DESIGN AND EVALUATION OF MULTI-ELEMENT AIRFOILS FOR ROTORCRAFT

Helicopter airfoils with leading-edge slots have been shown to increase maximum lift coefficient significantly, but at the price of a severe drag penalty at low values of lift coefficient. A study has been conducted with the primary goal of improving the low-lift drag characteristics of a slotted airfoil while maintaining maximum lift characteristics. New high-lift airfoil technology was used, including automated grid generation methods for Navier-Stokes analysis and inverse design techniques to produce improved designs. The new slotted designs provided significant computed reductions in drag at low lift coefficients. Rotor performance evaluations using the slotted sections compared to a base-line non-slotted rotor indicated that rotor performance gains could be achieved.