[Mat_Helm]

Because a model does not have the same weight, thrust, CG, aerodynamic forces involved. The model may look like an F-16 in dimensions and wing sweep, but does not have the same wing profile for supersonic flight, slats and flaps, fuel cell transfer system to maintain specific CG during flight, and other factors. Control surface dampening and computers prevent pilot induced oscillation (PIO) and require functioning AOA sensors along with the flight control computers. If you lose all the AOA sensors the plane is equally difficult to control. As the nose departs one direction and the pilot corrects it departs again in another direction and or over corrections by the pilot until he is chasing it to the point of complete departure. F/A-18 Hornets have the same problem if you lose the AOA sensors. The flight computers are continuously making small trim corrections to maintain 1G flight with hands of the stick. Even with pilot inputs to the controls the computers chose the best assortment of control surface deflections to accomplish the directional change input by the pilot as programmed and with design limitations for allowed positive and negative G forces. Flight test pilots take the test aircraft to departure limits in the design phase with unlimited and dangerous control and from subsequent tests software engineers create the code that than limits flight control movement to prevent loss of flight control. That is why flight testing is dangerous business and flown under strictly scripted maneuvers over time and testing departure limits beyond the wind tunnel and computer modeling.

[Sergio]

Thanks Mat, I had no idea that it all revolves around the relationship between CG and CL. Makes perfect sense once explained, but in my mind, the whole instability thing was much more complicated than that. I thought it was all structural design features and black magic.

Thanks for the very educational post.