RE: Wing incidence degrees for a low wing monoplane?
The original Stahl plan has an airfoil 14% thick (Clark YM?) set at +3deg. per stab. at 0. This airfoil is 50% thicker than the normal Clark Y which would sit at 2deg. in the same position. Either is the correct relationship for pitch stability. The full scale plane had a high-mounted inverted engine like the PT-19. The thrust-line is above both the C.G. and the center of drag so should need no down-thrust, and with the high-drag air-foil shown would likely pitch down with added power. As is usual with these, the vertical stab. is high enough above the thrust-line to require some right-thrust to balance out.