Jim Brewer wrote:

Paul,
Thought you might be interested in the use of NACA ducts in an auto.  Check
this site:
http://www.longeze.com/Preparation/Engine/Lycoming/Cooling/cooling.html

Picture number 2.

Jim Brewer

Air cooled engines do not impede the flow of air as much as a rad so
a NACA duct works fairly well in this application.

What is dumb however is to take the air in at the bottom of most air-cooled
engine and allow it to flow first over the exhaust pipes and then
up through the cooling fins. Some air-cooled engines have the exhaust
on the top so this works fine. Most have it on the bottom however.

In theory is is better take the air in above the wing.
Unfortunately that is a low pressure area during climb so you are
in a rock and a hard spot. Best to take the air in the bottom and
somehow duct it over and down through the cylinders with the exhaust
on the bottom of the engine. 

Paul Lamar
 
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