Maybe you got your answer already, but more information is always good.
"Polygon Stipple - This is a way of emulating or faking translucent shadows when the stencil buffer is turned off. It does this by creating a "dotted" effect that looks translucent (not unlike the stubble of incoming facial hair). Turn this off for a small performance boost. If stencil buffer and polygon stipple are both turned off, you'll get completely black shadows which isn't much of a drawback."
Does that describe the problem your having? I took the paragraph from the page below, and it helps explain the basic graphics settings...
Find out more about IL2 settings on this page of the "mission 4 today".
http://mission4today.com/index.php?n...p=show&kid=390