BIG SNIP

Another reason  NACA ducts work on canard pushers, besides the prop
sucking the air in, is the air resistance of the fins on an air

cooled

aircraft engine is probably less than the air resistance of a

radiator

with equivalent cooling capacity.

Paul Lamar

   Aircooled submarine.  ;-)

Bill Freeman

Perry Mick wrote:

The NACA has always worked great for me and my small radiator
under the engine, with ducted-fan assisted airflow.

But the NACA does not always work well for the air-cooled boys.
A lot of them are converting to armpit scoops and scoops on top
of the cowl (downdraft cooling they call it) which I guess works well,
probably only because the cylinder heads are above the top of the
strake anyway (those huge cowl bumps), so these ducts direct air
right at the cylinders.

The NACA on the belly of the Long-EZ I think was not a Rutan
original but came from someone else and was very widely copied.

--
Perry J. Mick
Duckt N7XR
http://www.ductedfan.com

That's interesting Perry. Most air cooled air craft engines are designed
for down draft cooling as the exhaust is on the bottom of the engine.
It is better if the air comes in the cool side of the engine
and exits the hot side. It works similar to a cross counter flow
radiator. The average temp difference between the hot fins and the cool 
air is higher doing it that way. I think it was Franklin that discovered 
this back in the early 30's. Lycoming built some engines with the exhaust
on the top of the engine. These were used on some twins and on the
Piper Lance I think. They are also used on some SeaWinds.
In this case they are optimized for updraft cooling.

Paul Lamar
 
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