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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - PHOBIC2ICE (Super-IcePhobic Surfaces to Prevent Ice Formation on Aircraft)

Teaser

Summary

The accretion of ice represents a severe problem for aircraft, as the presence of even a scarcely visible layer can severely limit the function of wings, propellers, windshields, antennas, vents, intakes and cowlings. The PHOBIC2ICE Project aimed at developing technologies and predictive simulation tools for avoiding or mitigating this phenomenon.

The PHOBIC2ICE project, by applying an innovative approach to simulation and modelling enabled the design and fabrication of icephobic surfaces with improved functionalities. Several types of polymeric, metallic and hybrid coatings using different deposition methods were developed. Laser treated and anodised surfaces were prepared. Consequently, the Project focused on collecting fundamental knowledge of phenomena associated with icephobicity issues. This knowledge will give a better understanding of the ice accretion process on different coatings and modified surfaces. Large-scale icing wind tunnel in Canada and flight tests performed in Spain helped in developing comprehensive solutions to address ice formation issues and raised the Projectâ€™s innovation level.

The proposed solutions are environmentally friendly, they aim towards reduction of energy consumption, and contribute to the elimination of need for frequent on-ground de-icing procedures. This in turn should reduce pollution, cost, and flight delays.

The intercontinental research consortium consisted of 5 Canadian and 4 European partners from Germany, Poland and Spain.

Work performed

The objective of the first task was the specification by the industrial Partners of the list of elements to undergo coating or surface modification. The list drawn up initially consisted of 30+ proposed elements. Confronting these elements with the specific characteristics of the surface treatments and deposition techniques available within the consortium, as well as with the materials from which the components are made, the list was narrowed down to seven elements. In order to limit project costs, most work is conducted on small samples made of materials corresponding to those used in the full-scale elements. The work focuses on five materials, i.e. aviation aluminium and titanium alloys, stainless steel, carbon-epoxy composite and polyamide.

The overall research was divided into three categories, i.e. basic research which include common tests like surface topography, adhesion tests, wettability tests etc, more advanced tests including tests in icing conditions (mainly ice adhesion and accretion tests) and finally, coating durability tests e.g. corrosion resistance, degradation and UV resistance etc, performed only on those coatings that qualified in the previous two testing stages. This methodology is more efficient since it will not be necessary to test all the coatings but only those with the best performers. The most promising will be tested in two sessions by means of ice wind tunnel and during flight tests.

The research was focused on the work foreseen for the first stage, i.e. basic research. In parallel with the work within WP3 and WP4 tasks, computer simulations were conducted within the WP2 task. This work supported the practical tests aimed at developing appropriate surfaces. It also helped to better understand contact phenomena in micro and nano scale between droplet and surface.

The simulations were performed at three scales â€“ nano, micro scale and macro. In order to confirm the hypotheses, the tests conducted in 2016 consisted of simulation of droplet behaviour on initial surfaces, i.e. on materials currently used to manufacture surfaces with particular risk of icing. The behaviour of droplets on aluminium oxide (Al2O3) and titanium oxide (TiO2) were modelled.

The partners performed sequence 1 tests (basic tests) to assess the fabricated coatings and/or surface modifications. More than 700 coatings/samples were prepared and reported to AGI in order to down-select the promising coatings for sequence 2 tests including ice accretion, ice adhesion, rain and sand erosions according the guidelines specified in testing matrix (D4.3). After performing sequence 2 assessment tests and the recommendation of the coating developers, a final selection of 14 coatings were tested in sequence 3 i.e. the large-scale icing wind tunnel at NRC (Ottawa) and the flight tests at INTA (Madrid).

Final results

Overall, the consortium partners went beyond the state of the art in understanding phenomena behind icephobicity on aircraft surfaces. In addition, they were able to develop and modify coatings, several including laser surface treated ones. These yielded very attractive results on large ice wind tunnel tests and are presently waiting for real flight tests on experimental aircraft. Also, the consortium partners developed a robust multiorganization collaboration scheme to perform activities to observe, analyse and measure superhydrophobic capabilities, ice formation and accretion, ice adhesion, surface erosion in the lab environment and finally applying IWT and flight test procedures.

Based on the results achieved by project teams it was found that superhydrophobicity does not guaranty icephobic behaviour of modified surface/coatings as claim many authors in the literature. During the ice adhesion strength tests it was concluded that with increased roughness usually leading also to increased ice adhesion to the surface what is not desired effect. In some cases those conclusions led to change methodology for coatings development.

From the societal point of view the proposed solution are environmentally friendly. Mitigation or prevention of ice formation will reduce energy consumption, and will eliminate the need for frequent on-ground de-icing procedures of airplanes. This in turn will reduce pollution, cost, and flight delays. Development of passive approaches like coatings or treated components surface will increase safety, reduce the issues related to active de-icing and anti-icing technologies. It will allow to decrease or possibly eliminate the need to use de-icing fluids on ground operations which have negative environmental impact and cause flight delays. Reduce or elimination of ice accretion also in turn will result in fuel consumption reduction which is burned for heating and activation of anti-ice accretion systems.

One of the main outcomes of the Phobic2Ice project was the understanding that for speeding up the development of such a technology like functional coatings for aerospace (icephobic, but also anti-contamination, erosion resilient, drag reducing, etc.) needs the parallel development of standardized testing process for assessing the maturity and preparing the certification of such technologies. This was realized by all project partners, but also confirmed by the certification authorities like EASA or TC.

The recommendation thus derives from this understanding: we need to invest more resources in developing the appropriate testing routines to a level where we can standardize them and use them also for qualification and certification purposes. This is best done in collaboration with the certification authorities (EASA, FAA, TC, etc.).