An Analytical And Experimental Evaluation Of Airfoil Sections For Helicopter Rotor Application

The NACA 0012 airfoil section was selected for early helicopter rotor application and was used almost exclusively from 1939 . to the mid 1960's. Alternate airfoils were hardly considered during this period because aerodynamic problems were secondary to the many mechanical and structural problems related to flight controls, power systems, and structural life. In about 1965, aerodynamic considerations resulted in the use of the NACA 23012 airfoil on one operational helicopter. From about 1965 to the present, a new effort has been made to define more effective airfoil sections for helicopter rotors and to identify a systematic approach to rotor airfoil design and selection. As part of this effort, an analytical investigation was conducted to define the lift coefficient – Mach number characteristics of airfoils of potential interest for helicopter application. These characteristics were considered initially because analytical techniques could be applied. The objective of this study was to determine the relative importance of airfoil parameters such as thickness, thickness distribution, leading-edge radius, camber, and camber distribution on lift-Mach number characteristics while observing pitching-moment constraints consistent with helicopter rotor requirements. Subsequent to the analysis 7 three airfoils were evaluated experimentally. A review of the analysis and experiment is presented in this paper.