MSFS flight models, aerodynamics, etc

Posting this on a separate thread, at the urging of some :slight_smile: … some stuff I feel would be good for everyone to be aware of given how much this topic comes up, and to counter some misconceptions out there still about MSFS and flight dynamics, etc. Also how when it comes to evaluating flight dynamics in MSFS that it’s important to separate the core aerodynamics engine vs flight models per aircraft, and default aircraft vs add-ons, etc.

So firstly the default aircraft in MSFS… Yes they are nothing home to write about, and maybe the C172 is Asobo’s best out of the lot. But the with coming November release and inclusion of properly modeled aircraft like the iniBuilds A310 and Milviz Beaver, MSFS will finally have default aircraft with great flight models. iniBuilds themselves have said: Discord : “Just to be fully clear, our flight model in MSFS is on par to XP. So those still wanting to negate MSFS as a viable sim solution based on those reasons - don’t speak too soon.

Secondly, it’s important to keep reiterating that there is no “one flight model” in a sim… it’s the sim’s core aerodynamics/physics engine which is then used to implement flight models per aircraft. Up until May 2022, all MSFS had were the default aircraft whose flight models were poorly and sparsely implemented. The core MSFS aerodynamics engine is very capable and what’s important are properly implemented aircraft… Enter May 2022, the flood of high fidelity aircraft with great flight dynamics (i.e. Fenix A320, PMDG 737, Milviz C310, Maddog MD80, Bae 146, Sting S4, etc) who all implement their flight models properly on top of the core MSFS aerodynamics engine, and some which have started to take advantage of the latest advancements to the aerodynamics engine like prop physics, CFD, softbody physics, etc. These birds all have great flight dynamics/handling not just observed by us simmers who’ve used all sim including XP, but also those who’re IRL pilots of these (for example, the likes of V1 Simulations, Into the Blue Simulations, 320 Sim Pilot, Flightdeck2Sim, etc who’re real world airbus and boeing pilots have had a lot of praise for both the depth of systems simulation as well flight dynamics of the Fenix A320 and PMDG 737… The Milviz C310 too has been lauded for IRL Cessna pilots)

Some good insights below by Matt Nischan of Working Title on flights models in MSFS and XP from his other forum posts (and this was before the prop physics and CFD enhancements came in SU8/SU9):

"There’s no conclusive observation that can be made by looking at one specific aircraft flight model configuration and then applying that conclusion to the entire flight simulation. How well a particular aircraft meets book values is entirely dependent on how well the flight model author adjusted the values to make the book values possible.

This is exactly the same in both MSFS and X-Plane. X-Plane only uses geometry to the same extent MSFS does, for the most part. All the complex study level flight models developed in XP heavily use datarefs to adjust various tables and scalars to modulate the output of the simulation, because all simulations are imperfect.

If the flight model designer has not input the correct parameters into the model, then you get a ■■■■■■ simulation, both in MSFS and XP. It’s why the default 172 in XP flies like it has no idea what longitudinal stability is, while payware offerings are much better: that doesn’t mean XPs flight model overall is garbage, just that the configuration of it may be for a given airplane. Similarly, taking the default 787 which doesn’t match book and claiming it means something about the core of the MSFS flight engine is just misguided.

In the right hands, the MSFS modern engine is going to produce some seriously accurate aircraft. How do I know that? Because our Working Title CJ4 does actually hit those book values at all regimes, with correct N1s, fuel flow, climb rates, over various altitudes and ambient pressures. Not only that but we have stall speeds within a knot of two of book, proper approach angles, correct bank rates, etc.

Is the MSFS simulation completely perfect and without limitations or quirks? No, but neither is XPs, by a long shot. These strange questions and tests are apples and parsnips."

"Additionally, MSFS categorically does not use Blade Element Theory. Blade element theory is the idea that you can slice an airfoil up into cross sections, evaluate those cross sections, and then come up with a single lift and drag component for each cross section. XP does this slicing across the defined lifting surfaces to generate a limited number of lift points. It is relatively coarse and doesn’t generate different values across each individual surface cross-section, but nonetheless it is used to great effect and the work done with it is quite good, as I’ve said before.

MSFS also starts with a base geometrically defined lifting surface, but then goes a completely different direction and discretizes the lifting surface into a large number (comparatively) of grid samples. Each individual grid sample receives its own airflow simulation that gets input from the airflow model in true 3d space: i.e. the atmospheric model is also 3d and thus the air itself is not a just a single scalar contribution but instead a varying 3d contribution across each grid sample where the atmospheric model and grid intersect. This means that each grid sample on any lifting surface contributes its forces individually and is also affected by a 3d atmospheric model individually.

Whether or not one believes the current aircraft flight model configurations use this well or whether enough parameters are exposed, the base grid sampling of the MSFS flight model is of a much higher resolution and the atmospheric contribution in 3d is a consumer sim first (to my knowledge, anyway). It also has the benefit of generating different lift values across the surface from front to back, which can be critical value differences at the flight envelope edges."

