A shark learns to fly
Research project "FAMOS": System for the application of a sharkskin structure
The effect of sharkskin (riblet structure) has been known for almost four decades. Since then, many companies from a variety of industries have tried to harness the unique aerodynamic properties of sharkskin in the technical field. The aviation industry has been making similar attempts for quite some time as well. For instance, the European "Clean Sky" initiative did research on new, groundbreaking technologies that reduce the environmental impact of aviation. The aim of these long-term experiments was to transfer known biological structures to technical processes for the purpose of developing cleaner and quieter aircraft.
The "Multifunctional Coating" project conducted by Lufthansa Technik in cooperation with Airbus and the Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM) has already produced the first important results: During the research project, which ran from 2011 to 2013, the companies were able to develop new coatings and test the stability of sharkskin structures under real flight conditions. Small patches on the aircraft skin had previously confirmed the sustainable economic viability of this structure. Despite the microstructures showing a small amount of wear, the drag can still be reduced considerably.
During the follow-up project "FAMOS", Lufthansa Technik, the Fraunhofer Institute for Production Technology, Airbus Operations GmbH and bwm GmbH succeeded in developing an automated guidance system for the application of riblets on the skin of an aircraft. For this purpose, coating is first applied to a UV-transparent mold (matrix) comprising the negative of the riblets' shape. The negative mold is pressed into the fresh varnish, which is then hardened through UV light. When the negative mold is removed, the positive of the sharkskin remains on the surface. The matrix can take the form of an endless belt, thus making an automated process possible.
Painting takes place with the help of a mobile platform: A driver brings the platform into the desired working position and makes sure that it remains stationary. Subsequently, the riblets can be applied to the aircraft surface in strips – fully automatically. Each strip contains many parallel riblets running in the direction of application and parallel to the direction of air flow. While the riblets can be applied to all aircraft types, the research focused on A330, A340 and A350 long-haul aircraft. For the time being, the riblets will be applied to the upper side of the wings and the upper and lower sides of the horizontal stabilizer only. Other application surfaces, especially on the fuselage, are expected to follow.
Laboratory tests have confirmed the durability and efficiency of the sharkskin structure as well as the proper function of the prototype for the application head used to apply the sharkskin on the wing structure. If the process of industrialization and transition into production begins in the coming months, the automated coating of aircraft with drag-reducing sharkskin could become reality as early as 2019. Sharkskin surfaces would then enable airline operators to save around one and a half percent fuel for their fleets, thus reducing both costs and the environmental burden of the flights they operate.
The research project "FAMOS", an abbreviation of the German for "guidance system for the automated application of multifunctional surface structures", ran from September 2014 to June 2017. It was funded by the Federal Ministry for Economic Affairs and Energy (BMWi) as part of the aviation research program (LuFo V-1).