According to the bf109 Emil manual (the real one from Messerschmitt) there should be a flap settings indicator on the left wing.
Like the picture below, although this one is obviously a right (starboard) wing
http://www.pbase.com/bertone61/image/79470175
Forgive me if it actually exists in the game on the right wing as I've only looked for it on the left and I'm in the office at the moment.