I've been noticing a lot of multi-rotors (mostly quads) that have their motors inverted, so that they are pushing rather than pulling. I can see that this would eliminate the prop-wash across the frame, etc., but has there been any actual studies showing this to be a real advantage?
Is the air intake across the frame and motors not as significant as it is when pushed across them?
Other concerns would be whether the motors would stay as cool, and whether the bearings (which were likely designed for pulling configuration) might wear out sooner.

Ralph