How do you choose a side for your AC when making a mision.

In QMB you see in the right topcorner a button called "Allies" and when you click on it it says "Axis".
In FMB after selecting your aircraft you insert the point where you want to start your flight and in the objectwindow appear some more tabs. Select "Properties" and then you can choose Army Red (Allies) or Blue (Axis).

I just use multiplayer coop mode for any "Single Mission", leaving the AC player box unchecked. I can then play any AC for any side.

Thank you Guys!