Flight model physics

Hello all,

I have been working to improve the default 747-8 flight model and I have been reading the SDK and other resources in order to familiarise myself with the subject.

In the flight model physics SDK, it is indicated that the wing area is calculated as follows:

image

It looks to me that this is only half the wing area, or am I plain wrong and stupid?

To me, the correct formula would be:
image

In both cases, b is the wing span and c(x) is the chord in function of the lateral position x along the wing.

Thanks!

EDIT: better pictures for formulae and expression for the second formula changed to the double of the first formula

Wouldn’t that depend on whether by “wing” you mean both wings or just one of them? Most aircraft have two.

Well, I mean both wings as you say.

According to this link, the second formula I’ve put in the OP is the correct one for calculating the wing area.

Regarding the comment that was made by Yuudai5178, it would be weird to only consider half the wing in the analysis of the flight model physics.

I don’t know if these formulae are actually used by the MSFS, most probably not, but if some of them are wrong, then I assume that some of the weirdness of the flight model can be explained by the use of wrong formulae to model the aircraft behaviour.

Considering that all parts of the plane are processed individually it is not weird at all. Maybe try looking at some of their videos about flight mechanics.

If this is an attempt to explain “weirdness” then it is not useful at all. You don’t even explain what the “weirdness” is let along how that formula contributes to it.

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For starters, my point is not to convince you of anything and I appreciate your contribution to the discussion.

May I suggest you read the flight model physics page from the SDK?

This is what I’m referring to, not the videos that were made, that even though they are nice, they cannot be used when trying to analyse how the flight physics are calculated. By the way, what is explained in the videos is explained in that page too.

As for the weirdness I’m referring to, plenty of topics were made, and this one is a summary of all of them.
But to mention something here, I’ll say that straight wing planes are modelled correctly but airliners with swept wings and supercritical profile are far from what they should be with their CG being aft of their CP.

(Now I realize that below answer could already be found in that SDK-page… thx for the link)

Just a question, wondering… Isn’t this mathematical model involving a function c(x) not a bit too complicated for the MSFS2020-SDK ? Suppose you would change wing span in MSFS2020. It is shown as a parameter in the aircraft editor fillin form, along with other parameters. If you open the project while in the aircraft, then go drone, you can see geometry, but that consists only of straight lines, the green (change) dotted lines also. There is no curvature. Easy wing area formulas handling wings built up from straight lines can be found here at nasa.gov

Hi,

Thanks for your answer. I agree with you, and I’m still in the process of reading and trying to understand the physics aspect of the flight model.

I asked this question to the community because there are probably people with a better understanding that me on this subject, even though I’m working to improve this.

The point of the question is: even this formula is actually not used in this form in the sim, it was used to perform important calculations, such as the MAC, the AR, etc.

As it was also noted by other contributors in other topics, at the moment, the physics are off for planes with swept wings, i.e. airliners. I’m only trying to understand why. From my observations in the game, made using the default 747, the plane stall behaviour is wrong, the CP vs CG position is wrong, and the MAC position is wrong (the last two things are related to each other).

the flight model and geometry is not meant to be realistic or accurate. it’s still better than most sims out there maybe with exception of DCS. These values are arbitrary and are interpreted by the game’s engine however way the developers have coded them to. When i create an aircraft following the real world values the plane behaves nothing like the real thing and I often find myself changing values sometimes by up to 50%. For example in engine.cfg, increasing intake area of engine from 50 to 70sqft has a massive effect on drag. also the thrust is not linear, meaning 50kn of thrust is not 2x the power of a 25kn engine in the game, more like 2.5-3x. The biggest influence on drag in the flight model is the zero lift drag coefficient which i found setting anything above 0.024 creates huge amounts of drag. In terms of center gravity i usually need to give -9 to -15% of aft bias to make it realistic (given a 0 datum). Overall i find the default flight model to be too slippery, the center of gravity equations too front biased and engine modeling too tabular. it takes a lot of trial and error to get the plane just right and i often find myself sometimes resorting to flight tuning tables.