Huey Can power out of VRS?

[Nealius]

I was just trying out some VRS recoveries in the Huey, flying up to 3,000' with about 75% fuel loaded, coming to a hover, reducing collective until vertical velocity is -2000 or -3000fpm with warning lights all coming on.

 

Then I found that by simply raising collective the Huey would just power out of it. Is the Huey engine really that strong? Or am I too light to really get into VRS with just 75% fuel?

 

Nope, still the same with 100% fuel. Also trying the Vuichard Recovery method, I totally max out my Saitek rudder pedal deflection and STILL can't keep the nose from yawing right. This is strange.

Edited March 7, 2018 by Nealius

[Gunnars Driver]

Nope !

 

 

IRL, no helo can outpower VRS. I dont know for the DCS-module, never tested how the VRS is simulated.

 

 

You don't outpower it, because the air is recirculating and more power only increases the rate of recirculation, and the sink rate.

 

 

First of all, Id say you have way to high rate of descent to get into VRS. The rate of descent must match the helos downdraft speed and helos with lower discload has lower downdraft and also reach VRS at lower vertical velocity.

The Huey hasn't that much of discload.

You need to be in the dangerous zone of sink rate but not to much sink rate, because you need your rotor to produce downdraft so the vortex ring can develope. Id guess you should try around 750fpm(just a rough guess based on disc load and comparing to other helos. Higher weight means you need a little more sin rate to catch the downdraft, because you are sending air down faster the heavier you are), and if or when you feel that the sink rate increases if you increase power, then you are there. IRL there also is increased vibrations and nose wont stat exactly still due to the tail rotor meeting disturbed air - I dont know if all these signs are modelled in DCS.

 

 

If in a VRS, you should be able to use full power and the sink rate just increases.

 

 

In real life its not that easy the hit the sweet spot and enter a real VRS.

What you described looks more like in real life not hitting the right position to stay exactly in the bad air.

 

 

Do you set the winds at altitude to zero ? If at high altitude, how can you be sure of hover exactly still, not moving at all ? I know that IRL it can take qiute some try's to find the "non sweet spot".

Edited March 7, 2018 by Gunnars Driver

[Nealius]

I'll have to check the winds, but I tried the same mission with the Mi-8 and could consistently enter VRS, and recover with the Vuichard method. With the Mi-8, there were aircraft vibrations like you mentioned, and the sink rate just got worse when I added collective.

 

I guess it's just harder to find that "non sweet spot" for the Huey.

[=Mac=]

I came across the Vuichard Recovery method on my own (in desperation, actually.) The idea is to break out of the "donut". The fastest way is to use both the rotor disc and the tail rotor. That's the Vuichard Recovery method. You don't have to go with your rotor torque (roll left or right depending on clockwise or counterclockwise rotor spin) but using the torque maximizes the escape.

 

I tried pitch escape (nose down or nose up) which seemed to "try" to escape. But it gave me the idea to try rolling. What I didn't know was to use rudder left or right to help the roll out of the "donut".

 

Simply trying to out power the "donut" only makes the "donut" stronger (if you get into one.)

 

I haven't tried this, but what you all are describing as a possibility is drop the collective, fall below the "donut" then applying power to stop descent. Sounds like something to play with but keep in mind the amount of time (or, more importantly, H above G) that trying to drop below the "donut" will require. I think the Vuichard is the best possible solution.

[Nealius]

I think I got it. Someone double check me. For some reason I can't enter VRS from a hover, but when transitioning from forward flight to a hover I will hit it.

 

Here's a video where I attempted twice, second time I showed the controls indicator in the top left. Still can't keep the nose straight during recovery; left pedal deflection is totally maxed out.

 

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[Flamin_Squirrel]

Then I found that by simply raising collective the Huey would just power out of it. Is the Huey engine really that strong? Or am I too light to really get into VRS with just 75% fuel?

 

You can't power out of VRS. Remember that the engine's only job is to keep the rotor spinning. VRS doesn't cause you to fall because of low rotor RPM; VRS causes you to fall because even though the rotor is spinning fine, it just isn't able to create any thrust (half the disc is stalled, the other is at a very low AoA so it doesn't generate any lift). If the rotor RPM is fine, more power won't help.

[Ramsay]

I think I got it. Someone double check me. For some reason I can't enter VRS from a hover,

 

Last time I checked in 1.5, the DCS Huey would tend to pitch down and fly it's self out of VRS from a static hover.

 

To see what is happening you really need to install the free Starter version of Tacview, as helps analyse these things.

 

... but when transitioning from forward flight to a hover I will hit it.

What I think happens is that, when landing/near the ground, we hold the helicopter level and don't let (or automatically correct for) the pitch down, so enter a deeper VRS.

 

I think the SAS of the Mi-8 might make entering a VRS easier for similar reasons but it's a different beast in so many ways and I really haven't looked at it's VRS behaviour in Tacview.

