Bill Freeman wrote:

Paul,

Just another plug for the benefit of the new folks out there for what
I think is an under appreciated inlet type - the external diffuser.
This is what the cowl on a radil engined WWII US fighter used,
and it is much better than most would think just by looking at it.

Check out the streamlines in the attached cross section view.
This can be built as a body of revolution or as extruded into
a rectangular inlet.

Bill Freeman

This is a refinement  on the gif that Bill sent and is more applicable
to a radiator. Later radial engine installations after WW II like the 
Lockheed P2V used a extended crankcase and crankshaft shaft and used 
an internal shape for the cowl more like this to effectively lower 
the drag of radial piston engine installations over the pure external
diffusion inlet described by Bill.

Paul Lamar
 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.
ACRE NL web site.
http://home.earthlink.net/~rotaryeng/            http://www.linux.org