- Formulation and application of anti-contamination coating solutions based on the selected technologies: sol gel, UV-resin, ionogel, anti-stick spray, ion implantation.
Nearly 200 different formulations or application conditions have been tested to achieve the anti-contamination objectives. The coatings were mainly applied to a stainless steel substrate in the first phase of the project. The screening was carried out on the basis of the wettability of the surface (water contact angle, slide angle) and cleanability on one hand and the basic properties such and basic properties as adherence, scratch and impact resistance, and bendability on cylindrical mandrel on the other. The coatings were also applied to micro-perforated titanium in order to verify their compatibility with this specific type of substrate without clogging the holes. Based on the results, the best or optimized solutions were submitted to laboratory and durability tests.
- Durability evaluation
In addition to the cleanability effects, the durability of the coatings is crucial in aerospace applications, especially for leading edges where the material is subject to erosion, impact, UV, etc. Several test sequences were proposed to evaluate and select the best candidate coating (including mechanical and chemical resistance and accelerated aging tests).
To evaluate the coatings' fluid susceptibility, the most representative aircraft fluids, such as water, phosphate ester hydraulic fluid (Skydrol), kerosene and de-icing fluid, were used for the test. Accelerated weather tests (a combination of UV and humidity) and thermal cycling (-40ºC to 80ºC) for 1 month were performed in a second phase. At the end of these tests, the integrity of the coating and the conservation of its functionality (anti-stick/easy-to-clean) were checked. Based on the different results obtained, 3 coatings are selected for further evaluation in simulated (wind tunnel, rain, and sand erosion) and real environmental conditions (drones).
- Development of a test stand for wind tunnel and on drones
Specific test specimens have been designed and manufactured to evaluate the selected coatings in the wind tunnel under different conditions (injection of insects, water, ice, etc.). The aim of these tests is to evaluate the performance of the coatings in terms of anti-contamination and their durability against various impacts. An insect injection system has been tested and optimized. After the first series of tests on small test coupons, the best coating out of three will be selected and used for further testing on a test specimen representative of a leading edge. The same test specimen will be used on drones to enable correlation between the different tests.
A modified design of the drone fuselage has been proposed in order to be able to carry the test samples on the nose of the aircraft. A drone instrumentation plan was developed and a flight campaign was planned in areas with a high insect concentration during the summer period.
