AIRFOIL PERFORMANCE DEGRADATION BY SUPERCOOLED CLOUD, DRIZZLE, AND RAIN DROP ICING

A wind-tunnel test was conducted to determine the performance degradat ion of a scaled two-dimensional NACA 23012 airfoil (outboard wing sect ion of the Wyoming King Air 200T) resulting from various Liquid hydrom eteor sizes. The hydrometeor sizes consisted of cloud, drizzle, and ra in drops. The NASA Lewis Research Center's LEWICE 1.6 computer code wa s used to predict the ice shapes based on natural distributions obtain ed by the Wyoming King Air, The tests were conducted for angles of att ack between -2 and +18 deg. Test results showed a moderate reduction i n C-Lmax for the cloud, drizzle, and rain drop ice shapes; however, th e rain drop (or Freezing rain) ice shape delayed now separation when c ompared to the cloud and drizzle shapes, resulting in a higher angle o f 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 min ic e shape. After a simulated de-icing boot activation, test results show ed a 50% reduction in C-Lmax 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 he clea red by the de-icing boot activation. These results do not support the current aircraft community belief that freezing rain causes the most s evere icing conditions. On the contrary, aircraft encounters with supe rcooled drizzle, or freezing drizzle, may result in the most severe ic ing.