new rotor model being created Yaw very unstable on the Apache

[admiki]

It's all great, but you are constantly moving the pedals and SCAS is trying to compensate.

Try that same flight with trim release held down and see if you get same behaviour. Then try doing what ShuRugal said.

[ShuRugal]

19 hours ago, Poptart said:

 

Appreciate the comments but you are missing some things here:

First, note that the green line in the control diagram is SCAS, the white line is my control input.

1. I am generally not doing more than 200fpm changes with the collective. The wild swings later in the video are because of the excessive movements of the tailrotor. At around :07 second I make a "big" input into the collective to increase to 400fpm without pedal input. SCAS makes a large correction and there is no felt yaw (correct behavior). At :12 I stop climbing by reducing collective and apply right peddal. No yaw (correct behavior).

At 0:17 I arrest my descent and the incorrect behavior begins. My nose should come right as the helicopter bites into the air and stops descending. There is no yaw (incorrect). At :21 SCAS (without my knowledge) is inputting maximum left yaw while the helicopter is no longer climbing. The helicopter's nose swings to the left. (Incorrect behavior the left pedal should not have that much authority and the helicopter lacks momentum). I stabilize with right pedal. (Correct).

At :30 I initiate a slow gentle climb (50fpm) I expect the nose to move left, it moves right because of SCAS (incorrect). 

At :40 I stop climbing and drop the collective expecting a big movement of the nose to the left. It occurs but is significantly delayed. I should be able to counter the leftward movement of the nose with collective. I cannot and I need big movements in the pedals to stabilize. (Incorrect). I'm also approaching 30 knots and ETL so the pedal movement should be damped from early in the video. It is not. (Incorrect.)

At :50 I make another big input collective input. Delayed yaw with the wrong force

2. I'm not chasing the yaw. I've never heard of PIO in the yaw channel with pedals.

 

This behavior is not present on any other DCS helicopter nor in real life.

Here is a video of me doing the same thing in the OH-58. This is a lighter helicopter in cold weather. All the behavior here is correct.

 

the FPM change does not matter.  what matters is how rapidly you are moving the controls.

based on the movement of the WHITE player-input-position indicators:

1. you are moving the collective up/down by as much as 10% of its travel in fractions of a second

2. you are moving the pedals by as much as 30% of their travel in fractions of a second.

3. you are making similarly jerky movements with the cyclic, but over only about 5% of travel.

 

Whether or not you can get away with this in other helicopters is irrelevant - other helicopters are not the AH-64.  You are not giving smooth inputs, you are causing PIO, and the SCAS is not able to keep up as a result.  Maybe you used to be able to fly like this in a previous patch and the SCAS was masking it.  Should the SCAS be quick enough and have enough authority to mask you rapid inputs?  I don't know.  But i do know bad technique when i see it, and i see it in your video.

Diagnose one problem at a time.  Make smoother and smaller inputs, give the helicopter time to react to your inputs, and then see if the unwanted yaw behavior is still there.

[Poptart]

1 hour ago, ShuRugal said:

the FPM change does not matter.  what matters is how rapidly you are moving the controls.

based on the movement of the WHITE player-input-position indicators:

1. you are moving the collective up/down by as much as 10% of its travel in fractions of a second

2. you are moving the pedals by as much as 30% of their travel in fractions of a second.

3. you are making similarly jerky movements with the cyclic, but over only about 5% of travel.

 

Whether or not you can get away with this in other helicopters is irrelevant - other helicopters are not the AH-64.  You are not giving smooth inputs, you are causing PIO, and the SCAS is not able to keep up as a result.  Maybe you used to be able to fly like this in a previous patch and the SCAS was masking it.  Should the SCAS be quick enough and have enough authority to mask you rapid inputs?  I don't know.  But i do know bad technique when i see it, and i see it in your video.

Diagnose one problem at a time.  Make smoother and smaller inputs, give the helicopter time to react to your inputs, and then see if the unwanted yaw behavior is still there.

