Modern Testing Approaches Used to Characterize Dynamic Stall Regimes on Helicopter Airfoils

Three helicopter airfoils were selected to investigate an approach to characterize dynamic stall phenomena using unsteady pressure and phase-locked flow-field measurements. The entire process was designed to ensure low cost and time efficiency in performing many measurements over many airfoils. To achieve these requirements, many sections of the blade were manufactured using rapid prototyping, and pressure measurements for all airfoils were gathered through two remotely located electronic scanning pressure modules. A modern pressure correction method estimated the time accurate surface pressures, and the total uncertainty of the pressure measurements was determined. The pressure measurements agreed well with past surface mounted pressure transducer studies that showed strong dependence on surface location and flow conditions. By combining the pressure and flow-field results, differences in stall were observed between the three airfoils, and flow features responsible for these changes were identified. The result of this work suggest that this approach offers a means of rapidly acquiring information about specific airfoils with a level of detail sufficient for understanding the complex processes experienced by these airfoils.