Transition from free flying to ground effect is quite violent.

[Frag]

Hi guys,

 

there is another thread about the Mi-24 spinning uncontrollably to the left, caused by the yaw autopilot ... but what I will talk about here is different.

 

First of all, I am not talking about a runway rolling landing here .... but rather a field straight landing. Let's say that you approaching clearing in the forest where you need to land. If I approach at a controlled slow speed, as soon as the chopper fall into the "ground effect" mode, it will commonly kick hard to the left and pitch forward ...making me losing control most of the time. My only way out it to put tons of collective to gain altitude to save me from crashing.

 

Briefly, it seems that the transition from normal flight to ground effect at slow speed has a very violent jerk to the left and forward pitch. The autopilot I use are for pitch and roll. I do not use the Yaw and Altitude autopilot.

 

Anyone else noticed this while trying to slowing descend to land on a pad or small area? Wonder if its a flight model bug. I find odd that a very well controlled descend turn out so violent out of the sudden. I do understand that the ground effect will apply forces to the chopper, but WOW it is quite aggressive! Am I missing something?

 

 

[Rongor]

It's not the ground effect causing the spin. It's the new power setting you achieve when applying more collective to get into the hover. It's tricky to apply the correct counterforce in time by applying more right pedal.

 

The ground effect is actually decreasing this problem, yet I would agree it's debatable how well ground effect is working with the current Hind in DCS.

 

Keep in mind: the slower your speed, the more you will have to counter the torque when increasing collective power setting. Coming to a stop in a hover (regardless wether in ground effect or outside) is certainly the most demanding occasion of need for (quick) antitorque.

Edited July 5, 2021 by Rongor

[Lurker]

The ground effect should actually be a cushioning effect that happens when you enter a vertical altitude above the ground that is roughly equivalent to the diameter of your rotor. In my case the Hind behaves as it should, when entering the ground effect it actually stops descending (or slows down by quite a bit). Are you sure we are talking about the same thing? 

Edited July 5, 2021 by Lurker

[xxJohnxx]

In my opinion the yaw spins are not caused by the autopilot but rather by being overloaded. 
 

If you have a full weapons load and full fuel you are overweight and the helicopter still flies, but the tail rotor has too little authority to overcome the yaw produced by the main rotor at high blade angles required for hover. 
 

During forward flight both the lower blade angle and the aerodynamic stability of the tail cause reduced tail rotor load, and therefore it can fly even when overweight. However, as soon as speed is reduced, yaw becomes uncontrollable. 

[Frag]

11 minutes ago, Rongor said:

It's not the ground effect causing the spin. It's the new power setting you achieve when applying more collective to get into the hover. It's tricky to apply the correct counterforce in time by applying more right pedal.

 

 

That does actually make sense. In that case, does turning on the yaw autopilot help resolve this (sorry away from my gaming machine right now LOL)

 

11 minutes ago, Lurker said:

The ground effect should actually be a cushioning effect that happens when you enter a vertical altitude above the ground that is roughly equivalent to the diameter of your rotor. In my case the Hind behaves as it should, when entering the ground effect it actually stops descending (or slows down by quite a bit). Are you sure we are talking about the same thing? 

 

 

Actually, after reading what you guys had to say. I do realize that the ground effect could in fact not be my problem. Like Rongor said, its probably the fact that I add collective to hover that start the spin.

 

I never really felt this in the Huey, even though you feel the transition when entering hovering state. But that kick in the Hind while approaching a small landing pad scares the shit out of me. I get more nervous landing than fighting in that beast.

[Rongor]

8 minutes ago, Frag said:

does turning on the yaw autopilot help resolve this (sorry away from my gaming machine right now LOL)

 

So far I only find conflicting reports on the functionality of the Yaw channel in its currents state.

 

 

8 minutes ago, Frag said:

I never really felt this in the Huey, even though you feel the transition when entering hovering state. But that kick in the Hind while approaching a small landing pad scares the shit out of me. I get more nervous landing than fighting in that beast.

I also struggle to improve my performance with slowing down or transitioning into hover.

Regarding the Huey, the Mi-24 is certainly a much more powerful machine and therefore the need of countertorque is way higher.

[Lurker]

Just make sure you are not overweight when going in for a hover, or vertical landing and you will be fine. For me the YAW AP works great when taking off and landing, again when I'm not overweight. Usually I don't even have to input any rudder pedal at all as long as I'm watching my vertical descent rate and am careful about wind direction.

 

Important: If you're using AP YAW ON when landing, remember that whenever you input any pedal the channel will turn off. This might cause issues if you're not really careful when you are transitioning to hover. Make sure that all of your corrections and trimming is done on approach. 

[Frag]

3 hours ago, Lurker said:

Just make sure you are not overweight ...

