Me: "This brings back memories of me a few years ago trying to pin down exactly what defines a propfan, and then just giving up. .... Perhaps one definite statement one can make about the distinction between turboprops and propfans is this: So far, for all engines called 'turboprops,' the axis of rotation of the propeller is offset from the axis of rotation of the compressors/turbines of the gas generator, while for all engines called 'propfans,' the axis of rotation of the propeller/fan is the same as the axis of rotation of the compressors/turbines."
Tomboy: "Not really true as from the top of my head, NK-12 and AI-20/WJ-6 has a coaxial propeller"
Now you can see why I previously gave up!
