Teaching VRS
 

Hi All,

Quick question, is it standard practice to demonstrate Vortex Ring / Settling with power recognition and recovery during helicopter flying courses. I was never actually shown it, just briefed on how to avoid, recognize and recover. Is practicing entry into and exit from VRS beneficial for flight training and if so what is the best way to demonstrate it in a safe fashion (downwind, heavy, etc?)

I would put this in the flight instructors forum but rotorheads never let's me down!

Any guidance much appreciated, as ever.

Eurocopter Beans

Both my Instructor and later the Robinson Factory showed me VRS in the R22.

If you are not shown how you going to know what the symptoms are like?

Incipient vortex ring state was demonstrated to me during my PPL course. From what I remember, we climbed to 4,000 ft and my instructor actually had a bit of difficulty trying to get into it.

Cheers

Whirls

It's a mandatory item in the JAR-FCL2 licensing syllabus.

It's hard to get demonstrate into wind in the R22 and requires a very high nose up attitude and backward flight. Weight should only affect the ROD at which it commences: bit heavier requires a slightly higher ROD to accelerate.

Lot's of height! 2k+ Downwind, decelerate towards an out-of-ground-effect hover. Keep the nose straight and attitude flat; allow the aircraft to accelerate the ROD slowly until it begins to race away: recover with disk to horizon and slight reductin of pitch. DON'T pull pitch until positive airspeed indicated.

I used to teach it in a past life, and think it is very important. We were in R22 mainly and also H300. We used to get plenty of height, 3000' feet or more, and pull it up in the hover. For some reason hovering downwind seemed to help (probably because into wind you still might have had some forward speed). Then, slowly and progressively start lowering the collective to descend whilst 'fishing' around for your downwash as you descend with cyclic. When you got it in the sweet spot it would fall out of the sky in the blink of an eye. After doing it countless times, I could tell by the feel when we were close to it and in the danger area, and think this is valuable knowledge to have. It would enable me to recognise and react far quicker than if I had never experienced it.

For those of you who haven't been there, why don't you post what you have been taught? I'd be interested to hear what they say if they only do it in the classroom.

You can't learn it all from a book.

for my FAA CPL checkride i had to demonstrate it in an R22 and recover from confirmed symptoms into stable forward flight before height loss exceeded 500ft

Chester:ok:

Demonstrating it is a standard part of the FAA PPL(h) checkride, you're taught to recognize it and how to get out of it from an early stage in the US.

Some examiners ask for a verbal explanation, rather than a demonstration, as they're not so keen to get into it in the first place.

VRS
 

It was never fully shown to me. During my PPL and in the Robinson Safety course only the on set (vibrations), recovery was explained, not shown.

I got since then several full blown VRS's, mostly while doing high altitude hover pedal turns. As been discussed before in other threads this is due to of a tail-rotor wake interaction that increases the risk (R44-B206), see other suggestions of flying backwards.

Happy that VRS was explained to me, the explained recovery worked nicely...

Need to show? Personally I don't think so, one can just do a high altitude hover (2k+) and kind of show what to do without actually provoking a full blown VRS.

m2c

d3

This is not a big deal....For 135 training and checkrides I teach it to all my pilots and have them demonstrate it to me. The FAA requires 1500 feet, but in reality you can recover from the initial indications with less than 100 foot altitude loss. Working fires, the times I get into it is coming in hot to a dip site...so I, and the guys I work with need to understand the symptoms and INITIAL indications.....we would probably not recover from full blown VRS at 100ft.

Here is how I demonstrate it---may not be perfect, but it works for me:

I have the pilot fly the aircraft in straight and level flight and then execute a slight nose up attitude and reduce power to less than hover power and HOLD it. Do not do anything else---the aircraft will decelerate, (it may take a while), and as it comes below ETL it will start to descend....again just HOLD the attitude....this allows you to differentiate between the loss of ETL and incipient VRS. Once you feel the nose shudder, you can execute the recovery with less than 100 foot drop from that point.

There is NO need to scare the student/pilot....the purpose is for them to recognize the indications etc.....

I can't imagine NOT teaching it to a student... jeez, that's as basic (and about as exciting) as fixed-wing stall training.

From reading this thread and the previous one concerning VRS training in the military it would seem that the civilians teach incipient recovery but doing the same has gone out of fashion in the military, I would be interested to know why this is the case?

I was given an engine failure when i was nose down to get out of 'settling with power' in my Commercial check ride... that was something. and yes settling with power should be in training curriculum.

Gordy, I doubt you are in any VRS at all with what you mention. I suspect the shudder you mention is probably more to do with turbulent air/tip vortices impacting the rotor system perhaps?

