Here's to you, the list of things to do to get the plane's secret END WAR, the XA-20 Razorback, without paying the dlc.
1) entary in the main menu of the game.
2) Go down the menu until you find downloadable content.
3) enter (this part will take some 'time because you will have groped more than 3-4 times to come, because it will restart the game without any reason).
4) Select the 'XA-20.
5) Download it.
6) restart the game.
Here's how to get the 'XA-20 Razorback, but will only be used online in the Cooperative Campaign.