Structural composite airfoils include a primary structural element and a secondary structural element defining the trailing edge of the structural composite airfoil. The primary structural element includes an upper skin panel, a lower skin panel, and a middle C-channel spar that is coupled to the upper skin panel and the lower skin panel. The upper skin panel extends from an upper leading edge end to an upper trailing edge end, and the lower skin panel extends from a lower leading edge end to a lower trailing edge end. The lower leading edge end of the lower skin panel is coupled to the upper leading edge end of the upper skin panel within the leading edge region of the primary structural element.