German Researchers Develop New Approach to Detecting Ice Accumulation in Flight

March 28, 2024

Researchers at the German Aerospace Center (DLR) have developed a new approach to detecting ice formation resulting from the accumulation of large droplets of supercooled water on an aircraft. The new sensors were developed following a European Union (EU)-wide research project involving 16 other participants addressing the challenge of detecting ice formation resulting from Supercooled Large Droplets (SLD) in positions where aircraft ice protection systems cannot reach.

The EU project, Sensors and Certifiable Hybrid Architectures for Safer Aviation in Icing Environment (SENS4ICE), featured 10 different technologies from the 16 project participants designed to directly detect ice in flight. They then successfully tested them in icing wind tunnels under both small droplet and SLD icing conditions.

One of these new technologies is the Local Ice Layer Detector (LILD), developed by the DLR Institute of Lightweight Systems, which can be integrated onto aircraft structures such as wings or tails. The LILD analyzed how ultrasonic waves are influenced by aircraft icing, that is, how they change as ice accretes on the aircraft. Other researchers developed aircraft sensor technologies based on thermal, optical and electrical principles, while some methods investigated the identification of SLD conditions using satellite data – which would also improve weather forecasts.

New Software Infers Ice from Aircraft Performance

Scientists at the DLR Institute of Flight Systems developed a new approach to determining icing conditions and the impact that they have based on the performance of the aircraft. They developed software with a monitoring algorithm that continuously analyses aircraft performance, with which they would then infer its icing condition. Ice accretion causes deviations from the normal flight state, and with this the ice could be detected indirectly.

Particularly innovative was the project's hybrid approach: by combining different detection technologies they benefitted from individual technology advantages such as precision and quick detection, but they also got more robust overall results. "Hybrid ice detection is a very promising approach for reliable and early warnings in the case of rare SLD icing conditions," concludes Carsten Schwarz, Project Coordinator for the DLR Institute of Flight Systems.

Two test campaigns were conducted in flight, specifically when flying through clouds of Supercooled Large Droplets – however, these conditions are rare and difficult to predict. The DLR Institute of Atmospheric Physics coordinated a team of meteorologists and scientists who provided essential support by forecasting the weather before the flight tests and of particular use, in real-time. For both flight campaigns, atmospheric conditions were measured with dedicated high-precision microphysics instruments. This data constitutes the reference material used to evaluate new ice detection technologies.

Flight Test Campaigns in North America and Europe

In February and March 2023, a Phenom 300 light jet, operated by Embraer, conducted 15 flights in North America, totaling 25 flight hours. In Europe, the ATR 42 environmental research aircraft from SAFIRE (the French facility for airborne research) also conducted 15 flights over about 50 flight hours in Southern France in April 2023. Combined, both campaigns flew for more than 14 hours in icing conditions and more than two and a half hours in SLD conditions – valuable time during which they were able to collect data and successfully test their technologies.

The new sensors and systems open up far-reaching potential applications - not only for the certification and safe operation of future commercial aircraft and in view of the challenges of future energy-efficient and sustainable aviation – but also for new types of aircraft, such as in the areas of unmanned or electric vertical takeoff and landing (eVTOL) aircraft.

"The best results were achieved by combining the detection of atmospheric icing conditions with the identification of actual ice accretion on the aircraft, additionally supported by monitoring the aircraft’s performance," concludes Schwarz. "The data and experience gathered made it very clear that further research into the specific SLD icing conditions is required to gain a deeper understanding. It is already clear that understanding not only the atmospheric conditions and ice build-up on the aircraft, but above all the effects on the flight characteristics are crucial for ensuring safe flight operations."

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