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MSFS MSFS2020 Flight Model

I know that it typically is but it doesn't appear to be how its done on some of the default aircraft. The dr.400 has a horizontal area of 0 in flight_model.cfg and there is even an error message that gets spit out in-game.

I'm wondering if this was intentional, ie how things were done in FSX, or if this is just some mistake. Given the error message I'm leaning towards the later.
In classical Flight Dynamics it always is.
To be more precise, it is the planform projection area (in case of wings, area of the shadow when sun is right above) including imaginary inner section that would exist if there were no fuselage.

But why is this area important if it serves no aerodynamic purpose on lift? Does the Simulation automatically exclude this from calculations? Just curious! Thanks
Indeed Alexis, as pointed out on various docs, including Yves:

"Example: If wing_area does not exist when the aircraft is loaded, MSFS will look for R1204_1 and will add the line and the value to aircraft.cfg. If R1204 is not present, wing_area is set to 0"

Also, from that doc we can see that all but main wing areas aren't used sin fs2004 / fsx, so probably also p3d and, it would be great to learn how it goes in MFS ...
But why is this area important if it serves no aerodynamic purpose on lift? Does the Simulation automatically exclude this from calculations? Just curious! Thanks

It is by convention, in aerodynamic calculations, to include the wing area "hidden" inside the fuselage.

In any case, there is a significant carryover of wing lift over the fuselage between the wings, and in addition the fuselage itself produces a lift force, so in the end the hidden wing area can be reasonably included in the "effective" wing area for calculations purposes.

For more precise calculations, there are empirical parameters to correct for the partial loss of lift due to fuselage, depending on the ratio of fuselage width over wing span, etc.

I'm talking about real aircraft design and calculations. In FSX, as has been said, the projected wing area is used, as is custom in aerodynamics engineering.
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