Best Air foil for 1929 Primary glider

[jetmechord42]

I bought the plans for this glider from Ron Sands. His father drew the plans in 1978 .The air foil in the plans our out of date and the son recommend a Clark Y air foil .The EAA has some old 1930's books and list a Northrop glider ,which look almost the same as the1928 glider plan that Ron Sands sold me.The EAA 1930 book with the Nortthrop glider shows a U.S. 27 modified airfoil that gives higher lift at lower speeds. My question is their a better airfoil for this glider.

[Dana]

It's hard to go wrong with the Clark Y for a low speed aircraft, and its flat bottom makes construction and rigging relatively simple.