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MSFS flight model

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10 hours ago, blingthinger said:

I wonder. How much of this is due to a wide range of joystick equipment and sensitivity curve settings? Would this play into the pitch oscillations as well?

This was much discussed in the early days of release. My view is that unless you have a very short throw on a small joystick, a straight, linear control profile should suffice and if you need a bunch of extreme curves in input profiles that is indicative of a poor flight model. If you can land a typical sim tail dragger by just a small back movement rather than having the stick way back in your lap, then the flight model is too sensitive in pitch, at least at slow speed.

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1 hour ago, robert young said:

This was much discussed in the early days of release. My view is that unless you have a very short throw on a small joystick, a straight, linear control profile should suffice and if you need a bunch of extreme curves in input profiles that is indicative of a poor flight model.

My words. In a real plane you don't have sensitivity curves. The only reason that would make sense for such (in sim) would be a stick with small movement ranges. Otherwise 1 cm on the stick should move the surface the same amount, no matter how much the stick is deflected. In other words: A linear curve is the most realistic.

If you have to tune it down a lot, it is - as you said - an indication of some shortcomings in the flight model.


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6 hours ago, mrueedi said:

spacer.png

Red is the curve, which FSX would have computed, orange is the curve computed by the 640 surface model alone, and green is the curve of the 640 surface model, scaled by the normalization coefficients to match the dimension needed met flight performance requirements.

Ahh, thank you very very much for the plot. I have some questions on this particular item. I'm looking at the orange line on the right half of the image where it goes vertical for a bit.

Just before the curve goes vertical, the pilot does something: the control column gets moved, or a wing enters a cloud, or the spoilers are deployed: some sort of abrupt step change in flight condition. 

The distance that the curve travels between where the curve suddenly starts going up, and where it then starts going down (amplitude of oscillation), might be considered the 'dynamic response' of the airframe.

The force elements are saying that this distance should be the orange line. The distance in the green line is shorter. There is less dynamic response in the green line. If the red curve (FSX) just happened to be above orange, that distance would get bigger. That's how scale factors work.

Does this mean the force elements are not generating realistic movement in the first place? IF they ARE, then the green curve is no longer realistic. The dynamic response has been muted. Yes, it does get more bouncy, but it's not entirely accurate. IF they are NOT realistic...I mean....you can finish that sentence.

Edited by blingthinger

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1 hour ago, blingthinger said:

Ahh, thank you very very much for the plot. I have some questions on this particular item. I'm looking at the orange line on the right half of the image where it goes vertical for a bit.

Now we are on the same page!

1 hour ago, blingthinger said:

The dynamic response has been muted.

..or amplified if the computed coefficents were > 1...

But you are correct, the amplitudes of the forces and moments are modulated. Whether that is a problem or not is not clear though, because we don't know, how accurate the 640 surface model out of the box already is. My diagram just illustrates the principle but could be way exaggerated. If typical normalization factors are 1.01, the impact to the flight dynamics could be ignored, if typical factors would be one magnitude of order higher (1.1), the error would still be small. So, as we don't know the typical dimension of this normalization, we can't draw any conclusion.

 

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46 minutes ago, mrueedi said:

Now we are on the same page!

So, as we don't know the typical dimension of this normalization, we can't draw any conclusion.

We always were on the same page. 

Absolutely. Sometimes the scale factors will be small. Sometimes imperceptible. But they will always be there. And in some situations will be big enough to feel and notice. Those are the dynamics that are always going to be missing. Until FSX is eliminated from the equations, of course.

Edited by blingthinger

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Wow this thread got intense and scientific!  Very interesting.

I used to care so much for a well modeled aircraft.  But how can one even say what is well modeled?  I'm sitting in my office chair with a 20 yr old Microsoft sidewinder stick.  It's nothing like when im sitting in the pilot seat of the small Beechcraft I fly irl.  The view is different, the sound is different, the feel is different, the flight controls are different.

At the end of the day I'd prefer a flight model to feel like I think it should - and that may be very different than someone else.

What I do care about still are numbers - POH/AFM.  I like when sim aircraft can hit the real numbers provided in the real documentation.  Only a handful of developers can do that AND provide that perfect feeling that the real aircraft would produce.  And it doesn't happen in one sim or another - it's only by the skill of the flight modelling expert.

I've yet to come across an aircraft that could handle a stiff crosswind landing as well as the Realair Legacy in P3D.  The SF260 in X plane 11 is probably the next best performing flight model in my opinion.

