I am trying to take an existing aircraft and change one of the engines as if it were a factory/manufacturers test bed for a very different engine.I don't see any way to do this but have limited experience with these kinds of changes and know almost nothing about the .air file. When I look at the .cfg for the Captain Sim 727-100 that has an unducted fan for engine #3 I see no change in any engine parameters. It looks to be like the visual model was changed but the engine dynamics remained as they were for the JT8D-15. Given that I'm guessing it is not possible to have two different engine types on the same AC.Can I do it?

I am trying to take an existing aircraft and change one of the engines as if it were a factory/manufacturers test bed for a very different engine.I don't see any way to do this but have limited experience with these kinds of changes and know almost nothing about the .air file. When I look at the .cfg for the Captain Sim 727-100 that has an unducted fan for engine #3 I see no change in any engine parameters. It looks to be like the visual model was changed but the engine dynamics remained as they were for the JT8D-15. Given that I'm guessing it is not possible to have two different engine types on the same AC.Can I do it?

I think this is fairly impossible. You can define the location of the engine, but not differentiate it from the other engines on the aircraft. Maybe someone can confirm this?

Only one engine type definition per aircraft. All engines in the model will be identical.