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Create side view sketch of the middle and bottom shell
Create a top view profile for the middle shell
Convert entities the middle shell profile into a new sketch
In a new sketch, Convert Entities the middle shell profile and then linear sketch pattern it downwards (2 inches), this creates the upper fillet reference
Add 2 points into the same sketch, where the upper fillet intersect with the bottom shell profile
Make a 3D sketch, and make a new point that is mated along X with one of the intersection points from the upper fillet sketch
Insert a reference plane that is defined by those 3 points
On this plane, draw a airfoil profile between the intersection points of the upper fillet and bottom shell profile