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32 minutes ago, blingthinger said:

Until FSX is eliminated from the equations, of course.

Yes, but why do that? FSX is not standing for FSX actually, but for the classical aerodynamics theory, which is easy and elegant to sepcify and tailor the flight performance. Addon devs are providing global aerodynamics coefficients and tables and the normalization ensures with a good accuracy, that the 640 surface model is matching with these.

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1 hour ago, mrueedi said:

Yes, but why do that?

Because in 30 years, it will be purely a CFD solution, no? Not even BET. Maybe they'll leave FSX in there for nostalgic reasons. To remember the mostly-good-old-days.


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I just finished watching a Youtube video where a pilot compared the MSFS 172 with the real thing, and he actually said that landing was pretty close, only takeoff wasn't realistic.

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1 hour ago, mrueedi said:

Yes, but why do that? FSX is not standing for FSX actually, but for the classical aerodynamics theory, which is easy and elegant to sepcify and tailor the flight performance. Addon devs are providing global aerodynamics coefficients and tables and the normalization ensures with a good accuracy, that the 640 surface model is matching with these.

That made about as much sense as Donald Trump on a bad day

 

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Seems like people are now saying just the take off, landing and ground handling feels poor. But Asobo has acknowledged and knows why that is 🙂 

Interesting times. 

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1 hour ago, mrueedi said:

the 640 surface model

By the way, has Asobo published any papers on this surface model + CFD in any aerospace journals or conferences of the AIAA or ASME? 


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5 hours ago, blingthinger said:

By the way, has Asobo published any papers on this surface model + CFD in any aerospace journals or conferences of the AIAA or ASME? 

Why should they, don’t they have more important things to do at the moment? Seb seems to be involved heavily with the flight model and the last thing I want Seb doing is wasting his time preparing an article for an aerospace journal over doing his actual job, which is fixing stuff and getting SU 10 out the door and preparing for try SU 11 beta,

Do you just make comments like this for argumentative purposes? I’m glad you’re not running MSFS because you would waste time on academic journals rather than address a lot of backlogged tasks that has much higher priority.

Edited by abrams_tank
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10 minutes ago, abrams_tank said:

Why should they, don’t they have more important things to do at the moment? Seb seems to be involved heavily with the flight model and the last thing I want Seb doing is wasting his time preparing an article for an aerospace journal over doing his actual job, which is fixing stuff and getting SU 10 out the door and preparing for try SU 11 beta,

Do you just make comments like this for argumentative purposes? I’m glad you’re not running MSFS because you would waste time on academic journals rather than address a lot of backlogged tasks that has much higher priority.

That was funny. Literally laughing here.

I do not mean to be argumentative. At all. It's a legitimate question in what has been an enlightening discussion about physics and technical fundamentals of aerodynamics. I ran a quick google scholar search before I made the comment and didn't find much. This just might mean Asobo has done something unique that could be recognized by the aerodynamic community (you know, where Boeing and Airbus engineers hang out). It would be a stamp of proof that they are pushing boundaries. That's all. But I suppose you're right in the end. Though I don't comprehend what you're worried about. Seb and Co. could take the time to write a paper and you wouldn't notice the lost time. Nor would their market share suffer a bit. Though obviously the folks in these halls would get upset.

In fact, while we're talking about journal papers and FSX, it's also worth noting that Bruce Artwick (you know, the genesis brain of what is now FSX and FS2020) hung out in that crowd. His flight simulator technically began life as a graduate research thesis funded by the US Navy when he was at University of Illinois: "A versatile computer-generated dynamic flight display". I found a copy just now but the URL is a US military site so probably won't work for all. Here's a screenshot:

 

guakBEu.png

11 FPS! With a RAIL!!!

The people who make this hobby possible at a fundamental level tend to worry about journals and such. I suppose one could say that for us nerds, it's the "cool" thing to do.

In any case, sorry to ruffle your feathers there...

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3 hours ago, abrams_tank said:

Do you just make comments like this for argumentative purposes? I’m glad you’re not running MSFS because you would waste time on academic journals rather than address a lot of backlogged tasks that has much higher priority.

Seems quite obvious IMHO. Remember Mr. Meyers flight model explanations in those videos? If I were an XP advocate, I would be rather careful when trying to point out who has better public FM documentation or who has to catch up in that regard. 

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