(Almost) Uncontrollable yawing to the left

[Avimimus]

Hello,

 

I keep entering a state where the helicopter yaws uncontrollably (or almost uncontrollably) to the left... after a few rotations I'm able to arrest the rotation and keep flying as usual.

 

What causes this?

[yngvef]

Are you using Yaw autopilot channel?

 

Also, flying slightly backwards and/or sideways (or having the wind from the side) can make Yaw difficult to control in my experience.

[S. Low]

Check your virtual pedals as they may be stuck in the full left position. Whether it’s a bug or not , you should be able to reset the pedal position with trim reset. Trim reset is by default double-pressing the trim button

[26-J39]

Check this video it will explain your problem.   :)

 

 

https://www.youtube.com/watch?v=-FlPdBP0Hws

[Frag]

39 minutes ago, 26-J39 said:

Check this video it will explain your problem.  

 

 

https://www.youtube.com/watch?v=-FlPdBP0Hws

 

Indeed it really clarified that auto pilot thing. The problem reported to the OP was happening to me a lot.

 

Thanks guys!

[nazradu]

1 hour ago, 26-J39 said:

Check this video it will explain your problem.  

 

 

https://www.youtube.com/watch?v=-FlPdBP0Hws

I am glad it's usefull. Thanks for spreading the word bro

[26-J39]

7 minutes ago, nazradu said:

I am glad it's usefull. Thanks for spreading the word bro

 

No problem, had to be done!!!   It really helped me too!   

[leapingrodent]

20 minutes ago, nazradu said:

I am glad it's usefull. Thanks for spreading the word bro

 

It is really helpful. Thank you. 

[rayrayblues]

I am so impressed that I had to make my own video. My settings also seem to make a difference.

No more spinning like top when landing. No more crazy yawing on takeoff. No more drifting 

off course, etc. Thank you @26-J39...  

 

 

[26-J39]

No problem rayrayblues.   I watched the vid.   Nice work!!

 

The only thing I'll bring to your attention is that you don't need to turn the Yaw channel off to make turns.

When you step on the rudder pedals the Heading hold will be disabled.

So to initiate a change in course just apply smooth pressure the the pedals in the direction of the turn, as you straighten up ease off the pedals and Mi-24l have her new course set in the AP.

 

[rayrayblues]

2 minutes ago, 26-J39 said:

you don't need to turn the Yaw channel off to make turns

 

I know I can, but for me I can set a new course without the AP, since I'm also using the rudder trim, then

I lock it in with the AP to hold the course. Thanx again for your help.

[26-J39]

3 minutes ago, rayrayblues said:

 

I know I can, but for me I can set a new course without the AP, since I'm also using the rudder trim, then

I lock it in with the AP to hold the course. Thanx again for your help.

 

Everyone has there own style which is cool.

I use rudder trim too because i use racing pedals as my rudder pedals.   My Yaw channel never come off.

Have a great day ( or night)  Cheers

[stuart666]

I never use the yaw channel personally, but ive had the spinning effect. I think it may well be VRS on the tail rotor. Hard opposite rudder and slightly reducing collective seems to fix it.

 

There is a video here which seems to explain its occurance. The Hind it seems, is very squirrely in wind.

 

 

Edited June 29, 2021 by stuart666

[Wychmaster]

vor 2 Stunden schrieb stuart666:

I never use the yaw channel personally, but ive had the spinning effect. I think it may well be VRS on the tail rotor. Hard opposite rudder and slightly reducing collective seems to fix it.

 

There is a video here which seems to explain its occurance. The Hind it seems, is very squirrely in wind.

 

 

 

 

Can confirm that. I took off in a hot Mi-24. The yaw channel is off by default and I never use the trim nor do I turn on the yaw channel. In fact, most of the time I turn off all channels since there is also some pitch oscillations that occur sometimes and annoys me.

 

However, I made a hard break and got into a left spinning hover. Full right rudder had no effect. Was pretty hard to recover. I couldn't lower the collective because I was close to the ground and accelerating was also hard with buildings all around me. So I had to climb spinning until I finally had enough space to accelerate and lower the collective.

 

So my guess is, that it is either some unintended behavior or that they actually modelled LTE because of tail rotor VRS even though I recall that they said LTE wouldn't be modelled. Would be totally awesome if the "smuggled" it in

 

[Rongor]

32 minutes ago, Wychmaster said:

However, I made a hard break and got into a left spinning hover. Full right rudder had no effect. Was pretty hard to recover. I couldn't lower the collective because I was close to the ground and accelerating was also hard with buildings all around me. So I had to climb spinning until I finally had enough space to accelerate and lower the collective.

This is entirely possible without a tailrotor ring state.

Since you transitioned into a hover, and lateron into a climb, you caused a maximum torque at the mainrotor and therefore a maximum need of antitorque for the tailrotor. The trick is to not allow it into any left yaw movement at all why transitioning into the hover. The power of the tailrotor will be just that sufficient to keep your yaw controllable (if you apply pedals early, before letting a spin happen). In your situation you already had a left yaw moment. While your tailrotor would have had just enough power to keep your nose steady, it's just not powerful enough to stop a left spin in a high power situation (hover), which would demand even more power, much beyond the antitorque required to not get into a spin in the first place. 