I am no techo head, but my understanding is you need a ROD of around 50% or more of the downwash velocity to begin the enter VRS territory. The downwash velocity varies significantly with factors such as rotor design, RPM, density altitude and disc loading at the time. It can be calculated quite accurately.

Here is a quote from Nick Lappos when I asked him the question a while ago:

"To calculate the downwash speed (which is the reference for VRS for a particular helo) just take the disk loading in pounds per square foot and multiply by 210, then take the square root. That will give you the feet per second for the 1.0 speed value.

To be conservative, if you take a descent at 50 to 75% of that descent rate, you can avoid VRS.

Here is an example: For an R-22, disk area 498 sq ft, Gross Weight 1370 lbs, disk loading is 2.75 lbs/sq ft. 2.75 x 210= 577. The square root of 577 is 24 ft/sec, which is the average downwash of an R-22 (24 ft/sec is about 14 knots, or about 1440 ft/min).

This means that the R-22 can't get VRS above about 11 knots forward speed (75% of the downwash velocity), but also that it can't get VRS in a descent less than 700 ft/min (50% of the downwash velocity)."


My experience of VRS is a lot of vibration, very sloppy and compromised cyclic response from the rotor system and an enormous and increasing rate of descent, way beyond that of autorotation. "Lose your guts" stuff.

In my opinion, recovery from "full blown VRS" as you mention will take far more than 100 feet, and may not be possible at all, as the rotor may enter a complete stall if the ROD goes off the scale.

Just a quick example: If your ROD in VRS is say 2400 fpm (auto is around 1800 or so) that is 40 feet per second. So in your recovery it takes you 2 seconds to decide to lower the nose and it takes 5 seconds for the cyclic input to take effect and the airspeed to build beyond ETL, and 3 seconds to try and do something about your huge ROD. There goes 400 feet (or more) in 10 seconds.

I think what you are talking about is more like getting to the open door of the aircraft and deciding to close it before you jump. Once you have jumped, it takes a while for the parachute to open and stop your fall.

Just my opinion!

Coyote
In your example, if it takes 5 seconds for the cyclic to respond, how long would it take just to dump the collective? There is more than one way to escape the VRS.:)

Gordy - absolute rubbish! You can't demonstrate Incipient VRS without allowing it to show the pilot all the feedback effects [Which I hope we all are aware of].
This will cost atleast 500-1000' height loss! Slowing down inaccurately in preparation for the demo could cost you 100', never mind recovering before this amount of height loss :=
Your poor customers are going away thinking a slight judder and they are in IVRS!!!

Coyote: As an ex mil instructor and currently sim instructor on heavies, I agree with your observations.
What people dont hoist in is that during fully developed VRS the a/c is: OUT OF CONTROL. The pilot cannot take charge of the a/c. It will either crash or fly itself out of the state. The problem with the latter is that it could take thousands and thousnads of feet for it to allow you to regain control.

make NO mistake here. Fully developed VRS is UNCONTROLLABLE!

What happens in real life with these 'instructors' is that they actually demonstrate IVRS and not VRS.

People who search for the real McCoy especially at entry gates of 4000' and below are living on borrowed time IMO.:ugh:

Safety margin 2, 4, 6K or not at all ??
 

Thomas,

I do agree with your comments, but think that the safety margins depends on type of heli and CoG configuration.

I remember that there was a case of a Puma losing many thousands of feet before recovery (even more than 4K if I remember well), so full blown VRS here, no thanks...

Personally I think that the R44's relatively large horizontal stabilizer at the rear of the fuselage combined with small body inertia helps to create a nose down attitude (even without cyclic input). A B-206 does not do it that easy in my experience.

All comes down to making a balanced risk assessment in the teaching curriculum, see for example the fact that EC fenestron failures need not be practiced any more, because of unfavorable risk comparison.

d3

TC says: "Fully developed VRS is UNCONTROLLABLE!"

Ummm... try rolling off the throttle. You are only in a vortex because the rotor system is developing thrust, trying to push air from above into airflow coming up from below.
Go into auto, you fall through all the vortex and emerge into clean air, roll on throttle, with forward airspeed, and hopefully fly away.

A CSurely you mean lower collective and maintain throttle RPM? Rolling off throttle would loose RRPM if in VRS???

Chopjock, 5 seconds for the cyclic to respond AND gain some airspeed. Of course I am aware that entering auto is a recovery technique. However, it still takes time and height to gain some forward speed in auto and to then bring the power back in and arrest the significant ROD. You can't just enter auto and raise the lever again with zero airspeed can you? Entering auto does tend to improve the cyclic response though, I have found.

The point I was trying to make was I think it is crazy to think that 100 feet is enough to allow for a recovery from any form of VRS.