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Shark-based painted surface cuts aircraft drag

21st February 2013


Researchers from the Fraunhofer Institute have developed an innovative paint system that could improve the fuel efficiency of airplanes and ships by reducing their drag. The inspiration – and model – for the paint's structure comes from nature: the scales of fast-swimming sharks have evolved in a manner that significantly diminishes drag. The challenge was to apply this knowledge to a paint that could withstand the extreme demands of aviation: temperature fluctuations of -55 to +70 degrees C; intensive UV radiation; and high speeds. Yvonne Wilke, Dr Volkmar Stenzel and Manfred Peschka of the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research (IFAM) in Bremen, Germany, developed not only a paint that reduces aerodynamic drag, but also the associated manufacturing technology. In recognition of their achievement, the team has been awarded the 2010 Joseph von Fraunhofer Prize.
 
The paint features a sophisticated formulation, an integral part of which is nanoparticles that ensure the paint withstands UV radiation, temperature change and mechanical loads. Dr Stenzel explains: "Paint offers more advantages. It is applied as the outermost coating on the plane, so that no other layer of material is required. It adds no additional weight, and even when the airplane is stripped – about every five years the paint has to be completely removed and reapplied – no additional costs are incurred. In addition, it can be applied to complex three-dimensional surfaces without a problem."
 
Having formulated a suitable paint, the next step for the researchers was to clarify how it could be put to practical use on a production scale. Manfred Peschka says: "Our solution consisted of not applying the paint directly, but instead through a stencil." This gives the paint its sharkskin structure. The challenge was to apply the fluid paint evenly in a thin layer on the stencil, and at the same time ensure that it can again be detached from the base even after UV radiation, which is required for hardening.
 
When applied to every airplane every year throughout the world, the paint could save 4.48million tons of fuel. The benefits are also applicable to ships: the team was able to reduce wall friction by more than five per cent in a test with a ship construction testing facility. Extrapolated over one year, that means a potential savings of 2000 tons of fuel for a large container ship. With this application, however, there are additional complications, Yvonne Wilke explains: "One possibility exists in structuring the paint in such a way that fouling organisms cannot get a firm grasp and are simply washed away at high speeds, for example. The second option aims at integrating an anti-fouling element – which is incompatible for nature."
 
Irrespective of the fuel savings, there are even more interesting applications – for instance, with wind energy farms. Here as well, air resistance has a negative effect on the rotor blades. The new paint would improve the degree of efficiency of the systems.
 
For more information, visit www.fraunhofer.de






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