Most add-ons aircraft, at least those build with AF99 and AF5, are using an MDL610 model file. CFS1 a/c are using CFS1 mdl files. The headers are different and the model variables for the gears and airscrew are different too. The few add-ons a/c that do show gears and props were "morphed" by implanting the visual code of an MDL610 file into a CFS1 model file.
This was, I think, first discussed by Corrado La Posta and implemented by a few designers. Very few add-ons do work this way.