Why don't aircraft owners put vortex generators on the top of their flaps to extend single flap lift creation past 40 degrees? Why don't ultralight/LSA aircraft owners put vortex generators (VGs) on the top of their flaps?
I understand that the maximum flap angle for a single lift creating flap is 40°, but 80° with a double flap, if each flap is rotated at 40°.
Why not put VGs on the top of a single flap to increase its maximum lift creation angle, and thus lift, to 45°, 50° or maybe even 60°, which would allow for a slower landing speed, hopefully in the 15-20mph range?
While Vg's might have been designed for wings, they are now used for elevators as well, which is very similar to an upside down wing and flap.  See picture below. Source: Zenith
Because the separation bubble, that vortex generators attenuate, occurs in front of the flaps.  There's no advantage to putting VGs that far back, on an ultralight or any other fixed wing aircraft.