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ahsmatt7

Flight model improvements

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Hello, I’m looking for some of the more experienced folks in here to share some thoughts on this and start some discussion.

i have been fiddling with some settings within the flight_model.cfg filed for two airplanes as test beds. The tbm and the cj4.

before any changes I made, I noticed the tbm especially had a rubber band feel to it in the pitch axis. It was way to bouncy when hand flying. Not only that, the airplane would never level off with the AP engaged in a normal fashion. It would always porpoise it’s way up to altitude in the last few hundred feet.

I came across the cj4 flight model file and it has one line explanations of what each setting does in the aerodynamics section.

i saw that the line of “pitch_moment_pitch_damping” was commented as being the min pitch stability value and it mentioned deg/s.

i went back to the same value for the tbm and the value was extremely low...well into the negative values...somewhere around -300. I changed it to 0.0.

this helped drastically! I did the same with the yaw moment yaw damping and the squirrelly feeling on the ground is much more stable.

I downloaded the sdk and did some reading. Sadly there’s a ton of huge math equations and my math level isn’t nearly adequate enough to fully understand the settings in the flight model files.

if anyone of you who understand the math equations want to get together and figure this out, I think it would really help the community.

 

Also, any of you just want to test this out or and report back with your thoughts, let me know.

@robert young I’m tagging you on this because I’ve been following all your comments post release and after 1 month and 60 hours in the sim, I agree with all your comments on the flight model. Would love your feedback.

 

@cwburnett take a look at this. This thread and the discussions herein may help you down the road with the CJ4.

Edited by ahsmatt7
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FAA: ATP-ME

Matt kubanda

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Hi ahsmatt7. The pitch stability param is effective, but I am surprised setting it to zero helped. It should increase pitch stability with a greater negative value, not smaller. Are you sure your tweak did as you describe? A typical value for most default GA is around -250 or so. Increasing the negative value to up to three times or more (eg: -750) should increase pitch stability, not decrease it. You can see this clearly as the default airliners need lots of pitch stability and the default values are indeed a greater negative (eg -1102 or something similar).

But there is another way which is to increase the global pitch stability in the Flight_Tuning section. Typical GA values by default are 1.0 or less. You can quite easily bump these (positive this time) values up to 2.5 or beyond. The trick is to provide enough pitch stability that the elastic band bobbing up and down is largely eliminated but not so much that the nose doesn't gently drop when you reduce power, which is desirable.

There are many other parameters that affect pitch stability, one of them being inertia value in pitch at the top of the flight model cfg file, which IMO are set far, far too low (even though they look mathematically correct).

Other params include elevator delta settings, pitch moment vs aoa, lift vs aoa and a host of other params which I would advise being very careful about tweaking without a cast iron backup as things can get much worse rather than better (I know this to my own cost!). But the two main params mentioned above should address the worst of the bucking up and down. Hope this helps you.

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Robert Young - retired full time developer - see my Nexus Mod Page and my GitHub Mod page

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18 minutes ago, robert young said:

Hi ahsmatt7. The pitch stability param is effective, but I am surprised setting it to zero helped. It should increase pitch stability with a greater negative value, not smaller. Are you sure your tweak did as you describe? A typical value for most default GA is around -250 or so. Increasing the negative value to up to three times or more (eg: -750) should increase pitch stability, not decrease it. You can see this clearly as the default airliners need lots of pitch stability and the default values are indeed a greater negative (eg -1102 or something similar).

But there is another way which is to increase the global pitch stability in the Flight_Tuning section. Typical GA values by default are 1.0 or less. You can quite easily bump these (positive this time) values up to 2.5 or beyond. The trick is to provide enough pitch stability that the elastic band bobbing up and down is largely eliminated but not so much that the nose doesn't gently drop when you reduce power, which is desirable.

There are many other parameters that affect pitch stability, one of them being inertia value in pitch at the top of the flight model cfg file, which IMO are set far, far too low (even though they look mathematically correct).

Other params include elevator delta settings, pitch moment vs aoa, lift vs aoa and a host of other params which I would advise being very careful about tweaking without a cast iron backup as things can get much worse rather than better (I know this to my own cost!). But the two main params mentioned above should address the worst of the bucking up and down. Hope this helps you.

Interesting point about eh pitch moment pitch damping values. I’ll go the exact opposite (more negative value) and see what I come back with. 
 

woukd you say that the pitch stability values in the flight tuning section have a greater effect on fixing the rubber band bobbing effect? 
 

my next question for you or for anybody is why does the tbm autopilot now level off in a normal benign manner? I’m so curious.
 

I had someone else test the tbm with the 0.0 value and he said it was much more stable. The kicker was that he didn’t know that anything was actually changed. 
 

I’m extremely curious about these parameters as a whole. This is my first dive into these kinds of things.
 

Thanks for chiming in. Looking forward to more responses from you!

