Rotor Control and Rotor Dynamics

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.
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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.
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Rotor test stand in the cooling chamber after a de-icing test using waste heat
The first technology investigated for alternative concepts for energy-efficient heating of the blades uses the abundant and normally unused waste heat from systems installed in the helicopter for thermal de-icing of the rotor blades. A new aspect of the investigated idea was the tapping of the gear oil as a heat source. The heating fluid heated in a closed circuit is pumped via fluid lines to the leading edge of the blade for de-icing (left rotor blade). The right-hand rotor blade is kept permanently ice-free by conventional electric heating foils to prevent sudden imbalance due to ice shedding.
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The Rotor Control and Rotor Dynamics Group of the Helicopter Department at the Institute of Flight Systems conducts research in the field of rotor dynamics of rotorcraft (helicopters & wind turbines), the integrated design and evaluation of rotorcraft configurations (including model generation), the de-icing of rotors and the intelligent control of wind turbines and wind farms.

For the simulation and evaluation of rotorcraft, the group uses its own highly modular research code MAECOsim, which can be used to aeromechanically simulate classic helicopter configurations with main and tail rotors, as well as unusual rotorcraft configurations with multiple rotors for lift and propulsion, and wind turbines. Several DLR institutes and universities are involved in the further development of the research code. There is also close co-operation with the industrial partner Airbus Helicopters Deutschland.

The design environment IRIS (Integrated Rotorcraft Initial Sizing) developed in-house is used for the integrated design and configuration evaluation. It is used to generate innovative concepts, for example a newly designed helicopter for primary air rescue, a multi-rotor configuration as an emergency ambulance and a compound helicopter for high flight speeds. The integrated capabilities of the IRIS design environment are constantly being expanded for this purpose.

One of the group's research topics is also the development of control algorithms for wind turbines and wind farms, which, for example, extract a specified power from the wind while minimizing the mechanical load on the tower, blades and actuators. Access to the turbines at the DLR Wind Energy Research Park Krummendeich means that the theoretical investigations can be supplemented by field tests.

For the development and experimental testing of energy-efficient ice protection concepts for helicopters and sensors for detecting ice build-up, a unique icing test rig for rotors was set up at DLR, on which the Rotor Control/Rotor Dynamics Group tests technologies and systems for de-icing and ice prevention on rotor blades with a radius of up to 1.9 meters.

Contact

Marc Höfinger

Head of Department
Institute of Flight Systems
Rotorcraft
Lilienthalplatz 7, D-38108 Braunschweig

Dr.-Ing. Klausdieter Pahlke

Head of Department
German Aerospace Center
Institute of Flight Systems
Rotorcraft
Lilienthalplatz 7, D-38108 Braunschweig