"David CL Francis" wrote in message
...
The extreme of this is the enclosed fan where the
enclosure markedly reduces tip losses. The fan runs nicely along like
this with a high blade area and little daylight visible through the
disc.

Whatever happened to the concept of piston engines running
a ducted fan? That aerocar thing has them, but what about
on other more normal planes?

How efficient is a ducted fan compared to a prop? I seem to
remember hearing in model aircraft settings, a prop is more
efficient.

Paul