Clark-Y Airfoil Characteristics

These data were taken at four differnet values of the Reynolds number (Re). The values span the range that most control line propellers will experience. The prominent feature is the large increase in airfoil performance with increases in Re. No choice of airfoil shape can possibly add this kind of benefit. The message is clear. In the portions of the propeller just inboard of the tip the best performance is associated with large chord.

Note that operation at the best lift/drag ratio would mean operation on the virge of a stall. This is common - almost universal - at low Re. Because of this the operating angle of attack must be lower to provide some margin aginst stall in operation