Rotor Airfoil Optimization: An Understanding of the Physical Limits

Recent airfoil design and test experience offer a new insight into the potential and limitations of helicopter rotor airfoils. The new sections have been optimized for high lift at M=0.4 and extended drag-divergence Mach number boundaries, while retaining low sectional pitching moments and acceptable profile drag. This paper reviews the key sectional characteristics of the new airfoils and it identifies areas in which improvement is still possible.