On this last flight of the test-bed before rework, the favorable downwash of ducted fans is clearly visible. Dust and debris are pushed away from the pilot, even while flying close to the ground.
The ducts prevent tip vortices from forming and isolate the fans from the external flow field. The latter quality permits unperturbed flight around obstacles and when transitioning indoors.
In contrast, the recirculating flow of open rotors has earned it a name, and the bane of pilots: "helicopter brownout" in the desert and "helicopter whiteout" in snow.
