about it before I also agree with everything that Rudestuff says. Except of course if the noise stops then lookout.

The following quote of his qualifies his story.

"The only difference is when and how much power needs to be applied"

May I attempt to explain that.

If you are doing a qs and slowing down in the downwind diretion you will get to the point where you are at zero A/S where you understand that you will need more power and further you are trying for a negative forward A/S, then that is where things go wrong for the unwary.

This is where the rudestuff quote comes in. Imagine the air that you are flying on as smooth above your rotor and very tubulent below it. Say that boundary between the two projects in a straight line in front of the disk. (If you are bloody lucky in the real world I say)

If you then apply enough power to stay above it you will be OK. Drop into it and you will be looking for all sorts of trouble, simple.

The limiting thing apart from all of the other eroded safety issues, is how much power do you have?

The same goes for doing pull ups into torque turns. When doing from the downwind direction to turn into wind it is real easy, as there is plenty of fresh air coming at your disk from behind you if you are stationary relative to the ground at the top of the turn.

When you do them the the other way from the into wind to the downwind recovery, always allow enough of a power margin to pull a bit of collective at the top so that the disk will be in fresh air. In other words plan to be travelling backwards a bit relative to the ground to give zero A/S.

It's can be kinda spooky if you don't. Remember what I said about being above eighty feet if you really stuff it up.

Doing anti-torque turns in the same manner becomes just a bit more complicated.

Nick: I'd like to see those charts, especially for the R22 as thats what I'm instructing in. If your descrption is correct, (and I'm not doubting you) I guess I've never been in actual VRS. I have never allowed a demonstration of VRS/SWP to develop past a 500 fpm decent rate which would mean that I wasn't in VRS by your definitions.

I find that when I induce SWP with a tailwind and I attempt to make it worse by pulling in power the helicopter (R22) has a reduction of the climb rate and an eventual climb. Certainly not true VRS if an increase in power is supposed to result in an increase in rate of decent.

So what am I really in? SWP but not VRS? I certainly am settling, have not reached a 800fpm decent rate, have power, and am yawing and shuddering until I recover.

I still teach that downwind quickstops are dangerous, maybe I'll just be changing the explanation of why from the danger of VRS and other factors to just the other factors. Simply put I wouldn't want any of my students making a downwind quickstop, regardless of VRS or not due to the other dangers already mentioned.

aclark79, I very much doubt you've actually been in VRS. What you seem to be describing is incipient stage, which is about as much as you need to demonstrate to a student. What you need them to appreciate are the dangers and symptoms. 500'min isn't much. Take it a bit further to see it develop. 2000'/min+! UK and USA call it two different things but it pretty means the same thing VRS or SWP.
Anyway, can someone answer this question:- Why do a downwind quickstop or any quickstop for that matter?
I always thought it was purely a dual co-ordination exercise whilst training.
As for those people who seem to blame every R22 crash on VRS, I say to them, it's probably because they don't understand many of the other possible causes of crashes close to the ground, but it's easy to just say 'oh yeh it was VRS'.

aclark79 said...Out of curiosity when 500 fpm was indicated how long were you stabilized? If your rate of descent was increasing rapidly, and you initiated a go-around at 500 fpm indicated your actual ROD was higher because of the lag in the VSI (unless you have an IVSI).


and now...

Nick swears that VRS can't be established as easily as most of us were taught, and I'm not going to argue with Nick, because he's almost certainly right, and I'm just repeating what I learned from books/instructors which could have been misinformed. It seems that there is an intermediate phenomenon which most of us call VRS or SWP, but some call incipient VRS which exibits the signs and symptoms taught to me as VRS, but without the actual vortex ring. Some have called this overpitching, but I was taught that term referred to a condition where the high pitch / AOA was creating more drag than the engine could overcome leading to a decrease in Nr etc...

Is it possible that while descending at very low, or no airspeed, the fact that we are descending into our own downwash causes such a reduction in angle of attack that we loose a significant amount of lift, even without the development of a vortex ring? (I mean more than just the loss of ETL, but an additional loss of AOA due to descending into air already accelerated by the rotor.) Additionally, in this state, would the addition of some pitch not give us the increase in AOA/lift that we expect, and therefore our rate of descent keeps increasing, and we feel that we are "settling with power"?

I ask because there is definitely a phenomenon when descending at at airspeed less than ETL whereby increased collective pitch seems to have no "bite", no increased lift... and it's quite disconcerting when near the ground.

Helimutt, Downwind quickstops (flare and turn / flare and turn as req'd) are taught to military pilots as a good method of arriving in a high threat area to a landing from a low level transit.

Yeah but no but yeah but no but ... Is there really a need for quickstops to be taught as part of the PPL syllabus, other than being bloody good fun!! :ok: One appreciates it is because the syllabub was derived from that used in military training but can't see it being much use unless I want to impress the blokes! :}

Cheers

Whirls

Whirlygig, you don't need to do quickstops to impress the blokes.

But I agree. Military may use it yes, but not many ppl (h) holders find themselves in a position which requires use of said quickstop. Never arrived into a hot LZ in a robbo myself. Although anywhere near Liverpool could be called that.:E

Hiro Protagonist, The term 'incipient' means 'beginning to exist or appear'. This means you are demonstrating the symptoms just as it starts but not letting it fully develop. That would be bad. Show a student what to expect and how not to be there in the first place. I guess after the incipient stage, there is only Vortex Ring State (Settling with power). It's not as easy to get into as you may think. But fully developed? :ooh:

I feel this is being done to death and there will always be people on the fence about it. A lot of instructors maybe just don't understand what they're teaching and make too big a deal out of it all??

I agree with Nick though.