Shark meets crane
Highly automated application process for innovative painting system
Continuous improvement of the drag factor of aircraft has been ongoing for many years, with various measures being adopted, so that aviation is becoming more and more fuel-efficient and environmentally friendly. With the EU‘s "Clean Sky" project, Lufthansa Technik focused its efforts on investigating new aircraft surface coatings in the "Multifunctional Coating" research project, succeeding in 2011 with the drag-reducing "riblet" structure, better known as the sharkskin structure. The findings from the "Multifunctional Coating" project demonstrated both the stability of the material and the "riblet" structure and their sustainable economic viability.
In the "Multifunctional Coating" research project, Lufthansa Technik used 10cm x 10cm patches on the fuselage and wings to conduct its tests. Now, larger-scale applications are being prepared. For this purpose, Lufthansa Technik has joined forces with Bremer Werk für Montagesysteme GmbH (bwm) and Airbus Operations GmbH to establish the successor project, "FAMOS" (guidance system for the automated application of multifunctional surface structures). The goal of "FAMOS" is to develop a comprehensive, highly automated system for cleaning, stripping, painting, and applying low-drag aircraft surfaces. Furthermore, the new system is to facilitate the direct printing of photo-realistic images on the aircraft outer skin.
For the new surface coating, Airbus has cooperated with Fraunhofer IFAM to develop a special painting system which is hardened by UV light, does not contain any liquid solvents, and fulfils the intense demands imposed by aviation. A new process has been developed for the application of the micro-structured paint layer on the surface. This process, the "Simultaneous Stamp Hardening Method", transfers the microstructure to the lack precisely. The paint is applied with a stencil die bearing a negative of the riblet structure and then hardened with UV light before the stencil die is removed. The process is currently being carried out manually, which means that it can only be used on small surfaces. In the future, a robotic guide arm will be used to automate the entire process with all its steps. This is the only cost-efficient way to achieve larger scale coating with the required quality.
The "FAMOS" research project, funded by the Federal Ministry of Economic Affairs and Energy (BMWi), is being conducted within the first call of the fifth German Federal Aeronautical Research Programme (LuFo V) from January 2014 to March 2017. In the first project phase, the constraints for all work are being documented and the research goal defined in detail, based on a requirements analysis and the technology currently available. Finally, the possibilities for a future industrial implementation of the project are to be tested and precisely assessed in a real-life setting using a demonstrator with limited functionality.
The new surface coating of aircraft with low-drag microstructures can lead to fuel savings of around one percent. This means that the deployment of this technology for Lufthansa Passage alone, where more than six million tons of kerosene are consumed each year, can result in an annual saving of 55 million euros in fuel costs. Furthermore, this financial benefit is accompanied by a reduction in CO2 emissions of some 200,000 tonnes. If "FAMOS" can be successfully completed and the paint-based surface coating can be developed into an industrially viable product, Lufthansa Technik and Airbus will be the first to deliver the "riblet" structure for commercial aircraft, something that the industry has been aspiring to for decades. This would be a quantum leap for civilian aviation in terms of fuel efficiency and environmental friendliness.