Naca scoop evaluation: expert opinions desired!

[Tom Martin]

Damon
I believe that you are on the right track. Ideally the oil cooling system would be totally independent of the cylinder cooling system. I agree with previous posters that the NACA duct may not be the ideal choice. Perhaps your friend got it in the exact right spot on his RV8. Also I note that you do not have your gear farings on at this time. The added 10 to 15 knots of airspeed could make quite a difference to your engine/oil cooling.
I would suggest that you try a straight in ram duct somewhere in the area below the #2 cylinder. This is a high pressure area and will mean that a smaller hole size will be required. I would start with a 3" round hole, that is flush to the cowling. As the area is curved the actual hole might end up being oblong in shape. From that hole, on the inside of the cowling create a gradual smooth expanding shape to the face of the oil cooler. If the cooling is adequate then the hole size/shape could be reduced to get the best average oil temperatures.
At this point it sounds like the cooler is just dumping into the cowling. Knowing the inlet and outlet pressures of your cooler will let you know if you have to have a different outlet duct on the cooler itself. This outlet duct could be to the exit area of the cowling or like I did on my rocket to the low pressure area on the side of the cowling. I used a "bluff body" ahead of the outlet and played with the shape until the cooler worked well. I believe the CAFE group did some work on bluff body extractors. If not them, then the WWII NACA studies out of Mississippi. My system does not have a separate inlet for the cooler but I would really like to add one and I am pleased to see you working in this direction. Congratulations for trying something different, it is supposed to be educational! By keeping the two cooling needs separate the ultimate goal is to reduce the total cooling flow through the engine. If you can do that, AND, have keep the exhaust air from both systems going straight aft in line with the free stream air, you should not only keep your engine cool but increase speed. Keep us posted on your efforts.