Ice formation on aircraft poses a significant safety risk – for both helicopters and fixed-wing aircraft. It can severely affect aerodynamics, controllability, and system functionality. To address these challenges, the DLR Institute of Flight Systems develops and tests innovative icing and de-icing technologies. In this field, the Institute is conducting research into practical solutions for the detection, analysis, and removal of ice.
Monitoring Aircraft Icing During Flight
Icing of fixed-wing aircraft – especially caused by supercooled large droplets (SLD) – can pose a significant safety risk in flight. For years, the Institute of Flight Systems has been involved in international research on this topic and has explored various approaches for simulating and analysing flight dynamics under icing conditions affecting different aircraft surfaces.
Most recently, the institute coordinated the EU project SENS4ICE (SENSors and certifiable hybrid architectures for safer aviation in ICing Environment), in which novel technologies for the detection of SLD were investigated in collaboration with 16 other project partners. As part of this effort, the institute developed an innovative aircraft-based approach for ice detection: a performance-monitoring software capable of reliably identifying icing on the aircraft in an indirect manner. This approach was successfully demonstrated in flight tests and is considered a promising technology by both industry and certification authorities.
De-icing of Rotor Blades
De-icing systems for rotor blades must meet stringent requirements in terms of weight, size, and power consumption, especially for small and medium-sized helicopters. The rotor tower at the DLR Institute of Flight Systems houses a test rig that allows the testing of rotors with a diameter of up to 4.2 metres. This facility has been expanded into a test stand specifically for the icing and de-icing of rotor blades.
To this end, a deep-freeze chamber was installed in the tower, enabling experimental investigation of de-icing technologies for rotor blades under realistic atmospheric icing conditions at temperatures as low as -25°C. A spray system mounted below the ceiling can disperse a water-air mixture, which leads to controlled icing conditions.
This test stand – unique in Europe – marks a departure from the conventional method of testing de-icing systems on non-rotating profiles in wind tunnels. It introduces centrifugal loads into the process, allowing the influence of centrifugal force on the energy requirements for de-icing to be taken into account. This enables the development of more efficient and energy-saving systems.
Ice formation on the leading edge of the tailplane of the Safire ATR 42 in flight
Icing during flight can lead to impairment of flight performance and flight characteristics.
Rotor test rig and spraying system in the cooling chamber inside the rotor tower
The rotor test stand within the cooling chamber enables the testing of technologies for de-icing/anti-icing under the influence of centrifugal acceleration as well as sensors for ice detection. The spraying system under the cooling chamber ceiling, equipped with 15 heatable nozzles on a circular structure, enables the simulation of realistic atmospheric icing conditions through the controlled injection of air-water mixtures. The temperature in the cooling chamber can be lowered to as low as -25°C for this purpose.
Iced rotor blade in the DLR rotor icing test facility
When supercooled water droplets hit the rotating rotor blades, they freeze abruptly. Depending on the temperature, the liquid water content (LWC) in the air and the median volume diameter (MVD)in the spray, a steadily growing layer of ice forms relatively quickly, primarily on the leading edge of the blade. Depending on the temperature inside the cooling chamber, clear or rough ice or a mixture of the two is formed. Although this form of blade icing is beautiful to look at, it poses a danger to the aircraft if it is not recognized in time and appropriate countermeasures are not taken quickly.
