Dec. 15, 2003
Used oil was brushed on areas of the belly of the plane ahead of the regions where air flow was to be monitored. The plane was then flown normally for about 30 minutes. After landing, the oil flow patterns were photographed. Tests were performed with and without an air baffle installed. The air baffle used in the test was temporary. It was constructed of a piece of cardboard and attached with duct tape.
A significant feature is noted in the area where the width of the NACA scoop becomes nearly constant. Without the installation of the corner baffle, the oil is blown away from the edge of the NACA scoop, indicating that the air in the scoop is spilling out and interfering with laminar flow along the belly. More significantly, without the baffle, the air is not flowing into the cowl and cooling effectiveness is being lost. In addition, drag is increased by the resulting turbulent air.
Placement of a simple, triangular baffle prevents the air from spilling out of the NACA scoop. An added and important benefit is that cylinder head temperatures are lowered by about 30 degrees for each cylinder.
The tests are preliminary, and the optimum size and shape of the baffle has not been determined. Any suggestions as to size, shape and placement would be appreciated. The cardboard/duct tape inserts were replaced with permanent fiberglassed foam inserts 3/4" thick. These were later reduced in thickness to about 1/8" at the leading edge and tapered from the leading edge back to the thickness of the inlet lip. Oil flow tests are shown for both configurations.
Note: After completion of the tests, I learned that Klaus Savier had already recognized this NACA loss as a problem and had made similar modifications.
Without Corner Baffles.
Showing the Effect on the flow
With the addition of Vortex Dams
Click on each photo for an enlarged view
