Airfoil performance degradation by supercooled cloud, drizzle, and rain drop icing

A wind-tunnel test was conducted to determine the performance degradation of a scaled two-dimensional NAC A 23012 airfoil (outboard wing section of the Wyoming King Air 200T) resulting from various liquid hydrometeor sizes. The hydrometeor sizes consisted of cloud, drizzle, and rain drops. The NASA Lewis Research Center's LEWICE 1.6 computer code was used to predict the ice shapes based on natural distributions obtained by the Wyoming King Air. The tests were conducted for angles of attack between —2 and +18 deg. Test results showed a moderate reduction in CLmax for the cloud, drizzle, and rain drop ice shapes; however, the rain drop (or freezing rain) ice shape delayed flow separation when compared to the cloud and drizzle shapes, resulting in a higher angle of attack at stall. Profile drag increased by 5 35% for the cloud drop ice shape, 48-56% for the drizzle ice shape, and 10-42% for the rain ice shape. After a simulated de-icing boot activation, test results showed a 50% reduction in CLmax for the residual drizzle ice shape and 34% reduction for the residual rain ice shape. Profile drag increased by up to 790% for the residual drizzle ice shape and up to 590% for the residual rain ice shape. The residual cloud ice was assumed to be cleared by the de-icing boot activation. These results do not support the current aircraft community belief that freezing rain causes the most severe icing conditions. On the contrary, aircraft encounters with supercooled drizzle, or freezing drizzle, may result in the most severe icing.