A simple method to estimate the airfoil maximum drag coefficient

A relatively simple method is presented to predict the maximum two-dimensional drag coefficient of an airfoil only using its shape. The method is based on a contribution related to the leading edge thickness in terms of the y/c coordinate at x/c=0.0125 and a contribution related to the trailing edge flow angle which appears also to be sensitive to the leading edge thickness. The relations were deduced from measurements in the Delft low-turbulence wind tunnel. The first contribution was established using 3 airfoil models with systematically varying leading edge y/c coordinates and a zero trailing edge angle. The second followed from measurements of one of these airfoils equipped with sheet metal flaps of various flap deflections. Compared to measurements found in the public domain differences are found up to ? 2.3% with an average of about-0.2%.