When practicing vortex ring.........

[Burr Styers]

As someone who has experienced VR for real, in the "I learnt about flying from that" bracket, I'll share this with you. My circumstances were coming to a free air hover, at around 2000ft agl, at near mauw, in a light 5 seat military helicopter. Was in a bit of a hurry to get back "in position" following a racing re-fuel. So quite a bit of flare to get the speed off, lever coming up, and all sort of coming together for that, free air, Hi-Hover feeling. Suddenly the VSI went south, the ASI started going the wrong way round the dial, and I had a horrible sinking feeling. The two things I did, in this order, was to dump the lever fully, and apply an awful lot of fwd cyclic.

The vsi passed 2000fpm and the response from the cyclic input seem to be taking forever, But eventually the airspeed did start to build - slowly. Once I had got 30 knots indicated, I carefully raised the collective, and fell it starting to bite, and the cyclic (following a test wiggle) was also alive again. I bottomed out, climbed back up, and got back into position a very shaken (shaking) person.

I fell vertically over a thousand feet, and recovered in the next few hundred. It wasn't big, and it definitely wasn't clever.

If you want to practice this, please do it from several thousand feet, over a completely flat, empty, "run on" friendly area. (And not the densely populated - full of baddies place that I did) Also consider the proximity and availability of the emergency services, whose expertise with shovels and brooms may well be of use.

Stay safe

BS

[Nubian]

Surprisingly many here with the impression that wind-direction has no effect.. at least during practise VR, ie. ''onset VR'' and that's what the tread is about ''When practicing vortex ring.....''

As a flight-intructor I used to do this demo and practise onset VR with the students. If you enter full VR, it is almost impossible to recover from it without loosing 1000's of feet, and frankly that is a too great risk taking, when the point of the exercise is to recognize the symptoms of VR and aviod getting fully established.

I did it at 2000ft into the wind, and turned 180 degrees.... what was happening to the ground beneath me, was irrelevant, however the extra couple of hundred of feet lost during the exact same recovery-procedure was the interessting part of the exercise...

Now, allthough the helicopter don't have a mind of itself, I do!

I think it has been discussed more in detail in an older tread as well.

Cheers

[Hummingfrog]

Crab I think you have a mix up in nomenclature.

Yes, and if you are moving backwards within that mass of air ie with a 5 kt tail wind,

Into/down wind is measured relative to the earth - hence the word wind.

Positive/negative airspeed is measured relative to the helicopter and has nothing to do with wind.

Your statement would be correct when "5kt negative airspeed" is substituted for

5 kt tail wind

HF

[topendtorque]

If you enter full VR, it is almost impossible to recover from it without loosing 1000's of feet,

What sort of aircraft? Given that VRS is simply a set of vortices circulating around the blades in isolation of the surrounding air mass and therefore the aircraft is in free fall, it will accerarate at G whilst it stays in VRS. Can you then expain how those vortices remain with the rotor disc in the face of the accelarating resultant airflow? Surely the limiting coefficient of static friction of that surrounding airmass must have an effect on those pesky vortices quite quickly?

Perhaps the aircraft you are quoting falls or progresses into another type of 'failed lift scenario', other than VRS if I may use such a term? Did your aircraft have tapered blades for example?

I have always found 2,000 feet quite safe, higher if you wish to explore further, in and out of VRS.

I doubt there would be much difference between doing it all and recovery into the downwind or into wind condition, maybe a few feet, big deal, it is just that it easier to get caught if moving in the direction of the wind.

From the students achievement point of view I always see it as important to teach not only the actual characteristics of VRS and recovery, but to progress that strongly with many of the "circumstances" that will trap the unwary in low level flying.

A maneuvre I demonstrate and later ambush pilots with is to give the following set of three conditions. Travelling in the direction of the wind, I.E. Downwind, Decreasing airspeed and Descending, all at once. Feel the hairs rise up on the back of your neck just thinking about it.

I liken it to Drinking; Driving and Death; three D's together.

If one wishes to descend while travelling downwind, use collective only, keep the cyclic forward with positive airspeed.

The subtle hazard of light headwinds or nil wind is another, by projecting your downwash in front of you in a fairly fast approach with flare then descending into it or; as in not seeing a sudden wind vortice that changes your wind status from head wind to tailwind when decreasing airspeed and descending at low level.

The Downwind condition I classify as moving in the direction of the wind, regardless of helicopter heading but at a slower Ground speed than wind speed. I.E. A negative or tail wind. To accelerate to translation from that condition takes more power than commencing from a stationary ground speed in either a nil or a light head wind. It's simply a matter of the aircraft mass having to move further before it takes up the power saving extra lift from higher airspeed.

You can measure that on the ground in distance and power used in the simple hover downwind vs into wind excercises. How many measure the distance as well as note power?

All good fun
tet.

[[email protected]]

HF - I believe what I have stated is what the OP was questioning so maybe his terminology caused confusion.

If you are in a 2000' hover over the ground and the wind is blowing from behind you, are you downwind or do you have negative airspeed? The aircraft will handle the same and you are still further from a safe speed to avoid VRS than if you were hovering into wind/with positive airspeed.

However, meteorologists refer to system relative wind to explain the formation of warm and cold conveyor belts so the term wind can be used in a non-earth frame of reference

TeT - if the root and inboard section of the blade is stalled and the outboard section and tip are immersed in recirculating vortices then there isn't much of the disc left to produce rotor thrust to oppose weight - that is full VRS. If you raise the lever, you exacerbate the problem as the increase in rotor drag can exceed the rotor torque and Nr will decrease. The helo won't accelerate indefinitely but it will fall faster - if you don't have enough time/height to recover you are stuffed.

