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abrams_tank

MSFS has the most advanced flight model?

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Over in the MSFS forums, there is a very interesting thread about the MSFS flight model.  Some posters in that thread, who seem to have a knowledge of the physics/mathematics with aerodynamics, are saying that MSFS actually has a better flight model than X-Plane.  The thread in the MSFS forums is here.

So I am not an aeronautical engineer and I do not know the details about the physics/mathematics involved for aerodynamics.  But I saw some interesting comments in that thread and maybe people here that know the physics/mathematics with aerodynamics can comment further.  Some of those comments are:

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If you really try to follow the theory behind both BET (X-Plane) and MSFS’ aerodynamics model, you’ll soon find that they’re nearly one and the same. They’re both geometry-based, real-time models for calculating the forces and moments on an airframe. So, then the discussion becomes - what is it about BET that would draw more users to MSFS?

There are obvious advantages of using these geometry-based models over table lookups, but also drawbacks. Austin himself has devised countless kludges over the years to account for those deficits.

In my opinion, I think the MSFS model is off to a great start. For one, it does a spatially finer-grained force calculation than X-Plane does. The MSFS model is discretized into something like 600 elements, where as the BET model uses only tens. I just think we’ve all seen that it could benefit from the years of bandaid fixes X-Plane has gone through.

https://forums.flightsimulator.com/t/developing-a-blade-element-theory/407516/3

Quote

Regarding BET, MSFS’s flight model is light years ahead of X-Plane’s, and is in fact quite similar in basis, but allows many, many more surfaces to be involved in the calculations of lift and drag than X-plane does (I forget off the top of my head, over 1,000 vs 10, something like that). Unfortunately, the X-plane comparisons have been removed, but if you can find an old copy of the SDK and the description of the Flight Model, you can see what I mean.

And, yes, Asobo is not done yet with the flight model. There’s a huge amount of extensibility built into it and there is a long list of features they have yet to implement. And to those who claim Asobo isn’t interested in Aviation, have you watched any of the developer Q&A’s? They’re all pilots and at least Jorg (and Seb?) I believe owns a plane.

https://forums.flightsimulator.com/t/developing-a-blade-element-theory/407516/15

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This has needed to be said. X-Plane did not invent blade element theory. In fact, their application of BET is nothing but a glorified strip theory method. There’s nothing wrong with that, but that is what it is.

I think it’s funny when people say that this blade element method is inherently superior to the MSFS aerodynamics model. If you take away all of the kludges, it’s not that sophisticated. Literally, X-Plane takes 10-20 slice cuts of wing and stabilizer surfaces and calculates the forces on each slice. Each slice is a 2D airfoil. Sounds great, especially for long slender wings with large aspect ratio. I don’t know how they are handling crossflow effects, because each 2D slice is totally independent of it’s neighbors, but there’s probably some kludge there.

MSFS, on the other hand, is actually discretizing a surface representation of the airframe into almost 1000 elements, and solves for the aerodynamic force on each element. This is what’s called panel or boundary element methods. Less sophisticated than full-on Navier-Stokes calculations, but far more precise than a strip theory method. Wonder how the big aerospace manufacturers designed airliners back in the day without the CFD we have today? Panel codes. Of course, back then, solving for the forces on 1000 elements probably took them days. Now, we can do it in mere seconds.

https://forums.flightsimulator.com/t/developing-a-blade-element-theory/407516/19


Finally, it looks like the details of the MSFS flight model are available now at: https://docs.flightsimulator.com/html/index.htm#t=Additional_Information%2FFlight_Model_Physics.htm&rhsearch=flight model&ux=search


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Theoreticals aside I'd say the proof of the pudding is in the eating...if MSFS FM is so good why do the planes fly so bad?

Maybe one day....

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All I know is when I try a simulator, I compare how it feels to how it feels when I fly an aircraft in real life.  X Plane never made me feel like I was flying a real aircraft. MSFS 2020, with the aircraft I have tried, the C 172, Mooney, JF Arrow and Seminole twin, feel to me just like what I feel flying a real aircraft. 

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I know this is going to ruffle some feathers...but It simply does not matter.

I have 2 current students that started as simmers first. They started by touting the merits of another sim with a “superior” flight model. After the first few lessons by the time we started working on landings, both realized that the sim was nothing life real life. I’m not saying that sims are not valuable or fun, but I wouldn’t get all worked up about A vs B flight model. Truth is any of the current sims can work well enough. 

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Chris

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Posted (edited)
3 minutes ago, keithb77 said:

Theoreticals aside I'd say the proof of the pudding is in the eating...if MSFS FM is so good why do the planes fly so bad?