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I don’t think so, not after this new CFD model causing the stalls / spins straight out of GTA V. What do you think about swept wing aircraft in MSFS? They all have the center of pressure far in front of the CG with a up-force on the horizontal stabilizer in flight, in real life this would cause longitudinal instability, not in MSFS because the CP moves in the opposite direction with a change in AOA. Someone once showed in dev mode that as soon as you introduce sweep angles everything starts to work in reverse. That must be something with the core engine?

Well, out of all the current default aircraft without any mods, the C172 is still perhaps the most realistic I feel. I would definitely not call it GTA V level however lol. Maybe at the edge of the flight dynamics envelope it’s not as good or something was not reconfigured properly when they adapted it for CFD.

And yes in terms of being able to fully configure delta-wing aircraft, the core platform needs some improvements.

The only area I feel where improvements are definitely needed is ground handling/physics, but Asobo have also acknowledged this as a focus area starting with SU10 and then beyond:

Live Dev Q&A - March 2nd, 2022, note Seb’s lengthy answer to the question “Any update on the revamped ground physics handling/friction?
Excerpt: “For example, a wheel is currently simulated as a single point. So, a wheel can resist movement or rolling or sliding when you brake. It does not resist rotation. A wheel can rotate [with a rudder or tiller] without resistance. If you’re in your car and you’re parked, and you turn the steering wheel, if you don’t have power steering, it’s not easy to turn the tire because it’s not a point: It’s a flat surface. It’s a patch on the ground of rubber that you’re moving. The new simulation is going to allow this. This helps with stability when you’re taking off. Currently, the plane is just a tripod of points, and as soon as the nose is up, you feel that it’s already twisting because the wheels are not simulated as patches of rubber. They do not resist rotation enough. These kinds of changes are going to make the moments of takeoff a lot more precise and realistic. Later this year.

Specific ground physics improvements coming in SU10+: Twitch

Yes indeed, I’m calling the stall / spin behavior GTA V the rest of the flight envelope is not so bad (not great either). Not necessarily delta wing, every form of swept wing works completely opposite from real world aerodynamics. Ground handling is indeed awful currently.

Another problem is the inability to pull any aircraft into an accelerated stall as flight control surface deflection is depending on speed. You can only see this in the dev mode. At high speed the aircraft performs loop after loop instead of pulling the wings of or stalling (below Va speed). When performing a stall during steep turn you simply run out of elevator authority and the aircraft will start descent instead of stalling while holding the stick full back.

Another problem is the inability to pull any aircraft into an accelerated stall as flight control surface deflection is depending on speed. You can only see this in the dev mode. At high speed the aircraft performs loop after loop instead of pulling the wings of or stalling (below Va speed). When performing a stall during steep turn you simply run out of elevator authority and the aircraft will start descent instead of stalling while holding the stick full back.

I presume once again you’re talking default GA aircraft here. There are some good GA add-ons like the Milviz C310, Sting S4, FSW C414 that are really good in their stall modelling. The gold standard of GA aircraft simulations is A2A, and they will be releasing their Piper Comanche for MSFS soon and I expect that one to have the most realistic of flight models amongst all payware/freeware GA birds.

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The problem is not the stall behavior, as I understand this is not something which can be modded, pulling the stick full back at high speed will not result in max elevator (or any other control surface) deflection. This is alright to some degree to simulate increase in stick force at high speed to compensate for the missing stick force and g-loading but it’s quite overdone. Not being able to stall an aircraft during turn or being able to pull the stick full back without consequences is wrong. Will try out some 3rd party aircraft.

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What I very much wish to see is where we can deflect the aileron in to the wind without tipping over. In Xplane 11 this is properly simulated and I like that because it is the correct thing to do.

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I have noticed that the Milviz C310R works rather well in this regard. Better than other GA.

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Agreed. The Milviz C310 is probably the best overall GA add-on aircraft for MSFS at the moment, and especially when it comes to flight dynamics (it also takes advantage of the new prop physics and CFD capabilities). Hopefully their Beaver that’ll be included in the 40th anniv edition will be as deeply modeled.

As long as the RL pilots amongst the simming community aren’t able to agree upon whether the flight model is realistic or not, I tend to take many comments about the flight model with some grains of salt.
Some say that they feel the weight of the plane, some say it’s twitchy. Some say it floats, some say it’s realistic ground effect. Some say the plane, given the right aoa has a correct left tendency, some say too little right rudder is needed, or too much.
I really don’t know what to believe. That’s why I decided to train for the license myself, so that I will be able to tell you all, from a first hand, educated perspective, if it’s realistic or not.
:face_with_hand_over_mouth:

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I think like this.