Theoretically, if you have a powerful enough helo you can pull through VRS but the best option is to lower the lever to achieve the windmill brake state or autorotation.

[Hummingfrog]

Crab In my opinion you have negative airspeed in the example you quote. I think the term into/downwind only applies when you are near to the ground and the wind can affect what you are doing ie landing/turning close to obstacles.

In all other modes of flight we don't modify how we fly due to the direction of the wind ie we cruise at a set speed irrespective of the wind direction. (ok I know we fly at Vne when into a strong wind but that is for fuel considerations not aerodynamic)

HF

[[email protected]]

Well hover at 10' then, stationary over the ground, with 10 kts on the nose - you have positive airspeed and are into wind. Now yaw through 180 degrees maintaining station, are you down wind or do you have negative airspeed? You can't have it both ways according to your definition

[Hummingfrog]

That is downwind with negative airspeed as you are close to the ground so using the term downwind is acceptable ( you will always have negative airspeed at some point when slowing down/hovering downwind) if you go up and hover at say 1000ft then you only have negative airspeed as what you are doing is not influenced by the ground unless there is a 1500 ft cliff just behind you that you could be blown into!!

I believe as I said in my previous post we should only use the term into/down wind when the ground is playing a significant role in what we are doing. Doing a negative airspeed approach to a cloud top at 2000ft won't end up in a crash if you mess up. Doing one to a HLS downwind and messing up could be expensive

HF

[eddietodd]

Vortex Ring

This is the perfect answer listen to this guy he knows what he is talking about the aim of teaching and practising incipient VR is to teach you how and when to look out for it DOWN WIND.

[eddietodd]

Look you wallies Humming frog got it perfectly correct in post 6 listen to him he knows what he is talking about. He probably talked to me in the past.

[Helinut]

Why is the downwind leg in a circuit called the downwind leg, if when it is flown at anything from 500ft to 1000ft+? I think your wish to limit the use of downwind as a description is too narrow (speaking personally, of course).

You need to know where you are, relative to wind direction for a whole host of reasons and heights, don't you?

[nellycopter]

So keeping things simple,
Who is a yes and who is a no ? To my origional question....
Think of it as a test question ... Multiple choice....
Yes or no ??

[Hughes500]

I always find it very difficult to put a 300 into incipient vortex ring if flying into wind ( about 15 kts plus), unless you go backwards ( relative to the ground) as the wind has an equivlent of 15 kts fwd airspeed, helping to keep the disc into clean air thus no vortex ring or limited effect. Turn heli the other way and bring back to 15 kts airspeed ( downwind and relative to the ground) and the heli will easily get into vortex ring, as effectively you are in a hover and hence the disc will be in its own downwash as you descend.
Well thats my experience anyway

[chopjock]

Wind direction is irrelevant so NO

[HeloDrvr]

For what it's worth, this accident occurred during a factory-demo flight (and we all know that things never go wrong on demo flights ugh

Heard it was heavily loaded (got to show off those capabilities) and they were landing at a hospital in Salt Lake City, Utah- approx. 4,300'msl on a Summer day.

[[email protected]]

if you go up and hover at say 1000ft then you only have negative airspeed as what you are doing is not influenced by the ground

yes it is because you use the term hover, which implies being stationary relative to the ground - unless you use the term relative hover - alongside a moving vessel for example.

This is turning into a circular argument (yes it is, no it isn't) but you wanted to be pedantic about nomenclature

[Camp Freddie]

the fact of the matter is that

1) if you try to make it look the same i.e a 0 ground speed situation into wind/downwind, it isnt the same and recovery will take longer from the downwind position as you will be starting from a negative rather than a positive airspeed

2) if you forget about the groundspeed and just concentrate on 0 airspeed, then it is the same it will just look different out the window, as you will have a greater groundspeed in the downwind situation.

[AnFI]

relative kinetic energy...

The answer's 'no'. Hummigfrog and Camp Freddie

Helicopter knows if it has horizontal airspeed component not whether it has a horizontal groundspeed.

But there is a but ....

If near the ground when VRS fully established then wind-shear will cause an increase in airspeed more rapidly in the downwind recovery case than the into wind case (when some airspeed is robbed by the shear).

Same reason downwind auto (surprisingly) is energetically superior ('cept for the running on part)

[eagle 86]

Adding fuel - settling with power/overpitching is not VRS!
GAGS
E86

[before landing check list]

Guys, wind is relative to the ground, not the helicopter. It is only when you are maneuvering relative to the ground ie pattern work does it make a difference. For example if it were completely dark, you cannot see the ground and there where no nav instruments to tell you otherwise, you would have no idea what your ground track is while you were doing constant standard rate turn (according to your turn indicator or compass with clock) while doing this in an airmass moving at 50 kts (relative to the ground). Your airspeed indicator would keep a constant indication, your altimeter would be unchanged, you would not feel a damn thing BUT your ground track would show weird loops moving in the direction of the wind.
You can be in a free balloon (untethered) in a hurricane and the ride in the basket would be overall quite. The helicopter does not care, the airplane does not care about wind UNTIL you are maneuvering relative to an object that is NOT moving ie runway, confined area, tree etc. Soooo your recovery from a VR state can be easily sideways, backwards, front (all relative to the wind of course) but front is easier since you can see where you are going which makes life easier.