That's not consistent with my experience in real life or any of the other helicopters in DCS (including the AH-64) before the patch a couple months ago. The hunting behavior of SCS at 0:26-0:40 is simply not correct. During that time there is zero movement of the collective. I've never heard of PIO yaw in any helicopter, ever. It's not a thing that exists in real life. In fact the heavier a helicopter gets the more impossible it becomes. There is just so much momentum that heavy helicopters have you could never induce such a thing because the tailrotor does not have that much authority relative to the mass to move like that. 

It's not about "smaller" movements the physics are simply wrong.

I repated the flight with the SCAS yaw disabled and the oscillations are gone but the forces are still all wrong. There is a large, unnatural yaw force that turns on and off at 20 knots. If you constantly go between 18 and 20 knots, you can get the helicopter to oscillate if you hit it at the right frequency. This happens regardless of torque setting. There is another unnatural force, smaller, above 27 knots in the other direction.  

 

 

 

Edited May 23 by Poptart

[HPLsCat]

I can replicate that wandering nose at 20 knots, so it's certainly a thing.

But is the Apache unflyable, or some of the other overheated rhetoric on this thread? No.

[admiki]

4 hours ago, HPLsCat said:

I can replicate that wandering nose at 20 knots, so it's certainly a thing.

Agree.

4 hours ago, HPLsCat said:

But is the Apache unflyable, or some of the other overheated rhetoric on this thread? No.

Agree once more.

[mason.zh]

On 5/23/2025 at 1:37 PM, Poptart said:

That's not consistent with my experience in real life or any of the other helicopters in DCS (including the AH-64) before the patch a couple months ago. The hunting behavior of SCS at 0:26-0:40 is simply not correct. During that time there is zero movement of the collective. I've never heard of PIO yaw in any helicopter, ever. It's not a thing that exists in real life. In fact the heavier a helicopter gets the more impossible it becomes. There is just so much momentum that heavy helicopters have you could never induce such a thing because the tailrotor does not have that much authority relative to the mass to move like that. 

It's not about "smaller" movements the physics are simply wrong.

I repated the flight with the SCAS yaw disabled and the oscillations are gone but the forces are still all wrong. There is a large, unnatural yaw force that turns on and off at 20 knots. If you constantly go between 18 and 20 knots, you can get the helicopter to oscillate if you hit it at the right frequency. This happens regardless of torque setting. There is another unnatural force, smaller, above 27 knots in the other direction.  

 

 

 

I agree, the SAS servo at low speed is quite unstable now. 
I would recommend 2 things for now:

1) Holding down the FTR instead of turning off the SAS.

2) Breakout the yaw SAS during the low speed flight (<40kts), for example if you need a little left pedal during the flight, keep the yaw trim reference to the right, if the pedal position is far enough from the "referenced position", the hold mode will temporarily disengage, this will reduce the chance of erratic yaw caused by the SAS. 

Combined these 2 tips together will make the flight a bit easier. Good luck! 

 

[[DE] T-Bone]

On 5/23/2025 at 8:37 PM, Poptart said:

That's not consistent with my experience in real life or any of the other helicopters in DCS (including the AH-64) before the patch a couple months ago. The hunting behavior of SCS at 0:26-0:40 is simply not correct. During that time there is zero movement of the collective. I've never heard of PIO yaw in any helicopter, ever. It's not a thing that exists in real life. In fact the heavier a helicopter gets the more impossible it becomes. There is just so much momentum that heavy helicopters have you could never induce such a thing because the tailrotor does not have that much authority relative to the mass to move like that. 

It's not about "smaller" movements the physics are simply wrong.

I repated the flight with the SCAS yaw disabled and the oscillations are gone but the forces are still all wrong. There is a large, unnatural yaw force that turns on and off at 20 knots. If you constantly go between 18 and 20 knots, you can get the helicopter to oscillate if you hit it at the right frequency. This happens regardless of torque setting. There is another unnatural force, smaller, above 27 knots in the other direction.  

Regardless of the fact that the yaw channel is currently oscillating a lot, I recommend keeping the speed above 40 knots on the targ tapproach. In practice, I have achieved good results at 50-60 knots.

Without heading hold sub-mode, the reticle can be aligned cleanly to the target with gentle pedal inputs without the system trying to push the aircraft into a different heading.