This airfoil was designed around 1986. It has been used with great success in USA and England. As I told earlier it was an improvement over the Eppler 205 and they both have a flat belly from around 30% from the leading edge to the trailing edge. It’s a good airfoil for beginner models (the easy build part), and other models you want to be easy to build with fairly good aerodynamic efficiency. You do though loose some of the efficiency when choosing an airfoil with a geometric limitation (the flat bottom line). One of the more successful sailplanes with this airfoil was the Airtronics Legend (http://www.dchobby.com/short%20kit/legendfk.html). Dick Edmonds of Algebra fame also fell in love with this airfoil for some time. When looking at the polars you’ll get the feeling that it might be better than the SD 7037 in windy conditions (low Cl regions), but remember what Martin Simons once wrote about the experimental errors and don’t get overexcited about small differences in polars. Martin said that the experimental errors might get it to look the opposite way around when your sanding tool tortured wing takes to the sky.