This is either genius or honest error.
At the speeds of our foamies, we can treat air as an Incompressible fluid. As long as he is not constricting the exhaust, he should not lose too much thrust. The intake would be the more important area to tune. If we take what he has designed there, “minus” the trim rings, we can see some reason to having the pass through area from the square duct surrounding the round EDF. This would in effect allow the high pressure area at the corners pass through past the round EDF housing.
On the other hand, the trim ring drawn in the 3D model would not help in this situation though as the radius of the lip would try to reverse the air passing by the housing 180*.
You would be better off either leaving the intake lip ring off and allowing the air to pass through the square duct, or walling off the square duct to create the high pressure area to help feed the EDF lip ring, which would boost air velocity to help feed the tips of the fan blades.
I think in this situation you would be better off leaving the lip ring off. If you look at Mid7night’s F-5 EDF duct work you will see the same design reasoning.
That said, fluid mechanics is a very complicated animal. Trial and error is really the best way to tune aero flow and thrust. Even then, at these speeds and displacements, we are splitting hairs.
In any event, this is truly a work of art unrauv. I can not wait to see the finished product.
Edit: Disconnect between brain and fingers.
NOW I'M GONNA HAVE TO GET ANOTHER EDF AND ANOTHER BATTERY
