Early 1920's...

Till now, the development of Airfoils has been mostly entirely empirical. The development of airfoils gradually increased and led to a more systematic experimental approach. Many modern wing sections have been developed at GOTTINGEN during our first world war. Most of the wing sections which are developed at Gottingen are used even in the period of Second world war. During this period, National Advisory Committee for Aeronautics (NACA)  tested many families of wing sections in laboratories of various countries. This work by NACA was found to be very interesting and impressive. These investigations are systematized by  separation of the effects of camber and thickness distribution an experimental word very higher Reynolds numbers, experimental work was performed. These NACA wing sections are in common use till date. We can say that the work done by NACA was simply outstanding. First laminar flow airfoil sections are developed in 1939 by NACA. 

These airfoils produce a very low drag and the above shown airfoil has a lift to drag ratio of 300. Based on various parameters like thickness of the airfoil, maximum camber, maximum value of mean-line, NACA derived four-digit wing sections, five-digit wing wing sections, 1-series wing sections, 6-series wing sections, 7-series wing sections. These types of wing sections are found to be in interest even for today's aircraft manufactures.