I was looking at the aircraft.cfg file for the P-40 and noted that there are some smoke effects with
x,y,z parameters of 0,0,0 as well as some smoke effects placed further forward and to either side...those
would be the effects emitted from the exhaust stacks.
I don't have time right now as I'm about to go away from my SIM computer for a brief vacation but
my approach would be to set up a flight wjere these "flashes" are repeatable. save it, and then
go in an selectively "comment out" the various effect entries using a "//" at the beginning of the entry line.
I would first comment out the contrail entry to see if that is the effect that you are seeing causing the "flashes".
If not, go on to the smoke entries.
If it is the contrail fx, then it MAY be possible to reposition the emitters in the fx file itself to move
them further back.
If there is no determination or solution by the time I return and my schedule allows, I'll play
around with this at that time.
P.S. = be sure to back up, any files you intend to "tweak" before moving forward