I imagine this subject has been somewhat hashed out on the forum from what I've seen, but here it goes. I've been looking into some airfoils for a design, but starting to confuse myself (not an aero guy). I have Riblett's book and was comparing his airfoil to the 6-series using Javafoil. I found the NACA 6 series to give some fairly good results (mainly cd vs cl; oldies but goodies?) while the Riblett results were a bit disappointing. Maybe it is how the software runs. It also showed much degraded results when you take away the cusp from the NACA foils which I understand is desirable for aileron forces. So, my questions: 1. Is a typical observation? 2. Is there a blended version between cusp and no cusp? 3. If I was going to spend real money on an airfoil analysis program, what would you recommend (VisualFoil, Profilli 2, DesignFoil)?