[kach22i]

Originally Posted by Flieger

What's the benefit of an un-ducted fan?

https://en.wikipedia.org/wiki/General_Electric_GE36

The General Electric GE36 was an experimental aircraft engine, a hybrid between a turbofan and a turboprop, known as an Unducted Fan (UDF) or propfan. The GE36 was developed by General Electric Aircraft Engines...............

The scimitar shape of the fan rotor blades enabled high flight speeds (about Mach 0.75) to be obtained.................

Although the engine demonstrated an extremely low specific fuel consumption, cabin noise levels were a problem..............

From what I recall, some wanted it for the Blended Wing Body designs, but those concepts were switched to ducted fans and turbofans once the noise issue of the GE36 became known.

Blended Wing Concept



EDIT: found more...........

http://www.hfcletter.com/Content/BlendedWing.aspx

A NASA rendering of two blended wing-body planes: one a jet and the other propeller-driven. Boeing is apparently also studying hybrid electric gas turbine propulsion.