 

 

Ok I will take it easy on cheeseburgers in the next few weeks.

 

3 hours ago, Lurker said:

Important: If you're using AP YAW ON when landing, remember that whenever you input any pedal the channel will turn off. This might cause issues if you're not really careful when you are transitioning to hover. Make sure that all of your corrections and trimming is done on approach. 

 

Oh I did not know that. To be honest I did not used the Yaw autopilot for long. I concluded that it was causing more issues than good. But I will experiment tonight by setting it on an easy access switch on my hotas to see if it help out.

 

[stuart666]

5 hours ago, xxJohnxx said:

In my opinion the yaw spins are not caused by the autopilot but rather by being overloaded. 
 

If you have a full weapons load and full fuel you are overweight and the helicopter still flies, but the tail rotor has too little authority to overcome the yaw produced by the main rotor at high blade angles required for hover. 
 

During forward flight both the lower blade angle and the aerodynamic stability of the tail cause reduced tail rotor load, and therefore it can fly even when overweight. However, as soon as speed is reduced, yaw becomes uncontrollable. 

 

Ive just been flying the Deployment campaign from the KA50 someone modified, with singular lack of success landing for the tail rotor problem, and im convinced you are right. The weight was about 108 percent of total, still overweight apparently after having gone on the mission and come back. I lowered it to 101 percent, went around the block, came in and landed first time without any LTE problems.

 

I would not overook the possiblity that its also aggrevated by wind. I dont know if ED have modelled this yet or not, but I figure an aircraft with a tail rotor is more likely to be affected by  wind than the KA50 would be. Anyway, I approached along the line indicated by a windsock, and that might have helped too.

 

Its difficult to know what is really simulated and whats your imagination, but I certainly do agree being overweight is the main cause of the problem.

[nazradu]

The main problem with a heavy chopper is the power state that you need to hover. It's possible to get to a point, lets say 12 degree plus on rotor pitch plus a high above sea level landing zone where your main rotor needs to produce so much torque and needs so much power from the engine that your tail rotor can't produce enough force to keep you straight.

[S. Low]

Well I can’t say if it’s all 100% modeled correctly but yes the transition from ETL to GE is going to require a power increase and then a power decrease. You need to modulate the collective as casmo would say.

 

Heres a good video on it:

 

https://youtu.be/obENn8hraoc

[nazradu]

I tried to make a video about it but I am so drilled that I have trouble getting myself into VRS without reflexes kicking in XD

And I would not say that the Hind is more prone to it than other choppers like the Huey for example. 

It just lacks the visual clues. That's what makes it hard.

[Steinsch]

@Frag

This might help. Control indicators are on and will show more or less correct yaw and collective input when transitioning into hover.

 

[unipus]

You can see this torque effect even in stable flight. For instance, line up for a rocket or gun run, then try to make corrections using collective. Anything more than the slightest input will make it very difficult as it will effect not only pitch but also yaw. The blade produces an enormous amount of torque.

 

The other absolutely critical factor to understand is that the tail rotor and main rotor share the same power supply. In other words, if you have max collective, you cannot also have max tail rotor effectiveness. If you find yourself spinning left, then there are only two solutions: 1) lower collective to restore tail rotor power or 2) airspeed.

Personally, now that I better understand how it works, I find the yaw channel invaluable for easy and steady flying in almost all regimes, including takeoff and usually landing.

[jojo]

It is quite a complex phenomenon.

Indeed, we are quickly overloaded with the Mi-24P. The airframe empty weight is already high, with fuel and weapons it quickly adds up.

 

On top of weight, air density (altitude) can lead to loosing tail rotor authority before main rotor, and the wind can also send main rotor turbulent stream into tail rotor.

 

You will find a lot of tutorials on YouTube about loss of tail rotor effectiveness (LTE).

Just think about rotor spinning direction.

Russian helicopters rotors are spinning clockwise. Most of tutorials you will find are thought with US helicopters spinning counter-clockwise.

Just invert left and right

 

 

[Quadg]

the pedal you press to counter torque is known as the power pedal.

when you pull up on the collective you also need to push on the power pedal.

when you reduce collective you need to let it out.

its a muscle memory thing.

you need a lot more power pedal in the mi-8 and mi-24 than you do in the huey.

slow movements of the collective are easier to learn. as you require slower power pedal inputs.

also remember the dampener on the torque pedals limits your speed of inputs. so pull too fast and the pedals wont move quick eneough.

raising the collective also causes the nose to pitch up slightly.

and down when you lower it.

so moving the collective requires a steady adjustment of both pitch and torque pedal.

in the huey its more pitch than torque.

in the hind/hip its more torque than pitch. (you have pitch and roll SAS)