Washout angle vs wing incidence angle...

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I don't seem to find a graph or formula to get the wing change in incidence at root due to washout angle...
I'm about 7degrees wing root incidence on my design and planing on at least 2,6 degrees wash out on tip...
Am i supposed to add washout angle/2 to my root incidence?
Any help will be appreciated
thankz

PS: AR +3d effects +Ground effect where already taking into account for Wi.
Rectangular planoform none taper.

 

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