Card, during the good old days, when the model magazines were of some value, lots of construction articles and information about models in general, this was a popular subject. The airfoils that were recommended for model use were the Clark Y and NACA four digit ones. It was something gleaned from experience more than anything else. As the radios developed from single channel, where the Clark Y was heavily used, through reeds and then proportional, the more aerodynamic airfoils became popular, leading to the four digit use. They are still good for my type of flying. I am not interested in unlimited vertical performance, 3D, snap rolls or inverted low passes. Taking off and landing in one piece is all I’m looking for. I’ll attach two of my designs that appeared in the now defunct Flying Models magazine. They both used the NACA 2417. On sport models, where I don’t need the extra stability when landing, I use the 00XX airfoil. On the P26, I would recommend the NACA 2417 because of the plan form of the wing. Dan.
