Ultrasonic detection of icing onset and accretion thickness on aircraft

Abstract

A major environmental hazard in aviation is ice buildup on aircraft. The development of a detector for the onset of icing and for accretion thickness measurement using ultrasonic waves is described. The detection is based on reflectivity change at a metal–ice interface and based on echo-ranging techniques using pulses of longitudinal and shear waves. The detector is sensitive to the onset of icing; ice layers as thin as 0.002 in. can be detected and accurate thickness can be measured from 0.015 in. onward. By using the ratio of an interface echo and an echo from an internal reference reflector, the quantitative measurement results are immune to changes in transducer coupling conditions. Using a combination of longitudinal and shear waves, the detector can also differentiate between ice and water. Laboratory tests were made for anticipated complications, such as rough or tilted surface of ice buildup and accretion of glaze versus rime ice. [Work supported by an Army SBIR grant to J-Tec Associates, Inc.]