Developing a Blade Element Theory

Hi everyone I am new to these forums. I am an X-Plane fanboy I will admit that. The only thing that is holding me back from buying the new MSFS is there is no Blade Element Theory (BET) as I will refer it to. BET is not perfect but it gives a much more realistic and in-depth simulation than what this current MSFS has. I am suggesting that Microsoft have an optional BET mode that could help possibly bring more people from X-Plane to MSFS such as myself. MSFS is good eye candy but this would add another level to the current sim.



Forget it. This BET vs table based thing has been beaten to death over the years.
Both have their advantages and MSFS is kind of a mix between both, using the best of both worlds.

For how many hours have you used MSFS since the last update?


If you really try to follow the theory behind both BET 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.


You have the option to switch to a Legacy flight model in the sim.

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That’s not a useful option.
100% of the default aircraft and 99% of the add-ons require the flight model to be set to modern.

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Wasn’t aware of that. So why have the option then, is it for devs to do port overs?

I don’t know why this is a selectable option.
Switching to the legacy flight model is the main reason when people are experiencing problems with their aircraft.

AFAIK it was a MS requirement that old FSX flight models have to be somewhat compatible with the new sim.


MSFS would be absolutely sufficient in every way if everything they promised and they built into the simulator would work correctly.

Sure, it’s far from complete, but it would be a pretty solid foundation.

For simmers, it’s really more about getting stuff working correctly.

Aerodynamics alone just don’t cut it anymore. A realistic environment is just as important as a realistic flight model.


Is there any documented evidence to suggest that BET is for a fact better than the flight modeling MSFS uses? Or are you just falling to marketing hype?

I’m not defending the flight model in MSFS at all, it has its weird quirks, but to suggest that the all the efforts the devs at Asobo have made is just eye candy is a bit condescending IMO.


You are introducing a complicated technical topic … This is not for starters. So please explain what your critics is about. What BET model are you talking about… what would your BET model mean for a simulator (in terms of benefits ? accuracy ?)

Maybe you just read this topic of last night and conclude there is no propellor model at all ? You assume throttle setting T is just pulling MSFS planes forward with force a T*C or something ? I think that is not the case. You seem to know more about the internals of the MSFS propellor model, so please teach us. What are the shortcomings…


not needed, there is a test of a 172 in both xp and msfs, outcome same, xp is no longer
better. but if you like xp, well stay there, no problem. you can run both.

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where to find that test?

I have never flown a plane in XP that felt like a real aircraft to me. The Mooney and JF Arrow 3 in MSFS 2020 feel like a real aircraft, and I have about 600 hours RL piloting experience.


Dr400 pilot here. The plane in the game behaves just like you may expect it (maybe a bit slow on the roll speed, but I’m not even sure). I love the way you can keep its nose up during the flare, and this feeling that the plane will never touch the ground until you let him.


It was a contract requirement from Microsoft on Asobo. Asobo would not have included it given their druthers. After I pointed out their discussions and comparisons with X-Plane in the Flight Model Description in the SDK, they scrubbed a lot of interesting information out, which is what my comments are based on, but, basically, Microsoft required them by contract to include a mode which allowed FSX aircraft to act the same in MSFS as in FSX. Of course, we’ve all seen that this didn’t work out so well.

So, the answer is yes, I believe the intention was to support port-overs. Unfortunately, there’s more to an aircraft than its flight model, and the conversion of cockpit gauges etc has never worked well and was basically abandoned.

They should just remove the Legacy flight model option. It’s silly. Or move it to the developer mode if it’s really helpful. I have no idea why they continue to keep it facing regular users.

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.


@LogicUK6682 , @PZL104 , on that note, this is a Wishlist topic that might interest you:


Voted on that one already🙂

Thinking about it, removing this option might create another problem.

During the latest install a few of my aircraft did handle very strange.
To fix this issue I had to switch to Legacy and back to modern.


There seems to be a tendency amongst some XPlane users to present blade element theory as some sort of recent development in aerodynamics, offering prospects for accuracy in simulation that cannot be achieved through other means. This is however far from the case. Blade element theory dates back to the late nineteenth century, and has long been surpassed by more advanced techniques for modelling in fluid dynamics. Accordingly, while I think there is much to be said for the way XPlane uses this methodology in its flight modelling, the fact that another simulator uses other techniques need not indicate any deficiency at all. I have seen good flight modelling, and abysmal, in both XPlane and MSFS, and nothing I’ve seen so far suggests that one is inherently better suited to doing the job than the other. We should judge them both by the results, for individual aircraft, and not on the basis of marketing hype over specific technology. And perhaps it might be better to do so with an eye to the potential for future developments, since MSFS flight modelling is clearly still in a state of flux. XPlane took a long time to get to where it is today, and I see no reason to think that MSFS can’t also show the same potential for improvement.


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.


Great Post! Demystifying the glamour behind the BeT that people has been mentioning for years as the recipe for perfect aerodynamics…

What MSFS is doing is very advanced, I can see a LOT of potential. It’s just a matter of needed maturing process, correcting for the deviations from expected results that still exists, and it can be a really good end result!