I have TurboCAD and obtained a number of airfoils in .dxf format. I superimposed the E193 airfoil on top of the S3021 airfoil and see that the rear upper section of the E193 has more height with a 'gentler' curve and that the high point on the E193 is further back on the airfoil. They are both 10 inch airfoils. I sort of feel that I would not really notice much of a difference between the two if flown on the same model but balanced appropriately (for each of the airfoils). Maybe the difference would be noticed in high speed flight between thermals (which would require faster flight with more high speed efficiency) and when working a thermal (slow, tighter circles).

My guess (and ONLY a guess) is that the S3021 would fly faster (with more efficiency) because of the thinner upper surface contour and that the E193 would work thermals better (light thermals for example) because of the gentler curve on the upper surface. Both have similar leading edges.

I am wondering how much of a visual difference would I have to SEE in the different airfoils before I would be able to DETECT a difference in performance in the air. And how much difference would there be in 'dead calm' cool air between the two airfoils mentioned.

I also overlayed the SD7037 and the S3021. They are very similar. Yet the SD7037 has become very popular in contest circles. It is hard to believe the very small difference I see in the airfoils can sway so many people away from one (S3021) and toward the other (SD7037).

I see the NACA2411 has a rather blunt leading edge and rather thick section but the E374 has a sharper leading edge. Both are almost the same thickness at the thickest point. I wonder where the E374 would excel and where the NACA2411 would excel.

Helpful, informative comments welcome.