Wind tunnel and flight testing of a lamb wave-based ice accretion sensor

Abstract Severe icing conditions are still a risk in aviation. Heavy ice accretion on aircraft can affect mass and aerodynamic performance in a way, that a catastrophic loss of control may occur. Detecting icing conditions and the extent of ice accretion is therefore essential to react instantly and to assess the severity. This eases the decision to either activate ice protection systems and continue the flight or to leave the icing conditions immediately. These functions can be provided by an icing sensor. Within the EU funded SENS4ICE project, several ice sensors have been developed. One of them is the so-called local ice layer detector (LILD). It uses lamb waves which are guided by the aircraft structure. If an ice accretion happens, the wave guide behavior is affected changing amplitude and lag time of the lamb wave pulses. This can be measured. If the sensor is mounted to a surface on the aircraft which is prone to icing, e.g. the leading edge of the wing, ice can be detected where it is relevant for the aerodynamic performance. Within the project, the sensor hard- and software have been developed to create and measure lamb wave pulses in a wide frequency range. To investigate the influence of ice accretion on the lamb waves, wind tunnel tests were undertaken. Finally, the sensor was investigated in a flight test. In this paper, an overview about the function of the sensor as well as the general signal behavior are given. The results of the wind tunnel test and some preliminary results from the flight tests will be shown. In both tests, the sensor was able to detect even very thin ice layers with minimum delay from the beginning of the ice accretion.