Two-Dimensional Airfoil Performance Degradation Because of Simulated Freezing Drizzle

Abstract

Wind-tunnel tests were conducted to determine the performance degradation of a scaled two-dimensional NACA 23012 airfoil (outboard wing section of the Wyoming King Air 200T ) resulting from 1 ) ice because of various liquid hydrometeor sizes, 2 ) simulated drizzle ice roughness, and 3 ) simulated drizzle ice accretions on a model spar strap. The Wyoming King Air is equipped with a Saunders Fail-Safe Spar Strap that protrudes roughly 6 cm below the wing and extends spanwise from just outside both engine nacelles and may collect ice in large drop regions. The wind-tunnel evaluation facilitated quantifying the effects on aircraft performance degradation because of the King Air spar strap. The airfoil evaluations show that the drizzle drop ice shape and simulated drizzle ice roughness resulted in the highest performance degradation. In general, the ice shapes and simulated freezing drizzle roughness increased proe le drag, reduced angle of attack for maximum lift coefe cient, reduced the maximum lift coefe cient, 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 contaminations in this area are beyond the protective de-icing boots of most aircraft and lead to severe degradations in lift and drag characteristics. In 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 wing, forward of the spar strap, does not signie cantly increase proe le drag.