Half painted Fw 190 wing undersides - the purpose?

[CharlesMetz]

Originally Posted by Kari Lumppio

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Where my hypothesis in on weak ground is that on the underside there would be no need to smooth the surface further than some 10% from leading edge. The only other wing I know which also has this half-chord treatment is the P-51 Mustang.
--snip--

Kari,

One potentially relevant factor here is that the Mustang's wing was unusual in having a laminar-flow airfoil, the benefits of which were substantially reduced by any suface imperfections.