Manufacturing tolerances were off far enough, and maintenance of wing surfaces in the field were careless enough, that some significant points of aerodynamic similarity between the operational airfoil and the accurate, highly polished, and smooth test model were lost.
The record of this magnificent fighter plane confirmed expectations of appreciable improvements in speed and range as a result of the low-drag design, but practical experience with this and other aircraft using advanced NACA sections in the 1940s also showed that the airfoil did not perform as spectacularly in flight as in the laboratory. More than any other case study, the Mustang’s performance in the war demonstrates how the NACA’s laminar-flow airfoils proved to be a success, despite also being a failure. One of the major emphases of the documentary record is the experience of the North American P-51 Mustang, one of history’s most remarkable airplanes and the first aircraft to employ a NACA laminar-flow airfoil.