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

Kurzfassung

Ice accretion happens, when atmospheric water freezes on structures. If the ice accretion is too heavy, it can lead to a functional degradation or even a catastrophic failure of the structure. This is especially the case in aviation, where airplanes regularly encounter freezing temperatures in the air as well as atmospheric water in the form of precipitation, snow or condensation. It is easy to understand, that ice accretion on an aircraft in flight has to be prevented by any means, since the ice heavily degrades the aerodynamic performance by reducing lift and increasing drag, but also adds to the aircraft weight. Therefore, aircraft have de-icing and anti-icing systems to either remove ice or prevent the accretion. For both means detecting an ice accretion in time by specialized ice sensors is crucial. Furthermore ice sensors could help to limit the operation of power intensive ice protection systems to the required time allowing to save energy and fuel. Within the EU project SENS4ICE, different icing sensors are developed and tested, of which one will be presented in detail in this paper. It is based on sending ultrasonic lamb waves through a structure, which is prone to ice accretion. This so-called Local Ice Layer Detector (LILD) was then developed from a basic laboratory setup to wind tunnel and flight tests. To achieve this, a dedicated sensor hardware had to be designed and built which allows a standalone operation. This is needed as a sensor. Additionally the electronics unit was required to be compatible with flight testing. With this electronic unit, icing wind tunnel tests were performed to investigate the behaviour of the lamb waves in different temperatures and icing conditions. Based on the wind tunnel tests, the detection algorithm for ice was designed. In the wind tunnel tests, the LILD sensor was able to detect the presence of ice in all measured cases. The required ice thicknesses for a reliable ice detection were found to be well below 1 mm. After the wind tunnel tests, a final iteration on the sensor hardware was done before it was fitted to the flight test. The flight tests were performed using an ATR42 aircraft from Toulouse Francazal airport in April 2023. Hereby the sensor electronics were situated within the cabin of the aircraft for protection and checks by the operators. As the test surface, the leading edge of an underwing pylon was used where the lamb wave transducers were mounted to from the inside. In this flight test campaign, 50 hours of actual flight time could be completed with a variety of different icing conditions. Based on a first evaluation of the flight test data, the LILD sensor was reliably able to detect ice accretion and the presence of ice in line with the reference probes and the other ice sensors mounted on the aircraft. The paper will present the basic design of the sensor and provide an insight about the aforementioned experimental results in the wind tunnel and flight test campaign.