The NACA Series of Airfoils
Beginning circa 1930, it was realized that there was a need to put the subject of airfoils on a rational basis. Accordingly, NACA designed and tested numerous airfoil shapes with systematic variations in camber and thickness. Airfoil shapes were generated by expressing various mean camber lines in mathematical – equation form and then wrapping different families of symmetrical thickness distributions around them. The resulting airfoils were tested experimentally in low-speed wind tunnels at different Re values, yielding force and moment data such as those shown in Fig. 5.3. Computer codes now are available that accurately predict pressure distribution, lift, and moment for these airfoil shapes. In a sense, it is now possible to perform the experiments on a computer. The benefit is lower cost and the capability to numerically optimize certain desirable characteristics.
Many of the NACA airfoils are still in use today, which is the result of the great care exerted in securing the airfoil data. We always can be sure that performance predictions based on these data are reliable. Each “family” of the NACA airfoils has a numbering system (explained herein).