[Nealius]

So....a -3000fpm sink rate despite adding 90%+ collective while at 0kts airspeed (as in the video) isn't VRS?

[Chargeo]

The three conditions needed for VRS are:

Low airspeed

High rate of descent (-600 to -2000)

Powered flight (not in autorotation)

 

If you can power out of it then you are probably entering autorotation and then powering out of that.

It's actually quite difficult to intentionally enter VRS because part of what makes VRS so dangerous is that it is slow onset but fast to develop. Generally, you will be on the verge of VRS without noticing it if you aren't watching VSI and are flying visually. The natural instinct is to slowly and smoothly raise collective which worsens the situation, and this is often on approach which means there is only 1-500ft of alt to recover in.

 

If you abruptly pull full lever after being in VRS with the collective on the floor, you can force that air back through the rotor but at the cost of NR. If you have been in autorotation for long enough that NR reaches 120%+ then you will definitely be able to slap that air back through.

 

I hope this helps, this is my understanding of VRS.

[Nealius]

The three conditions needed for VRS are:

Low airspeed

High rate of descent (-600 to -2000)

Powered flight (not in autorotation)

 

 

Is that not what is happening in the video? I posted it for confirmation/feedback yet it seems no one is checking it....I'm starting to get confused with the back-and-forth about what is or isn't VRS without a solid confirmation of an actual attempt at it.

Edited March 9, 2018 by Nealius

[Gunnars Driver]

...coming to a hover, reducing collective until vertical velocity is -2000 or -3000fpm with warning lights all coming on.

 

So....a -3000fpm sink rate despite adding 90%+ collective while at 0kts airspeed (as in the video) isn't VRS?

 

If your question was refering to my post, see your first post: if you reduce the collective untill -2000 to -3000 fpm you should be autorotating.

With too little power applied there will not be a vortex ring developed, because you are descending faster than the downdraft air produced by the rotor.

 

If encountering VRS at good height, you can escape by simply lovering the collective to autorotative state.

 

I do not read your second post as being in the same state as the first. The second post, yes that sounds like VRS.

 

Most books ( and probably google searches) give a very broad band for when you are in danger of VRS. That’s because the theory must include all types of helos. ( And maybe a bit of not getting sued by someone that got into VRS outside the given values.)

Higher disc load( more helo weight per rotor area) means downdraft has higher velocity and this mean you will need to descend faster to get ibto the dangerous area.

Lower disc load leans risk comes earlier at smaller rate of descent.

A Robinson R22 will be in danger at a much lower rate of descent then a CH53.

 

It is possible to calculate the theoretical rate of descent for each helicopter type.

We got the numbers for all our AF helo types after we had one crash due to VRS some 15 year ago.

[Nealius]

Aha! Some people were mentioning VRS can happen if you descend faster than -300ftpm, others saying -750ftpm. When I get into what I think is VRS (my second post's state) I'm descending at close to -1500fpm.

 

I managed to find a thread where someone calculated VRS for a slick Huey with full fuel as being close to -1700fpm, which seems to match what happens to me in the sim. If I hit it just right, I will be descending fine and then suddenly lose power and drop.

[Flamin_Squirrel]

Yes it looks to me like you are indeed entering VRS in your video. Chargeo is correct about what is needed for VRS. By removing any of those three things you'll escape VRS. In your video you've achieved it by flying sideways (removed low airspeed).

[Gunnars Driver]

Aha! Some people were mentioning VRS can happen if you descend faster than -300ftpm, others saying -750ftpm. When I get into what I think is VRS (my second post's state) I'm descending at close to -1500fpm.

 

I managed to find a thread where someone calculated VRS for a slick Huey with full fuel as being close to -1700fpm, which seems to match what happens to me in the sim. If I hit it just right, I will be descending fine and then suddenly lose power and drop.

 

The conditions to get into VRS differs from the conditions experienced when in a fully dveloped vortex ring state.

 

To enter, you need enough power and rate of descend that cannot be too high( you need power applied).

When in a developed VRS, increased power/ collective causes higher rate of descent and maximum rate of descend inside VRS can be high.

 

Looked at the video, but only in ipad and i think it was hard to actually see if it was as a IRL VRS. To short time, and to small clocks...

I’ll test how the module behaves the next time fly the huey module.

[Nealius]

I played around with it more, and this is what I've noticed:

 

Descending at -1700fpm or thereabouts, with power, the nose suddenly kicks left and my descent rate rapidly increases. If I add collective before I reach -2500fpm or so, I will power out. If I wait until my descent exceeds -2500fpm, my descent rate accelerates beyond -3500fpm and I cannot power out.

[YorZor]

IRL you can get out of vrs with applying just power. But you'd need about double the power for a hover...

[Flamin_Squirrel]

IRL you can get out of vrs with applying just power. But you'd need about double the power for a hover...

 

Find that extremely difficult to believe. Source?

