My Velocity SEFG airplane had a cooling problem.  The cooling air for the IO-360 engine came through two NACA style ducts in the top of the fuselage as seen in the photos. The air then  flowed down  through the cylinders and exhausted out the rear of the fuselage about 2” in front of the propeller.  I had flown the plane for about 3 years and it had always run hot.

 

I tried adding external scoops on the rear edge of the NACA ducts and that helped but looked crude and not very elegant as the NACA ducts were supposed to be a low drag, internal scoop. When I painted the airplane, after 3 years in primer (a color I called “blotch white”) I took the scoops off. The combination of no external scoops and a smooth paint surface made the NACA ducts very ineffective.

 

My engine was overheating (above 425 degF on the cylinder head temperatures (CHTs)) on climb out and cruise. This led me to a study of different methods to get more air through the engine.

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After some experimentation I developed a set of four tall vortex generators in front of the NACA scoops. They worked well. The average CHTs were lowered an average of 55 degF.

 

There are two versions of the paper that describes the vortex generators.  The first is a complete report and the second is as-printed in KitPlanes magazine.