Correlation of icing relationships with airfoil and rotorcraft icingdata

Abstract

A high-speed icing wind tunnel test program was conducted to measure the ice growth and performance degradation on 10 rotorcraft airfoil models for ranges of liquid-water content, temperature, and Mach number at several steady and unsteady angles of attack. Prior to these tests, airfoil icing data had been acquired only in low-speed tunnels or during flight testing, but high-speed data are necessary for the prediction of icing on rotors. The test explored the boundaries for the onset of icing and between glaze and rime ice. Ice shapes were documented and lift, drag, and pitching moment were measured. Airfoil lift was reduced slightly at low angles of attack and about 20% at high angles. Drag increased in moderate icing at low angles of attack by a factor of three to four, increasing for higher liquid-water contents and angles above 6 deg. The effect of Mach number varied. Airfoil oscillation did not change the lift loss, but did reduce the drag penalty. Two-dimensional airfoil icing relationships for ice thickness and for changes in lift, drag, and pitching moment coefficients were formulated, with improved accuracy over prior relationships. These relationships have been used to predict aircraft power changes during icing.