 

IRL, If you are in a hover without any yaw moment, you are advised to generally only yaw into the direction in which you need to apply more power with you pedals, you don't yaw into the direction where you reduce power. Because of this exact problem. I don't know anything about the real world Mi-24, but there are actual operations procedures for several helicopters which prohibit or restrict use of pedals in low speeds and while hovering. Since the rotor spins to the right in the Mi-24, the toque will always try to pull your nose to the left. So whenever possible, during low speeds (hover), only yaw to the right. If you transition to low speeds and/or into hover, anticipate the left yaw and counteract instantly, don't let that spin happen. Your engines are already at their limits and your tailrotor won't be able to apply enough antitorque to stop that spin. They will perform just fine keeping you stead though. If you have to yaw to the left, do it with caution and slowly. The more weight you have, the more important this is.

 

If you let that left spin happen, you are overwhelming your tail rotor. It may not be able to catch that spin and neutralize it and this might kill you.

 

What you did was actually a good solution. Probably you faced a clear risk to hit some obstacles, but reaching for altitude to then pitch down and gain speed was indeed your only chance, well done!

Edited June 29, 2021 by Rongor

[Rongor]

On 6/23/2021 at 4:10 PM, Avimimus said:

Hello,

 

I keep entering a state where the helicopter yaws uncontrollably (or almost uncontrollably) to the left... after a few rotations I'm able to arrest the rotation and keep flying as usual.

 

What causes this?

It's probably just a matter of practice. You didn't tell us in which flight profile this happened. It can happen when slowing down and not applying enough left pedal. Stopping the rotation needs much more tail rotor power than preventing the rotation. When you will have gained a feel when and how much you have to counter increasing torque moment when slowing down, this problem will retreat.

[Wychmaster]

vor 8 Minuten schrieb Rongor:

This is entirely possible without a tailrotor ring state.

Since you transitioned into a hover, and lateron into a climb, you caused a maximum torque at the mainrotor and therefore a maximum need of antitorque for the tailrotor. The trick is to not allow it into any left yaw movement at all why transitioning into the hover. The power of the tailrotor will be just that sufficient to keep your yaw controllable (if you apply pedals early, before letting a spin happen). In your situation you already had a left yaw moment. While your tailrotor would have had just enough power to keep your nose steady, it's just not powerful enough to stop a left spin in a high power situation (hover), which would demand even more power, much beyond the antitorque required to not get into a spin in the first place. 

 

IRL, If you are in a hover without any yaw moment, you are advised to generally only yaw into the direction in which you need to apply more power with you pedals, you don't yaw into the direction where you reduce power. Because of this exact problem. I don't know anything about the real world Mi-24, but there are actual operations procedures for several helicopters which prohibit or restrict use of pedals in low speeds and while hovering. Since the rotor spins to the right in the Mi-24, the toque will always try to pull your nose to the left. So whenever possible, during low speeds (hover), only yaw to the right. If you transition to low speeds and/or into hover, anticipate the left yaw and counteract instantly, don't let that spin happen. Your engines are already at their limits and your tailrotor won't be able to apply enough antitorque to stop that spin. They will perform just fine keeping you stead though. If you have to yaw to the left, do it with caution and slowly. The more weight you have, the more important this is.

 

 

So the hard break lowered my rotor RPM, causing me to use maximum pitch to keep my altitude. This left me in a bad state where the RPM couldn't recover due to the high torque and the tail rotor didn't provide enough force to counter the spin.

 

The lowered RPM is an assumption of mine, since I had a fairly light loadout (only 2 gunpods) and was at sea level. In this configuration I don't need maximum pitch to maintain a hover and have quite good rudder turn rates to the right. Only other explanation would be that you loose rudder effectiveness once you turn to fast to the left (as you wrote) and can't recover from it, which would be some kind of LTE or am I missing something?

[lemoen]

Some of the missions starts the Helo in a state where the left pedal is trimmed some ways, and full right pedal doesn't give you the full right tail rotor. I've now started hitting the trim reset button as I get into a mission. I'm not using rudder trim.

[Rongor]

30 minutes ago, Wychmaster said:

 

So the hard break lowered my rotor RPM, causing me to use maximum pitch to keep my altitude. This left me in a bad state where the RPM couldn't recover due to the high torque and the tail rotor didn't provide enough force to counter the spin.

 

The lowered RPM is an assumption of mine, since I had a fairly light loadout (only 2 gunpods) and was at sea level. In this configuration I don't need maximum pitch to maintain a hover and have quite good rudder turn rates to the right. Only other explanation would be that you loose rudder effectiveness once you turn to fast to the left (as you wrote) and can't recover from it, which would be some kind of LTE or am I missing something?

You lost RPM because the engines where delivering power at their limits. Keep in mind that pulling the pitch lever isn't just applying 'moar' power. What is realy happening is that the angle of attack of your rotor blades is increased to generate even more lift. Increasing the AoA increases air resistance, so more power is needed to keep the RPM stable. There is a threshold at which your engines can't deliver more. So while allowing you to increase the AoA, your RPM will decrease proportionally.

