To lower the fuel consumption of airplanes and ships, it is necessary to reduce their flow resistance, or drag. A paint system from the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research IFAM makes this possible. Along with lowering costs, it also reduces CO2 emissions.
The inspiration and model for the paint's structure comes from the scales of fast-swimming sharks, which have evolved in a manner that significantly diminishes drag, or their resistance to the flow of currents. The challenge was to apply this knowledge to a paint that could withstand the extreme demands of aviation such as temperature fluctuations of -55 to +70 degrees Celsius, intensive UV radiation, and high speeds.
Yvonne Wilke, Dr. Volkmar Stenzel, and Manfred Peschka of the Fraunhofer Institute IFAM developed the paint that reduces aerodynamic drag as well as the associated manufacturing technology. Nanoparticles ensure that the paint withstands UV radiation, temperature change, and mechanical loads on an enduring basis.
"Paint offers more advantages," explains Dr. Volkmar Stenzel. "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."
"Our solution consisted of not applying the paint directly, but instead through a stencil," says Manfred Peschka. This gives the paint its sharkskin structure. The researchers had to apply the fluid paint evenly in a thin layer on the stencil, and ensure that it can again be detached from the base even after UV radiation, which is required for hardening.
If applied to every airplane every year throughout the world, the paint could save a volume of 4.48 million tons of fuel. The team was also able to reduce wall friction by more than five percent in a test with a ship construction testing facility. Extrapolated over one year, that means a potential savings of 2,000 tons of fuel for a large container ship.
With this application, the algae or muscles that attach to the hull of a ship only complicate things further. The researchers are working on two solutions for the problem. 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."
The paint system has other 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 – and thus the energy gain.