Two-dimensional airfoil performance degradation because of simulated freezing drizzle

Wind-tunnel tests were conducted to determine the performance degradation o f a scaled two-dimensional NACA 23012 airfoil (outboard wing section of the Wyoming Ring Air 200T) resulting from 1) ice because of various liquid hyd rometeor sizes, 2) simulated drizzle ice roughness, and 3) simulated drizzl e ice accretions on a model spar strap. The Wyoming King Air is equipped wi th a Saunders Fail-Safe Spar Strap that protrudes roughly 6 cm below the wi ng and extends spanwise from just outside both engine nacelles and may coll ect ice in large drop regions. The wind-tunnel evaluation facilitated quant ifying the effects on aircraft performance degradation because of the King Air spar strap. The airfoil evaluations show that the drizzle drop ice shap e and simulated drizzle ice roughness resulted in the highest performance d egradation. In general, the ice shapes and simulated freezing drizzle rough ness increased profile drag, reduced angle of attack for maximum lift coeff icient, reduced the maximum lift coefficient, altered the pitching moment, reduced lift over drag ratio, and marginally changed the lift curve slope. These evaluations also show that the most sensitive surface location on an airfoil is on the suction side between 6 and at least 11% of chord, Ice con taminations In this area are beyond the protective de-icing boots of most a ircraft and lead to severe degradations in lift and drag characteristics. T n addition, these results suggest that an ice-contaminated spar strap will increase King Air drag by approximately 12% at angles of attack consistent with cruise. Furthermore, any ice that forms on the lower surface of the wi ng, forward of the spar strap, does not significantly increase profile drag .