investigating New FM, pitch oscillations on supersonic speed

[Blackfyre]

Subject.
I do not have any real data, but these oscillations look and feel weird when doing a basic crank maneuver. Oscillations are less violent when you are slower. 

Added: on 0.9M it feels nice and smooth. I think the current FCS implementation can't keep up on 1.4+. Have added second track with full stick deflection.

F-18-oscillations.trk

F-18-oscillations2.trk

Edited March 18, 2024 by Blackfyre

[Rissala]

At supersonic speeds, the plane feels almost dangerous to handle since pulling over 10gs without touching the paddle switch happens very fast.

Here is a track where I do maneuvers at medium A/C weight and then at very light A/C weight. With some fuel and stores onboard and at supersonic speeds, the plane exceeds the G limit of 6.6 by ~4g with smooth aft stick.

With very light weight, the exceedance over the limit is almost ~3gs with smooth aft stick and ~6g with oscillations . The controls indicator is shown in the track.

Max G pulled at supersonic speed was 13.2g. I am aware that it is easy to go past the limiter, and that is completely understandable. This is IMO just too much. It takes the FCS around 1 to 2 seconds to catch up with the new state of the A/C and only after that can I pull full aft stick without having to worry about structural damage.

overG.trk

[BIGNEWY]

I will ask the team, but we will need to see evidence that it is incorrect. 

thank you 

[Blackfyre]

Any updates on this?

[Blackfyre]

@BIGNEWY, @Lord Vader, could you please give an update on this, especially in advent of new FM changes.
I haven't found any evidence that Hornet should not wobble, but I also have not found any clue that she should. Obviously, Hornet should be capable of flying 1.4+M and if she had such behavior, it must be mentioned somewhere as it simply looks dangerous both for pilot and aircraft. Also, it wasn't the case before major FCS and flight model update, was this introduced intentionally? If it wasn't, then it is a bug. If it was, could you explain why, please? Because to my mind it doesn't make sense for 4th gen fighter with advanced FCS.

[DummyCatz]

On 3/18/2024 at 11:23 PM, Rissala said:

With very light weight, the exceedance over the limit is almost ~3gs with smooth aft stick

Significant overshoot like this is a very unwanted characteristic and can result in low flying quality ratings due to insufficient damping of the short period pitch oscillation according to MIL-STD-1797A (https://www.scribd.com/document/49403406/MIL-STD-1797 with DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited).

If it's true then this is a design flaw of the FCS, that Level 1 or even Level 2 rating cannot be guaranteed.

Edited September 27, 2024 by DummyCatz

[NineLine]

19 hours ago, Blackfyre said:

@BIGNEWY, @Lord Vader, could you please give an update on this, especially in advent of new FM changes.
I haven't found any evidence that Hornet should not wobble, but I also have not found any clue that she should. Obviously, Hornet should be capable of flying 1.4+M and if she had such behavior, it must be mentioned somewhere as it simply looks dangerous both for pilot and aircraft. Also, it wasn't the case before major FCS and flight model update, was this introduced intentionally? If it wasn't, then it is a bug. If it was, could you explain why, please? Because to my mind it doesn't make sense for 4th gen fighter with advanced FCS.

As mentioned in last week's newsletter. the F/A-18C is undergoing a refactoring of the FM/FCS. Please test again one this effort is complete and let us know and If you still see issues, please reply back with tracks. Thanks!

[Blackfyre]

5 hours ago, NineLine said:

As mentioned in last week's newsletter. the F/A-18C is undergoing a refactoring of the FM/FCS. Please test again one this effort is complete and let us know and If you still see issues, please reply back with tracks. Thanks!

Thank you for your response. I fly a lot doing A2A and every time I suffer from these oscillations. I somewhat got used to it, but it severely reduces agility, since I have to do 2g turn instead of 3-4g.
Here is the new track, but nothing has changed in that regard as far as I can tell.

F18-supersonic-oscilliations.trk

Edited September 27, 2024 by Blackfyre

[Maverick806]

The patch with the FM/FCS changes hasn't been released yet. You should test again after the patch containing those improvements has been released.

[Blackfyre]

10 hours ago, Maverick806 said:

The patch with the FM/FCS changes hasn't been released yet. You should test again after the patch containing those improvements has been released.

Oh, stupid me, I've misread NineLine's message and read it as wanted it to be. I have been testing this after each patch ever since a new FM was released. So, I hoped this issue could be addressed (or at least acknowledged) _before_ the new FM/FCS is released.

[niru27]

Any news on this? It's been a ~year since the new FCS brought this issue which makes defending in BVR, say by performing a Split-S, almost impossible

[DummyCatz]

On 2/20/2025 at 2:19 AM, niru27 said:

Any news on this? It's been a ~year since the new FCS brought this issue which makes defending in BVR, say by performing a Split-S, almost impossible

Depends on the progress of the mentioned FM/FCS refactoring.

[niru27]

Speed brake issue got fixed in today's patch, but this is still pending

[NineLine]

Please test and let us know. Thanks. 

[niru27]

On 3/20/2025 at 4:01 AM, NineLine said:

Please test and let us know. Thanks.

Been a while since I flew so can't say if you made any changes in the latest patch, but I just tested, and the pitching oscillation due to unstable G still occurs. HUD recording attached for reference

• First, watch the clip and just look at the Controls overlay to verify I'm holding a constant backstick pressure
• Then, rewatch the clip and just look at the G values. Playing in slo-mo will help

You'll notice G oscillates up and down, first it maxes out at 7.8, unloads to 5.6, and then keeps going up and down repeatedly, before stabilizing at 6.5

7.8 > 5.6 > 7.0 > 6.1 > 6.5

The above unstable/constantly varying G is what is making the aircraft behave erratically.

If this is considered normal, why aren't other jets doing the same?

Just fly F18 and, say F16 and perform a Split-S back to back at the same altitude/speed, and you'll realize that this is just weird behaviour.

[BIGNEWY]

Refinements to the flight model and flight control system are in progress. Please add a track replay from your test.

thank you