Flight testing a lamb wave based ice accretion sensor

Abstract

Although modern aircraft have ice protection systems, icing is still a concern today. The reason therefore is constituted by the fact, that ice protection systems can be overwhelmed in severe icing conditions, especially conditions with supercooled large droplets (SLD). In this case water can freeze behind the protected zone or block simpler mechanical deicing systems. For that reason, recognizing icing conditions and assessing their severity as fast as possible is a necessity. This can be achieved by ice sensors, which can help to limit the activation time of ice protection systems to the required time to save fuel or allow to escape severe conditions where the ice protection systems are approaching their limit.

Within the EU project SENS4ICE a variety of ice sensors were developed for wind tunnel and flight testing. One of these sensors is the Local Ice Layer Detector (LILD), which operated based on sending lamb wave pulses though an icing prone aircraft surface, such as a leading edge of wing or empennage. An ice accretion alters the wave transmission behavior, which can be used as a detection method. This sensor was developed and flight tested within the project.

The paper will present the basic design and measurement principle. The main focus will be on the layout and calibration of the flight test setup. The flight test sensor setup was calibrated in an icing wind tunnel to provide reference data for the flight test. Ground tests with the sensor installed on the aircraft flights in clean air without icing conditions were used to adapt the sensor software to the installation on the aircraft. Finally one test flight will be presented in the paper. It could be shown, that the LILD sensor was able to detect an ice accretion in all icing encounters within the flight test campaign.