 

Regarding the LTE, yes, not being able to stop the spin is some kind of LTE, yet you can say it is induced by bad piloting skills.

Also LTE isn't the same like tailrotor VRS. You didn't say this, but other people around here seem to mix it up.

 

What is important to know (and I am not sure this is conveyed by DCS manuals sufficiently or maybe simply nobody reads them) is that your helicopter main and tailrotors have interwoven power demands and share the same power source. There are limits which may shift depending on your flight envelope. Few people take time to understand these.

 

Let's be creative here: Say you are in that hover, slowly spinning to the left. Your helo is heavy and outside air is hot and dry. Your pitch lever is already under your armpit, engines are at their limits. Now you want to apply right pedal to counter that spin. While doing that, your main rotor RPM decreases. Many people would assume a bug. Not you. You know that right pedal will increase power demand. Since your engines are already at their limits, delivering power to keep that huge main rotor AoA to generate enough lift to prevent a descend, the additional power demand of the tailrotor is just too much, RPM decreases. You probably won't be able to stop that spin. Understanding all this is necessary to prevent states like this.

In a helo you have to anticipate stuff like this so much more than in fix winged aircraft.

 

 

6 minutes ago, lemoen said:

Some of the missions starts the Helo in a state where the left pedal is trimmed some ways, and full right pedal doesn't give you the full right tail rotor. I've now started hitting the trim reset button as I get into a mission. I'm not using rudder trim.

Exactly this made me stop using the yaw AP channel, as I noticed it can kill me by denying me full authority over right pedal actuation...

Edited June 29, 2021 by Rongor

[stuart666]

.

Edited June 29, 2021 by stuart666

[Wychmaster]

vor 24 Minuten schrieb Rongor:

You lost RPM because the engines where delivering power at their limits. Keep in mind that pulling the pitch lever isn't just applying 'moar' power. What is realy happening is that the angle of attack of your rotor blades is increased to generate even more lift. Increasing the AoA increases air resistance, so more power is needed to keep the RPM stable. There is a threshold at which your engines can't deliver more. So while allowing you to increase the AoA, your RPM will decrease proportionally.

 

Thanks for the explanation, but I have a strong background in aerodynamics and simultions, so I knew this already.

 

The whole point of my post was to figure out if ED actually modelled LTE and I triggered it or if there was an alternative explanation. As we figured out, a drop in the RPM is a valid explanation, since I needed more pitch to maintain a hover which finally resulted in me overstressing the engines.

 

vor 24 Minuten schrieb Rongor:

..., yet you can say it is induced by bad piloting skills.

 

Would rather call it: not enough expirience regarding the limitations of the new aircraft type and trying to dogfight another hind at low altitudes between buildings

 

vor 46 Minuten schrieb Rongor:

Also LTE isn't the same like tailrotor VRS. You didn't say this, but other people around here seem to mix it up.

 

 

To my understanding (from the video posted by Stuart666) my tail rotor not responding is a "loss of tail rotor effectiveness"  (LTE) with VRS being one of the possible reasons for it. If thats not the academic definition, its fine by me. As long as I know what is actually happens, I don't need to know its correct name

 

[Rongor]

1 minute ago, Wychmaster said:

To my understanding (from the video posted by Stuart666) my tail rotor not responding is a "loss of tail rotor effectiveness"  (LTE) with VRS being one of the possible reasons for it. If thats not the academic definition, its fine by me. As long as I know what is actually happens, I don't need to know its correct name

 

You got it right.

Correct name comes in handy though when conducting exchange in forums 

[Wychmaster]

vor 2 Minuten schrieb Rongor:

Correct name comes in handy though when conducting exchange in forums 

True... I am really good at logic related stuff, but language, wording and using correct terminology has always been my bane...

[Rongor]

Regarding the tailrotor VRS, inducing factors (for the Mi-24) would be hovering or slow speed in a strong crosswind from the left or flying sideways to the left.

[Avimimus]

3 hours ago, Rongor said:

It's probably just a matter of practice. You didn't tell us in which flight profile this happened. It can happen when slowing down and not applying enough left pedal. Stopping the rotation needs much more tail rotor power than preventing the rotation. When you will have gained a feel when and how much you have to counter increasing torque moment when slowing down, this problem will retreat.

 

I think it tended to happen when I was going >100km/h in one direction but managed to get the helicopter's nose facing more than 100 degrees for the direction of travel... sometimes I'd succeed in slowing down and turning around - but would then end up spinning two or three full circles.

 

It could be some form of exotic VRS in level flight leading to a loss of tail rotor effectiveness or it could be that I've somehow confused the flight control system... or I wasn't leaving enough power for the tailrotor... the thing which is most odd about this behaviour is that it'd fix itself if I let the helicopter pirouette enough times. That seemed much more curious than the fact that I'd somehow broken the helicopter.

 

I have found that the double-tap of the trim reset seems to help... but it might also be just that I've found other ways to fly the helicopter like an idiot which allow me to do even more reckless turns without losing control.

Edited June 29, 2021 by Avimimus