SmarT Eco-friendLy anticontamination technologies for LAminar wings- STELLAR project in test at Florennes AFB

The STELLAR project aims to produce sustainable solutions to reduce drag on aircraft, allow laminar flow over time with a direct impact on fuel consumption and thus contribute to the reduction of the ecological footprint of aviation, aiming at a 50% reduction in wing friction and up to 5% less CO2 emissions.

This programme is being developed by a consortium of various players. The players are: Airbus, MATERIA NOVA, SONACA, SONACA Aircraft, Cidetec, La Mesure sur Mesure (LMSM), Von Karman Institute, UMons, SOPURA, and ESPCI Paris.

STELLAR was selected from among various development projects. These projects were funded by the European Horizon 2020 research programme for research and innovation. STELLAR was launched in October 2019 under the coordination of MATERIA NOVA with Airbus as lead manager. Materia Nova ensures technology transfer between the worlds of research and industry.

The theory: The deposition of insects is the main cause of pollution on the leading edge surface. It significantly alters the airflow distribution over the nose and continues along the entire wing surface.

In the words of Mireille Poelman of MATERIA NOVA: “This project is part of the aeronautical industry’s programme to considerably reduce its environmental impact. This translates into various strategies such as lightening structures, reducing fuel consumption, but also working on aerodynamics. By working on the profiles, we can imagine between 5 and even 10% reduction in consumption.

Research over many years has shown that profiles can be greatly improved if their surfaces are perfectly clean. The slightest residue of dust or, above all, insects will disturb this profile. This is where our project comes in. We are developing strategies to reduce this insect contamination or to facilitate its removal.

The COVID crisis has seriously disrupted the project schedule. The period chosen for these trials cannot be done all year round, but in a specific period when the quantity of insects is high. This is a two million euros project. The approach to this project is multidisciplinary. First of all, we had to understand how this contamination was created, understand the chemical aspect of the coagulation of the liquid left by the insects and then how to combat these phenomena. One of the project’s axes was to see how flight parameters, such as high speed, pressure variations and low temperatures, could influence coagulation. All this with a very large number of proteins that are found in this liquid deposited by the insects. This is where UMons and the Von Karman Institute came in.

The goal was to develop anti-contamination coatings based on an in-depth understanding of the biochemical modifications of insect hemolymph during impact and the associated physico-chemical properties. These coatings with sliding effect or self-healing properties should be applicable on aluminium, titanium or composite materials.

Carl Mengdehl of SONACA Aircraft tells us about the flight tests: “We decided to select three promising coatings and install them on three leading edges of one of our test aircraft. We also installed sensors. Then we had to find a place where we could collect as many insects as possible. This is where our collaboration with the Florennes AFB comes in. We had to be able to fly at a very low altitude (less than 10 m above the ground) above a field. Here, we had a large green area available for us, ideal for having lots of insects, but also a reasonable environment in terms of safety with a large runway available in case of problems. We did five days of testing in very good conditions during which we made between 40 and 50 passes to collect a maximum number of insects. This also served to bring back as much video and data as possible.

For data acquisition, we used a small external sensor, developed in France, which had already been mounted on Alpha Jets among others. This type of sensor does not require drilling into the surface.

The passes were made along the southern runway at a speed of 115 knots at an altitude of less than 10 metres above the grassy area.

At the end of these tests, the best of the three coatings will be applied to the leading edge of a Brussels Airlines Airbus A320 for evaluation over a six-month period on a standard airliner. SONACA will be in charge of this part of the work on the slats of the Airbus A320. The idea is to see if there is a noticeable difference over the long term. These tests will be carried out during the course of next year, depending on the most favourable period for the insects.

After a long period of testing, we could see this coating applied to the slats of future Airbus aircraft within five years.