One that comes to mind is Warbirds, although not free you can sign up for a free months trial to try it out,
Other than that i cant really think of any good ones, there seems to be a general lack of good combat flight games.
Samsung Galaxy S9 review
Wacom Cintiq Pro 24 and 32 review – hands-on
When is the next Apple event?
Qu’est-ce qu’Amazon Prime ?