Edited by ahsmatt7

FAA: ATP-ME

Matt kubanda

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1 hour ago, ahsmatt7 said:

Hello, I’m looking for some of the more experienced folks in here to share some thoughts on this and start some discussion.

i have been fiddling with some settings within the flight_model.cfg filed for two airplanes as test beds. The tbm and the cj4.

Matt, sadly I'm not a flight model expert like Robert and others. I was hoping the MSFS SDK would shed more light on the parameters than the ESP/FSX/P3D SDK did, but alas, so far it doesn't - in fact they've introduced a whole new batch of parameters, at least on the engines.cfg side, without any mention at all in the SDK docs so far.

The ESP SDK is limited to one partial sentence at best describing each parameter, so I think most of the knowledge around flight models has been developed either behind the scenes with private help from the developers of those platforms, or learned through extensive experimentation by individuals and not well shared or documented. In either case, my efforts to understand have been limited by the general lack of documentation.

It has been my hope that the MSFS team would beef up the SDK docs over time and more completely articulate how each of the parameters interact and influence the in-sim flight experience, that way we could take a methodical approach to addressing the flight model problems with the CJ4 and other aircraft. Since we have plenty to do on the systems side, I'm content to give Asobo some time to get better SDK docs together.

The challenge is less about making the planes 'seem' better and more about trying to make them perform as true to life as possible, and right now the effort to make constant tweaks and then send our resident CJ4 pilot out to test them would just be too high - he and we don't have that kind of time to go messing with every variable in a scientifically rigorous way. It shouldn't be an unreasonable ask for the developers to simply lay out descriptively and mathematically how each of the hundreds of parameters in the various cfg files that influence aircraft behavior and systems work. After all, they must know what they do - they implemented them and then set values for the default aircraft. Seems like it would take just a couple days for them to document this and put it all out in the open, rather than perpetuating the status quo of a small and seemingly tight-lipped community of flight modeling gurus.

As far as I know, very little flight model tweaking has been done in an open-source, in the clear, manner - it's all held pretty closely by the developers that have figured this stuff out. Check out the FSDeveloper threads on the subject to get an idea of what I mean...

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Working Title MSFS Aircraft Mods | Working Title Discord

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1 hour ago, cwburnett said:

The challenge is less about making the planes 'seem' better and more about trying to make them perform as true to life as possible...

This is the crux of the matter for me. The airplanes don’t feel good at all in most cases....imo. I think the 172 and 152 are the best in my opinion that I’ve flown but as airplanes get bigger, they feel heavier, they are more stable and they pretty much stay where you put them.

that doesn’t necessarily happen in msfs. 
 

my point being that If these airplanes fly exactly by the aerodynamic numbers but the link between human hand and movement of the airplane in the sim is either unknown or nowhere near what said link would be between human and real airplane, we have to at least make the experience ‘feel’ right and comparatively close to what we would feel in the few airplane.

i just hope adobo and others shed light on how their world works in terms of wind and weather and interaction between the airmass and the airplane. That way we get true to life numbers and true to life feeling. 
 

I may be dreaming for that to happen lol

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FAA: ATP-ME

Matt kubanda

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3 hours ago, cwburnett said:

Matt, sadly I'm not a flight model expert like Robert and others. I was hoping the MSFS SDK would shed more light on the parameters than the ESP/FSX/P3D SDK did, but alas, so far it doesn't - in fact they've introduced a whole new batch of parameters, at least on the engines.cfg side, without any mention at all in the SDK docs so far.

If you need any input from me you are most welcome, assuming any aircraft you are tweaking is in the standard product as I do not have the premium versions.


Robert Young - retired full time developer - see my Nexus Mod Page and my GitHub Mod page

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24 minutes ago, robert young said:

If you need any input from me you are most welcome, assuming any aircraft you are tweaking is in the standard product as I do not have the premium versions.

I appreciate that Robert! When we get around to flight model stuff for the CJ4, I may just take you up on that! 👍


Working Title MSFS Aircraft Mods | Working Title Discord

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Have any of you found any combination of realism settings that allow for any depiction of adverse yaw in MSFS?

Or perhaps I am simply not noticing it, or not well-versed enough to know what I have or do not have?


Rhett

i7-8700k @ 5.0 ghz, 32 GB G.Skill TridentZ, 1080Ti, 32" BenQ, 4K res

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1 hour ago, Mace said:

Have any of you found any combination of realism settings that allow for any depiction of adverse yaw in MSFS?

Or perhaps I am simply not noticing it, or not well-versed enough to know what I have or do not have?

There is some adverse yaw and it is tweakable. You notice adverse yaw much more when coming out of a turn than going into one. If you set your view so the nose is dead on the horizon then do a turn to the left or right then unbank you will see the nose "drift" adversely to the direction of roll. Most GA aircraft have short wings so don't have that much adverse yaw, but it is there in FS2020. Of course gliding is a different matter entirely :)


Robert Young - retired full time developer - see my Nexus Mod Page and my GitHub Mod page

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