XPMorten said:
In other words, if you use a lookup table and want to hit book values
at all times, you will need 100.000 sets of data since WEIGHT changes constantly, also in cruise.
If you do the EXACT same flight, only with a small change in
Takeoff weight, you will need another 100.000 sets.
You have completely misunderstood how lookup tables work. There are no tables of performance versus weight, or anything else. What you have is this:
For each aero coefficient, there will be a lookup (or function) table. This is analogous to the data you enter for the aerofoil in X-Plane. On an FFS this might be two or three dimensional (say a function of AOA, Mach and Sideslip). In MSFS they are all one dimensional, e.g. CL v AOA. Some may actually be linear equations for simplicity. So MSFS will compute the lift coefficient for the current AOA. Other lift effects are added (due to flap, gear, spoilers, etc) then CL is converted to Lift by multiplying by (0.5*rho*V^2*S), yes MSFS knows about this too! The same applies to all the other coefficients in other axes (I doubt MSFS considers sideforce, but it will have CD, CM, Cl and CN.
These forces and moments are integrated in the EOM (which is, I concede, simplified compared to X-Plane, and
the only real difference between the two sims). The effect of changing weight (and anything else) will be automatically considered by this model, in
exactly the same way as X-Plane.
There are some global tuning factors in the
aircraft.cfg file, which also sets values like stall speed, Mmo, etc. Note, the aircraft.cfg file does not set aerodynamic stall speed, the value is just to trigger the stall warning message. Tuning factors make the designers job easier, but don't detract from the validity of the model.
An FFS has CL, for example, broken down into many contributing functions, whereas MSFS will probably only have the basic lift curve slope, but that is just like X-Plane too.
Even X-Plane only considers one dimensional functions for its aerofoils (CL, CD and CM versus AOA). You can have two functions (one for high Reynolds No, one for low) with linear interpolation in between but that is still quite crude, especially for high speed aircraft.
Reading the X-Plane forums I came across references to MSFS using a "behavioural" model, which ties in with your thoughts on how lookup tables work. It is an entirely false description of how the MSFS aero model works.