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Circulation Control (CC) by blowing over a rounded Coanda surface is capable of generating large lift forces while entraining the surrounding fluid. Its concept originates with Davidson in his 1960 British patent application. Within the sixties, CC was actively investigated for application on a high lift helicopter with elliptic rotors. The appeal of Circulation Control for high lift generation is its low blowing power required. However, supplying blowing air efficiently to the CC slot has proven to be an aerodynamic and structural engineering challenge. This delayed the first flight application of Circulation Control until a CC Technology Demonstrator STOL aircraft was completed in 1974. Elliptic airfoil based wings will not fly if blowing fails, so the airplane was designed with conventional wings. The engineering challenge was to provide in-flight transition from a rounded CC blown trailing edge to a conventional sharp trailing edge for low-drag cruise.