Bjorn is correct. The old air files had a lot of data that is now specified in the aircraft.cfg. If you use an old air file with a section that is now in the aircraft.cfg the .cfg file takes priority. If you are missing essential data in the aircraft.cfg like wingspan for an airplane, the sim will insert a value.
The air files contain coefficients for engine data, lift, drag pitch yaw and sideforce. There is no absolute numeric data any more like wing span or CG.