German scientific research centre Fraunhofer Institute is exploring several novel technologies to prevent ice build-up on wings.

The researchers are focusing particularly on anti-ice systems for composite airframe structures, where conventional installations - bleed air-heated leading edges or pulsating rubber mats which mechanically break off built-up ice - will be unsuitable.

The first development is an electrically heated leading edge, which has reached temperatures up to 120˚C (248˚F) in initial laboratory tests. What is surprising about the technology is that no metal has been used to conduct electricity and generate heat. Instead, the scientists have integrated an "electro-conductive layer of nanomaterials" into the composite plies of the leading edge.

The Fraunhofer Institute for Structural Durability and System Reliability in Darmstadt would not disclose which exact substances have been included, but Martin Lehman, the centre's deputy head, says the technology is entirely based on composites and so will not lead to fatigue issues which can arise when metals are combined with composite structures.

The wing heater has been trialled in initial windtunnel tests where water was sprayed on to the airfoil section in temperatures as low as -18˚C. The system was able to melt existing ice build-up on the wing as well as prevent formation of any new ice.

The Fraunhofer Institute for Manufacturing Technology and Advanced Materials in Bremen will soon start an EU-funded project to further develop pulsating anti-ice surfaces. Scientists want to use new materials such as shape-memory substances which change their volume when triggered by, for example, certain temperatures or electrical current. Stephan Sell, a specialist for paint, says the technology could cut energy consumption over a conventional, mechanical rubber mat by up to 80%.

The institute also wants to design an optical sensor-based ice warning system, which not only notifies flightcrew of ice accretion in real-time but also monitors the de-icing process.

Another area will be the development of water-repellent coatings to prevent run-back ice on the upper wing surface. This can happen when ice melts on heated leading edges and the water runs downstream across the cold wing skin, where no active anti-ice systems are installed.

Sell says hydrophobic coatings can be created by blending additives, such as fluorinated compounds, into the surface paint. But he adds that the challenge is to design sufficiently durable coatings, which keep their qualities over long periods in spite of environmental influences, such as erosion and UV radiation.

Fraunhofer Institute is building an ice-chamber which can simulate temperatures as low as -20˚C and wind speeds up to 70m/s (136kt).

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Source: Flight Daily News