Tony,

Here are some of old NACA references that have good info on duct and cooling system design.  You have to wade through some theory to find the gems.

- Getting rid of rumble in belly ducting.  Looks like it was NACA investigating early P-51 belly-scoop design problem.  They moved the inlet away from the belly and redesigned the shape of the duct inlet to eliminate the rumble caused by boundary layer turbulence.  Has pictures like your diagram on pages 14-17.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092694_1993092694.pdf

- Cooling Ducts - Boundary Layer Effects, NACA.  Page 16 has a good diagram.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930093223_1993093223.pdf

- Method for Design of Cooling Systems, NACA.  Page 27 has a pic showing pressure distribution across a duct like yours.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930093155_1993093155.pdf

- Basic duct theory:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930090921_1993090921.pdf

- Excellent "How-To" on designing your own NACA ducts for cooling (not exactly what you're looking for, but could be useful).  See diagrams on pages 31-35.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930093809_1993093809.pdf

- Wing-duct Cooling System.  Page 21 shows how guide vanes can be used to redirect airflow.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930081737_1993081737.pdf

Chris Sargent

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]On Behalf Of tonyslongez@cox.net
Sent: Thursday, May 03, 2007 7:35 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Cooling area drag

Ed

 How does this look? Do I have the right idea ?

the drawing is not to scale but that's the jist of it.


Tony