sentences:  Theodorsen was the earliest to obtain reliable skin-friction drag data at subsonic, transonic, and supersonic speeds.After leaving NACA in 1946, Theodorsen helped organize and administer the Instituto Tecnológico de Aeronáutica (Aeronautical Institute of Technology) (1947–1950) in Brazil.Then he served as Chief Scientist for the U.S. Air Force from 1950 to 1954, during which time he did important work on the structure of turbulence.