The underwater shark provides inspiration for green innovation in the sky as Lufthansa conducts surface tests
Patches being attached to an Airbus A340 (photo: Lufthansa Technik)
Thu 7 Feb 2013 – The first deliveries of new Airbus A320 aircraft fitted with Sharklet wingtip devices have started arriving at airlines. Airbus promises fuel burn and emissions reductions of up to four per cent and the manufacturer reports strong demand from customers for the Sharklet, an option on new A320 family aircraft and a standard fitting on the A320neo family, due to enter service in late 2015, which will contribute along with new-generation engines to an overall 15 per cent saving in fuel and reduction in CO2 emissions. Sharklets derive their name from the shape of a shark’s fin and the aerodynamics of the predatory animal have provided aerospace engineers with a further innovation to reduce aircraft drag. Airbus has joined forces with Lufthansa Technik and Fraunhofer IFAM to carry out a research project to harness the riblet effect in sharks on aircraft surfaces, and results so far indicate this technology could reduce fuel consumption by over one per cent.
Riblets are circumferential grooves in the scales a few micrometers in size that optimise the flow behaviour of certain shark species. The effect of these microscopically small grooves is to prevent any turbulence flowing at right angles to the direction of flow and so to reduce resistance.
This phenomenon has been known about for many decades but the aim of this experiment, conducted as part of the EU’s Clean Sky research initiative, is to transfer the known biological structures to corresponding technical processes. The two-year Multifunctional Coating project started in the summer of 2011 and now the partners are to test the durability of these surfaces in real-life flying operations. The idea, says Lufthansa Technik, is that the insights gained will show how resilient these structures are under the environmental influences encountered during flying operations and whether an economically viable service life can be demonstrated.
To obtain a reliable measurement, eight patches each 10 x 10 cm in size were attached to the fuselage and wings of two Lufthansa Airbus A340s, followed by the application of a special lacquer system that is hardened by ultraviolet light and is dirt-repellent, UV-stable and, thanks to nanotechnology, highly abrasion- and erosion-resistant. To apply the microstructured lacquer coating to the patches, a novel procedure that accurately transfers the microstructure to the lacquer, known as the ‘simultaneous stamp hardening method’, was developed.
If the tests now under way prove positive, the next stage will be to test larger patches before a highly automated application procedure is then developed. This could then lead to a highly accurate, fast and cost-effective procedure that allows the entire structure to be lacquered as if with a normal surface lacquer.