Charlie,

If you have a turbine type cowl then moving the inlets to the belly duct should not increase the flat plate area.  At least that’s my theory.

Bobby Hughes

N416AS RV10 223 hrs

Mind you, my rotary is not flying yet and I have a Canard design but I often wonder why the RV guys don’t relocate the radiator and use a P-51 style scoop?

I’ve seen many that have the radiator almost perpendicular to the direction of the inflow.

I would think that a radiator mounted just behind the seats would give you the distance to properly expand the air and recover the pressure more efficiently.

 

Just thinking out loud ......

 

T Mann

I agree, a perfect P-51 style setup would be better, but....

Ross Farnham in Canada has done it (sort of).
http://www.sdsefi.com/air9.html
http://www.sdsefi.com/rv17.htm
http://www.youtube.com/watch?v=QT8njoirTkU
http://www.youtube.com/watch?v=gPpWHvr1kJw
He won't publish hard numbers, but has vaguely hinted at a 6-8 knot speed gain over his old cooling system, which was pretty convoluted (multiple air inlets/outlets in random places for multiple random heat exchangers), so it was probably a net 0 gain over a well done under-cowl setup.

It's pretty complicated to run the plumbing, and since a complete rotary installation that's built with careful attention to weight can come in lighter than a Lyc (I put my entire FWF on a scale: 310 lbs, dry), moving the heat exchangers aft is likely to adversely affect the CG. Ross got away with it because he's running a turbo Subaru, which is pretty heavy.  The P-51 rad is partially submerged in the fuselage. Submerging the rad in the aft fuselage sounds great, but even if you can deal with the CG issues, with a metal fuselage you have to be very careful what & where you cut to get the air in & out. And the scoop itself is extra weight (the cowl is already there for the outside of the 'scoop').

Water cooled engines beg for an airframe designed around them, just as air cooled engines have planes designed around them.

Charlie