Details of the E 662 airfoil are contained in:

Eppler, Richard: Some New Airfoils. Science and Technology of Low
Speed and Motorless Flight, NASA CP-2085, Part I, 1979, pp. 131-153.

Because winglets influence the flow around the wing (three dimensional),
their relationship to the airfoil (two-dimensional) is indirect.
Winglets should improve the climb of the Grob 104 because they reduce
the induced drag, just as they do for essentially all restricted-span
sailplanes. The structural capabilities of the 104 wing are best
addressed by Grob.

Incidentally, of probably more importance to the Grob 104 (Speed Astir)
is the installation of turbulators on the upper surface (yes, upper
surface) of the wing forward of the flaps and ailerons. The turbulators
alleviate the significant laminar separation bubble that forms when the
control surfaces are deflected downward. The addition of turbulators
not only improves the performance but also the handling. The ship can
be thermalled with larger positive flap deflections and the previous
"hunting" in pitch is eliminated.

Dan Somers
Port Matilda, Pennsylvania, USA