I'm not talking about adding camber, I'm talking about a varying thickness along the chord. I don't believe that a plate, with or without camber, is the optimum section. What makes a plate a plate is the constant thickness along the chord.
banktoturn,
The same argument applies if you vary the thickness along the chord.
As the Re (and the wing chord) gets smaller, the air density and viscosity become more dominant factors to how the air behaves along the wing's surface.
As I mentioned before, when the air approaches the LE of a wing with a positive AOA, it starts sensing the high pressure under and the low pressure above and some of the air just below the LE manages to sneak over the top.
This causes the shifting of the stagnation point to a spot somewhat below the wing's LE. And even if this natural behaviour is not unique to airfoils that are flat and thin, it has a special significance at very low Re's with airfoils that are flat and thin.
As the air molecules hooks its way back around the LE and over the top, it rounds the shape as it goes, so the upper surface flow gets a long, curved path from the stagnation point to the wing's TE.
By varying the thickness along the chord you may spoil the airfoil at such a low Re.
