Looks like this has been asked for couple years back, but here goes:
Currently, you check the option for tracers in the flight options of the clipboard. Your decision effects all planes that you up, wether its a yak, spit, b-17, or bf-110. One time i turned off tracers to dogfight in a p38. I later upped a b-17 to bomb and found it very difficult to defend myself without tracers. Might be nice to be able to customize each aircraft to use or not to use tracers individually. This could be done in the hangar, next to the option to customize your gunsights for a vehicle position.
Also a minor note, I noticed that the drones on bombers still fire tracers even if the "no tracers" option is checked and the lead bomber is not firing tracers. Looks like a bug, I'll make a separate post if it hasn't already been discussed or was coded on purpose.