Tatoo, not to make fun of your quite nice flying airplane but it sure is ugly! Nothing personal and beauty is in the eye of the beholder and there is beauty in its functionality but ............ How could you possibly keep interest in that many wings on something that .... functional? Just kidding, just kidding...... maybe.

If you did a little rounding on the sharp corners and kept the undercambered aft part it is not all that different from the airfoils a lot of modern gliders are using. Ok maybe stretching it a bit but the undercamber does make a nice airfoil better for good upright work. It cannot be as good inverted since it is optimized for upright. It also depends on your criteria for determining what is good.

The inputs so far have been interesting to read. Pretty good stuff on this site. Almost makes me want to go back to work but not quite!

Years ago I designed a shoulder wing type configuration that had a diamond symmetrical airfoil about 10 percent thick. The planform was similar to the old UC Flight Streak and had coupled flaps-elevator for pitch work.

The airplane was too heavy to fly well butas a result of the weight had an interesting characteristic. When the angle of attack was pulled too high (actually not all that high) at a low speed the air flow would apparently separate. The airplane would pitch nose down since the tail airfoil was still attached and the airplane immediately started flying again.

In flight this looked like a longitudinal rocking motion along a level flight path. I changed the airfoil using the same lower surface and doubling the upper thickness ended up with a semi-diamond shape. Still with the sharp LE. The resulting airplane was nice to fly upright but not too good inverted. Still too heavy. It met its demise due to radio failure much too quickly to learn more.

Mostly it works down to pitch sensistivity is a function of CG location relative to the Neutral Point and elevator power (control throw and size). Light weight increases the airplane response to control inputs. Once you get past the basics and have a nice flying airplane then some small improvements can be made by optimizing the edge radius and wing thickness and those types of things.