From Van's website:

"Two-seat RVs (the RV-9/9A excepted) use the proven NACA 230 series airfoil. These are turbulent flow airfoils with very low pitching moments. They do not require perfectly smooth surfaces to achieve good performance, so they remain almost unaffected by bugs and rain. The low pitching moment allows cruise trim drag to be kept to a minimum. The RV-9/9A uses a new Roncz airfoil design with a slightly longer wing span, shorter chord and slotted flaps for better low speed performance. The RV-10 uses a similar wing, but with a slightly different airfoil."

The GP .40 size RV-4 kit uses the Selig 8036 airfoil.

Mike