Maybe one day....

But that's not what I have read though.  Some real life Cessna 172 and Cessna 152 pilots have already commented that the Cessna 172 and Cessna 152 fly very well in MSFS.  And Bobsk8, who is a real life pilot, is saying the C172, Mooney, and JF Arrow fly much better in MSFS than X-Plane, based on his experience piloting those planes in real life.

Edited by abrams_tank
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Posted (edited)

Bait thread beginning of the work week lets not lure in the outsiders.

Edited by jbdbow1970
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Posted (edited)

Sure this thread will go ballistic, but I'd agree with snglecoil, I'm a R/L glider-pilot-in-training and no sim FEELS like a real aircraft, there are some similarities and some big divergences, and each sim has different ones.
I think right now there are better X-plane aircraft but maybe there will in future be better MSFS aircraft, the 152 being the best I've tried so far.

For sure MSFS looks best from the cockpit, and that's a big part of it feeling right.

 

Edited by keithb77
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The basic engine is largely irrelevant, as long as it's sufficiently flexible, in that the performance is entirely down to the people who code the flight dynamics.

I know that certain sims like to push their flight dynamics models, which of course means that everyone who spends 17 seconds reading about it becomes an expert on aerodynamics and can say with confidence that theirs is the best. In reality I expect that those people wouldn't know the lift formula if it slapped them in the face.

Then you have the number jockeys, who like to complain if the performance in the sim isn't within a gnats fart of the POH, when in reality you'd be lucky to get within a country mile of them in a beat up old Piper Warrior with flaking paint.

So in summary, don't get worked up about it. The only times active airflow predictions come into real play are during out-of-envelope excursions, and I would hazard a guess that there doesn't exist a simulator which can accurately model the chaos-based physics of such events. Even the finest airliner simulators come with the caveat that 'beyond the envelope this sim is basically guesswork.'

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34 minutes ago, Bobsk8 said:

All I know is when I try a simulator, I compare how it feels to how it feels when I fly an aircraft in real life.  X Plane never made me feel like I was flying a real aircraft. MSFS 2020, with the aircraft I have tried, the C 172, Mooney, JF Arrow and Seminole twin, feel to me just like what I feel flying a real aircraft. 

That's interesting. I have always nearly bought the propaganda about X-Planes flight model but never to the point where I've believed it entirely. Mainly because there are two to choose from and if there are two both cannot be correct?

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I remember early on there was a thread created on the official forum by real pilots begging Asobo not to pay too close attention to the complaints of the armchair simmers where the flight model is concerned. Personally, (and I say this as someone who does not have an hour of real world flight time) MSFS does indeed seem to have the best platform for getting things the closest to real world parameters. Tweaks definitely have to be made and they need to fix ground handling asap but they're off to a great start.

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12 minutes ago, jarmstro said:

That's interesting. I have always nearly bought the propaganda about X-Planes flight model

I bought the propaganda about the X-Plane flight model too.  A lot of the X-Plane advocates keep repeating it over and over again.  But that thread from the MSFS forums really shed some light for me on the flight model between X-Plane and MSFS. And some of those commenters in that thread seem to be coming from an aerospace engineering background.  The general idea that I got from that thread was that the MSFS flight model has way more potential than X-Plane's flight model, but that MSFS needs to "tweak" the flight model for it to realize its full potential (ie. after some time when the flight model has been "tweaked," MSFS's flight model will be far superior to X-Plane's flight model).


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16 minutes ago, jarmstro said:

That's interesting. I have always nearly bought the propaganda about X-Planes flight model but never to the point where I've believed it entirely. Mainly because there are two to choose from and if there are two both cannot be correct?

You are operating under the premise the one or the other is “correct”.  What if neither are “correct”? 😉

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Chris

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59 minutes ago, keithb77 said:

.if MSFS FM is so good why do the planes fly so bad?

Maybe one day....

How do the WT CJ4 or the Longitude "fly bad"?

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Posted (edited)
14 minutes ago, Ricardo41 said:

How do the WT CJ4 or the Longitude "fly bad"?

He may be referring to something I've noticed. Planes in X-Plane are very very easy to fly. Flying is silky smooth. Unrealistically so I think from the limited experience I have with VFR flight as a passenger in my daughter in laws small family plane.

Edited by jarmstro

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1 hour ago, abrams_tank said:

Over in the MSFS forums, there is a very interesting thread about the MSFS flight model.  Some posters in that thread, who seem to have a knowledge of the physics/mathematics with aerodynamics, are saying that MSFS actually has a better flight model than X-Plane.  The thread in the MSFS forums is here.

Oh, God... This won't end well.....

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