2.6 New markets Today, some 40 countries are export markets for Danish wind turbines, the largest being Germany, Spain, the United States, Italy, and Sweden. The background of the Danish turbine manufacturers was different from wind power companies in the U.S., Sweden, or Germany. Names like Boeing, Lockheed, Westinghouse, MBB, and Siemens indicate a strong background in aircraft and generator manufacturing. Interestingly, however, practically all of today's remaining larger wind turbine manufacturers have a machinery manufacturing background rather than an aircraft background. Although modern wind turbine technology resembles helicopter technology, the operating requirements are very different.
Wind turbines operate in fluctuating, relatively slowly moving air currents.
This makes it necessary to model aerodynamics in three dimensions rather than the two which are normally used in aircraft design. Aircraft designers, on the contrary, have to avoid the stall effect at all costs to prevent the aircraft from falling like a rock. Although modern wind turbines have borrowed a number of tools from classical aircraft design, including airfoil profiles, components are gradually becoming more specialised. The requirements for low noise emission requires special design of both rotor blades, gearboxes and other mechanical components. This design is known as the classical Danish concept, and tends to be a standard against which other concepts are evaluated.