Most simulators fit into 2 categories. They are either a 'virtual wind tunnel' sim like Xplane that constantly calculates lift, drag etc. based on the geometry of a model, or they use look up tables, like MSFS.
The former is basically using a simple form of computational flow dynamics to calculate all the parameters. The latter relies on a big data file that tells the simulator what happens at different conditions.
For example, if modelling the lift from a wing, you'd need a file with angle of attack arguments from -180 to 180 degrees, mach number arguments from 0 to however high it needs to be, and finally a list of Cl values corresponding to all of those angle of attack and mach numbers.
Using this, the sim can, for example, realise the wing is at an angle of attack of 21 degrees and a mach number of 0.3 and look up the Cl. Unfortunately this only gives a 2 dimensional idea of how the wing is performing, so the sim will also need a way of numerically solving the 3D effect of a wing (using something like lifting line theory and horseshoe vortices).
These tables need to be present for everything from Cl, Cd, Cm etc. to the planform and geometry of lifting surfaces and fuselage.
To answer the stall question, as the angle of attack in the sim is increased, the data table Cl value increases until the point of separation, at which point it rapidly decreases. The subsequent loss of lift means the aircraft is heavier than the lift that it's producing and falls.
Ideally, the centre of mass would be above the wing, reducing the weight/lift moment couple as much as possible. behind the wing is a very bad idea as both the lift and the mass will combine as a couple and cause the nose to pitch up, and depending on elevator authority, may be uncontrollable. This is why aircraft have published CoG limits.
Hope that kind of makes sense/answers some questions
.mic
Last edited by Mictheslik; 24th Feb 2013 at 18:01.