Ludwig Prandtl (4 February 1875 – 15 August 1953) was a German fluid dynamicist, physicist and aerospace scientist. He was a pioneer in the development of rigorous systematic mathematical analyses which he used for underlying the science of aerodynamics, which have come to form the basis of the applied science of aeronautical engineering. In the 1920s he developed the mathematical basis for the fundamental principles of subsonic aerodynamics in particular; and in general up to and including transonic velocities. His studies identified the boundary layer, thin-airfoils, and lifting-line theories. The Prandtl number was named after him. Early years Prandtl was born in Freising, near Munich, on 4 February 1875. His mother suffered from a lengthy illness and, as a result, Ludwig spent more time with his father, a professor of engineering. His father also encouraged him to observe nature and think about his observations. Prandtl entered the Technische Hochschule Munich in 1894 and graduated with a Ph.D. under guidance of Professor August Foeppl in six years. His thesis was "On Tilting Phenomena, an Example of Unstable Elastic Equilibrium" (1900), His work at Munich had been in solid mechanics, and his first job was as an engineer designing factory equipment. There, he entered the field of fluid mechanics where he had to design a suction device. After an initial failure, he carried out some experiments, he came up with a new device that worked well and used less power than the one it replaced. Later years In 1901 Prandtl became a professor of fluid mechanics at the technical school in Hannover, later the Technical University Hannover and then the University of Hannover. It was here that he developed many of his most important theories. On August 8, 1904, he delivered a groundbreaking paper, Über Flüssigkeitsbewegung bei sehr kleiner Reibung (On the Motion of Fluids in Very Little Friction), at the Third International Mathematics Congress in Heidelberg. In this paper, he described the boundary layer and its importance for drag and streamlining. The paper also described flow separation as a result of the boundary layer, clearly explaining the concept of stall for the first time. Several of his students made attempts at closed-form solutions, but failed, and in the end the approximation contained in his original paper remains in widespread use. The effect of the paper was so great that Prandtl would succeed Hans Lorenz as director of the Institute for Technical