Researchers at the Department of Automotive and Aeronautical Engineering investigate a new material of which future wing leading edges could be made, since it can provide a De-Icing function.

Application: De-Icing of aircraft wing leading edges

The aerodynamic stream bears supercooled water which hits the leading-edge surface of an aircraft wing during climb or descent through wet air conditions at low temperatures. Especially the leading edge accumulates ice in this flight phase. Excessive ice layers reduce the aerodynamic performance of the wing which could lead to hazardous failure. Accordingly, De-Icing systems are a standard part of the wing leading edge structure that are operated during the critical flight phases.

Classical De-Icing systems like the Bleed-Air system that operates with hot air taken from the engine or electrical heater mats are standard industry solutions for today’s commercial aircraft. These classical systems and new concepts in research and development usually provide a drawback: The systems are installed on top of the load bearing primary structure of the aircraft. This adds additional weight to the structure which needs to be carried during the complete flight time. Contradictory, the system is only operated during the small periods of climb and descent.

Therefore, researchers are investigating new approaches for De-Icing which are more lightweight and energy efficient. Maximilian Schutzeichel, doctoral student at the Department of Automotive and Aeronautical Engineering at HAW Hamburg, investigates a new multifunctional material within his cooperative doctoral project under supervision of Prof. Dr.-Ing. habil. Thomas Kletschkowski (HAW Hamburg) and Prof. Dr.-Ing. Hans Peter Monner (Otto von Guericke University Magdeburg).

Hidden potential in classical composite materials

Within the doctoral project, the characteristics of multifunctional carbon fibre reinforced plastics (CFRP) are examined. The physical properties that enable the use of the material for more than structural integrity are of special interest. It is well known that CFRPs offer very good mechanical performance whilst being lightweight which is also the reason for their broad application in aircraft structures over the last decades. However, besides the mechanical stiffness and strength, carbon fibres also provide electrical conductivity. Once electrical energy is transferred, the material’s temperature rises due to the Joule effect. Consequently, the use of electrical energy for heating is another function that is not applied in actual aircraft structures yet. The multifunctional application of CFRPs was already covered by an industry patent from Airbus Operations GmbH in 2019 [1].

In classical CFRPs the carbon fibres are randomly connected to each other which results in an arbitrary network of short circuits within the composite material. This prevents an efficient and directed current conduction. Researchers within electro chemistry at the Royal Institute of Technology in Stockholm developed an electrical insulation in form of a polymer coating of the carbon fibres. The coated carbon fibres function like a cable of which the conducting core is insulated from the environment. The additional coating material phase influences with its thermo-mechanical properties the effective material behaviour of the composite [2]. However, the directed current conduction enables a precise heating of the CFRP at the desired positions, which could be used as a De-Icing system for aircraft wing leading edges. To predict the physically coupled material behaviour, a physically coupled multi scale model is developed which provides insights in the characteristics of a multifunctional structure made from this material.

Prediction of the material behaviour

In order to describe the material properties with respect to the operating temperature, processes are described on the micro scale. Therefore, a representative volume element with a random distribution of coated carbon fibres is chosen (see figure 1). With this cubic representation of the material, the calculations towards effective heat transfer and mechanical properties are conducted. The effective properties are then transferred to the meso scale representation of the problem (e.g. a flat plate) to investigate the behaviour of a structure made from this material.

By the help of a flat plate specimen (see figure 2) in which carbon fibre rovings for current conduction are embedded, the multi scale model is verified with respect to aircraft icing conditions. This is enabled by an additional, cooperative investigation within the De-Icing test bed at the Technical University of Braunschweig, at the Institute of Mechanics and Adaptronics. By the help of an experimental setup, the thermal behaviour of the specimen was measured under operational conditions like air speeds of up to 35 m/s and environmental temperatures of down to -20 °C. The results of thermal measurements are compared with the predicted behaviour from the model and are found in very good agreement. The quality of this work was honoured by selecting both articles for title cover stories of the Journal of Applied Mechnics from MDPI in which the results were published [3+4].

Besides the scientific motivation of these investigations, the capability to De-Ice the surface of the specimen was demonstrated successfully. With these results as a fundament, the interaction of electrical, thermal, and mechanical effects can be analysed by the help of the multiphysical multi scale model. Besides the objective of an energy efficiency increase, the revelation of critical material behaviour under multiphysical load conditions is of special interest. Only by a proof of strength and durability, the material could be applied in future aircraft wing structures.

What’s next?

The driver of further investigations is the analysis of a potential mass reduction and an energy efficiency increase by the application of the multifunctional composite material e.g. for De-Icing. Latest investigations support the assumption that up to 50 % of energy consumption and up to 80 % of weight of the De-Icing system could be reduced by this technology. This potential is motivated by the fact that no additional mass needs to be installed on the load bearing structure to enable the De-Icing function, since it is enabled by the load bearing material itself. In addition, it is expected that the internal architecture of the material can be optimised such that a most efficient use of the heating energy is possible. These objectives are part of the ongoing research work in order to reveal the quantitative benefits of the multifunctional composite.

via: HAW Hamburg

 

 

 

[1] Schutzeichel, M.O.H.; Linde, P.: Heatable Leading-Edge Apparatus, Leading-Edge Heating System and Aircraft Comprising Them, Applicant: Airbus Operations GmbH, Application Nr.: CN201910526359 20190618

[2] Schutzeichel, Maximilian Otto Heinrich; Kletschkowski, Thomas; Linde, Peter; Asp, Leif E.: Experimental Characterization of Multifunctional Polymer Electrolyte Coated Carbon Fibres. In: Functional Composites and Structures 1 (2019), Nr. 2, 025001

[3] Schutzeichel, Maximilian Otto Heinrich; Kletschkowski, Thomas; Monner, Hans Peter: Microscale Thermal Modelling of Multifunctional Composite Materials Made from Polymer Electrolyte Coated Carbon Fibres Including Homogenization and Model Reduction Strategies. In: Applied Mechanics 2 (2021), Nr. 4, S. 739–765

[4] Schutzeichel, Maximilian Otto Heinrich; Strübing, Thorben; Tamer, Ozan; Kletschkowski, Thomas; Monner, Hans Peter; Sinapius, Michael: Experimental and Numerical Investigation of a Multifunctional CFRP towards Heat Convection Under Aircraft Icing Conditions. In: Applied Mechanics 3 (2022), Nr. 3, S. 995–1018