To produce the top aerodynamic efficiency from the laminar flow, an absolutely smooth surface was required. The engineers planned to paint and fill the wing surface to provide the necessary unvarying surface. The surface of the wing surface had to have an exceptionally smooth finish with less than .0005 of an inch surface roughness tolerated, and a maximum wave allowance was .0001 of an inch in any two inches of surface.13 Countersunk rivets, Dzus fasteners, secured panels while still providing a smooth surface.14
Figure 1. Wing Cross Sections15
7
During acceptance trials in Britain the aircraft was sprayed with a high-speed glossy paint finish to determine the actual effect of the finish when compared with a “standard” paint scheme. The lack of any discernible difference between the resulting flight performance using the two aircraft finishes surprised the engineers. It was concluded that the actual design and construction, especially the external smoothness could not be improved upon, and the design was especially aerodynamically “clean.”16
Arms and Armour Press, 1989), 31. 14 Robert W. Gruenhagen, Mustang: The Story of the P-51 Fighter, (New York: Arco Publishing, Inc., 1976), 43. 15 Alfred Price, Fighter Aircraft, Combat Development in World War Two, (London:
Arms and Armour Press, 1989), 31. 16 Ibid., 57.