[heloguy]

Find that extremely difficult to believe. Source?

 

He may be referring to a source such as this one (taken from the US Army’s 3-04.203):

 

1-197. Recovery from settling with power may be affected by one, or a combination, of the following ways:

 

-During the initial stage (when a large amount of excess power is available), a large application of collective pitch may arrest rapid descent. If done carelessly or too late, collective increase can aggravate the situation resulting in more turbulence and an increased rate of descent.

 

-In single-rotor helicopters, aviators can accomplish recovery by applying cyclic to gain airspeed and arrest upward induced flow of air and/or by lowering the collective (altitude permitting). Normally, gaining airspeed is the preferred method as less altitude is lost.

 

-In tandem-rotor helicopters, fore and aft cyclic inputs aggravate the situation. By lowering thrust (altitude permitting) and applying lateral cyclic input or pedal input to arrest this upward induced flow of air, the aviator can accomplish recovery.

 

It’s never really taught as a recovery option, since getting into vrs unwittingly in the first place is a result of poor flying technique. If someone accidentally finds themself settling, it’s probably too late for the collective pull to save them. How much power would be required exactly would be a function of gross weight, and power available, with something above hover power certainly being required if no fore/aft/later cyclic is applied.

[Flamin_Squirrel]

Thanks. Doesn't sound like a wise move to me!

[YorZor]

Well there are three techniques one can use to get out of VRS:

1: Forward cycling, lower collective and get out of the dirty air.

2: Vuichard recovery - Set collective to climb power, pedal to keep straight and bank sideways into the updraft air.

3: Settling with power - Add collective and beat the air into submission.

 

Now, 3 is not recommended due to what heloguy posted. It has to do with the power required/available.

2 is a technique is that being taught more and more at different flight schools because it limits the altitude needed for the recovery because you don't have to lower the collective first (and thus start sinking even faster).

[Flamin_Squirrel]

Well there are three techniques one can use to get out of VRS:

1: Forward cycling, lower collective and get out of the dirty air.

2: Vuichard recovery - Set collective to climb power, pedal to keep straight and bank sideways into the updraft air.

3: Settling with power - Add collective and beat the air into submission.

 

Now, 3 is not recommended due to what heloguy posted. It has to do with the power required/available.

2 is a technique is that being taught more and more at different flight schools because it limits the altitude needed for the recovery because you don't have to lower the collective first (and thus start sinking even faster).

 

VRS is not a problem caused by a lack of power though. Pulling for more power will just increase the area of the disc that's stalled and lead to increased descent rate. It might work before VRS is fully developed, but if you got yourself into VRS into the first place I won't count on having that kind of awareness.

[Gunnars Driver]

I’d say that the large collective/ much power will not help when helo already is in developed VRS.

It is probably/maybe possible if descending but before VRS is fully developed, but it probably depends on how early you increase collective(= before entering VRS).

 

The vortex ring recirculation of air causes the angle of attack on the blades to decrease. This causes lower lift, and increased rate of descent, still high blade angle( but low AoA) makes the power demand high without producing lift.

Increasing collective causes a faster recirculation of air, and still low AoA= low lift.

It os not possible to outfly VRS with power.

 

Ill back this up with this:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060024029.pdf

( ”Model for vortex ring state inluence on rotorflight dynamics”)

 

I also have the complete series of R.W Proutys helicopter aerodynamics books. Got them at work, and I think he is a king on the subject, and he is aknowledged by all helo pilots I know.

I dont know if the books can be found online, but some articles for magazines on these subjects is found on the net. I’d say that if we find some difference between sources, R.W Prouty should be seen as the spurce of facts.

 

For example, the US army statement in post above is directly contradicted by US Navy NATOPS:

”The only solution for Fully developed VRS is to enter autorotation to break the vortex ring and when cyclic authority is regained increase forward speed.”

 

Digging to deep into this subject will make this a neverending thread. Threads like this already exists in IRL helo pilot forums.

Also,

Opening the discussion about VRS vs ”settling with power” will also make it last forever. Even different governments and avitation auhoritys cant get along so....

[YorZor]

Quote from a website since I can't post pictures from the textbooks here:

Power settling is an unstable condition. If allowed to continue, the sink rate will reach sufficient proportions for the flow to be entirely up through the rotor system. If continued, the rate of descent will reach extremely high rates. Recovery may be initiated during the early stages of power settling by putting on a large amount of excess power. During the early stages of power settling, the large amount of excess power may be sufficient to overcome the upflow near the center of the rotor. If the sink rate reaches a higher rate, power will not be available to break this upflow, and thus alter the vortex ring state of flow.

Normal tendency is for pilots to recover from a descent by application of collective pitch and power. If insufficient power is available for recovery, this action may aggravate power settling resulting in more turbulence and a higher rate of descent. Recovery can be accomplished by lowering collective pitch and increasing forward speed. Both of these methods of recovery require altitude to be successful.