If the devs continue make the simulator more realistic than it is now in the future i’m fine. If another dev create another more realistic simulator i usually use that too. I buy the most addons for the simulator that i find gets the most updates in realism and what i personally find more realistic. As it is now we have not much to choose. I think that will change soon though. And competition is good :slight_smile: I think many that uses this sim likes it because we can look at the rendered world. To me it’s more important to have the actaul flight environment realistic. If we can feel the varied atmosphere we fly in and at the same time have an as accurate flightmodel as possible i’m really happy. The scenery is only a bonus for me because that gets static and boring. The atmosphere is always changing and never gets static in the real world. I think that the atmosphere always is varied/unpredictable makes pilots continue to fly even if they fly the same route all the time.

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I’m not sure if the SDKs need improvement to make the flight models easier to implement, but the developers of the airplanes you mentioned really put in a tremendous effort to detail. There is something about the Sting that gives me a greater sense of flying than just about any other airplane in the sim.

I’m not sure all the developers put that level of effort in or if it’s even financially viable to do so.

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Unfortunately it’s very subjective when it comes to anything other than comparing performance figures to a POH. I think everyone agrees the flight model of all default planes are not very realistic. They don’t respond “fluid” enough, everything is just twitchy for lack of a better word to describe it.

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I liked this early comment from @SuperSixBravo:

After doing some deeper checking of things and asking a few friends and co workers who fly jets to GA, I have come to this conclusion.

The flight model is actually very good, The planes are the problem. The actual modelling of the planes is not taking advantage of the flight model. Its almost like the planes are using 50% of what the sim can potentially do and some of the flight models are seem to be baked as in “Just get it to fly” we will fix how it fly’s later on. Again the systems in most cases are basic, but is not to do with the Flight model, but obviously will be influenced by it once fixed.

So this means that there obviously are a lot of factors into play which makes pointing toward the quality, or lack of, the flight model problematic. To name a few:

  • the modeling of the plane
  • the actual conditions
  • the controller settings
  • mass and balance considerations

What you are saying about flying in standard conditions and comparing performance to the POH seems indeed the best way to objectively test this. We should standardize on controller settings also, I would think.

But, if the planes don’t exploit all possibilities that the flight model exposes, we are left with half baked products. This means that we really can’t know if the flight model is realistic or not, until some vendor sells us a study level c172 that blows the default out of the air. Then we’ll know what the flight model is capable of. I would gladly slap €40-€50 on the counter for such a plane.

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That could be the case, I don’t own the MilViz C310 or PMDG 737 so I don’t know how their flight model is. The default aircraft are quite bad, that is all I can say. The C172 has stall / spin behavior similar to GTA V after the CFD implementation. Often displaying forces in dev mode also doesn’t make a ton of sense from an aerodynamics perspective, 1/3 of the wing producing negative lift in cruise on the C172 for example, on swept wing aircraft the CP is far in front of the CG with an up-force on the horizontal stabilizer, I don’t know if those are problems with the flight model of that particular aircraft or core engine. In the latter case I suspect its the core engine. Also maximum control surface deflection is limited by speed, when applying maximum control input at high speed the control surface won’t go to max deflection. This was an attempt I believe to simulate increase in stick force and g-load, not a bad idea but its overdone to the point you can’t pull any aircraft into an accelerated stall and the aircraft just loops instead of stalling when keeping the stick full back, not sure how 3rd party planes handle this scenario. And ground handling is just off, doesn’t matter if its a third party plane or not.

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It should also be unnecessary to take sensitivity down to -50% to make it flyable, in real world the control surface deflection follows the control column 1:1, why do we have to reduce sensitivity in MSFS to make it more realistic? In general I think everything is too quick reacting, not enough inertia going down the flight path, flight controls are too effective. I think that is what destroys the more fluid and sometimes sluggish feeling of flying a real aircraft. Again talking about default aircraft as a disclaimer.

What yoke are you using? I’ve never felt compelled to touch any of the sensitivity settings for my Honeycomb yoke, and both the 152 and the 172 feel pretty smooth to me.

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I’m using a stick, unflyable is maybe an exaggeration but from what I read on the forum a lot of people reduce sensitivity levels. Does the MSFS C172 feel as smooth for you as the X-plane C172? Somehow X-plane has managed to capture that feeling of flying an aircraft very well. Its hard to explain but something feels off on MSFS default aircraft, its too responsive, maybe its also the longitudinal stability which is off, lack of inertia. I don’t know. Its far off anyway, especially the stall / spin behavior since CFD implementation.

Actually a fair point. Will certainly test this soon and report back :grinning:. Just out of curiosity.
PS my last two flights with the other sim resulted in ctd 2 mins into the flight :wink:. So it can happen there too.

I tried flying the 172 the other day. I hadn’t tried it in months. In a power on stall, even with full left rudder the right wing dropped. :flushed: