A wing or stabilizer (116, 118) of an aircraft, comprising: a box portion, comprising at least one spar and an outer skin coupled to the at least one spar; and at least one panel, comprising: an outer face-sheet, wherein in a fore-aft direction the outer face-sheet terminates at an outer free edge; an inner face-sheet having no portion in contact with said outer face-sheet at the leading end of the at least one panel, wherein in the fore-aft direction the inner face-sheet terminates at an inner free edge, said inner free edge being spaced apart from said outer free edge at the leading end of the at least one panel; and a core sandwiched between the outer face-sheet and the inner face-sheet; wherein: the inner face-sheet comprises a cantilevered portion; the cantilevered portion defines the inner free edge; the cantilevered portion is fastened to the outer skin of the box portion; and the inner face-sheet further comprises: a base portion; and a transition portion, between the base portion and the cantilevered portion; wherein a thickness of the base portion is less than a thickness of the cantilevered portion; and a thickness of the transition portion increases from the thickness of the base portion to the thickness of the cantilevered portion. a box portion, comprising at least one spar and an outer skin coupled to the at least one spar; and at least one panel, comprising: an outer face-sheet, wherein in a fore-aft direction the outer face-sheet terminates at an outer free edge; an inner face-sheet having no portion in contact with said outer face-sheet at the leading end of the at least one panel, wherein in the fore-aft direction the inner face-sheet terminates at an inner free edge, said inner free edge being spaced apart from said outer free edge at the leading end of the at least one panel; and a core sandwiched between the outer face-sheet and the inner face-sheet; an outer face-sheet, wherein in a fore-aft direction the outer face-sheet terminates at an outer free edge; an inner face-sheet having no portion in contact with said outer face-sheet at the leading end of the at least one panel, wherein in the fore-aft direction the inner face-sheet terminates at an inner free edge, said inner free edge being spaced apart from said outer free edge at the leading end of the at least one panel; and a core sandwiched between the outer face-sheet and the inner face-sheet; wherein: the inner face-sheet comprises a cantilevered portion; the cantilevered portion defines the inner free edge; the cantilevered portion is fastened to the outer skin of the box portion; and the inner face-sheet further comprises: a base portion; and a transition portion, between the base portion and the cantilevered portion; wherein a thickness of the base portion is less than a thickness of the cantilevered portion; and a thickness of the transition portion increases from the thickness of the base portion to the thickness of the cantilevered portion. the inner face-sheet comprises a cantilevered portion; the cantilevered portion defines the inner free edge; the cantilevered portion is fastened to the outer skin of the box portion; and the inner face-sheet further comprises: a base portion; and a transition portion, between the base portion and the cantilevered portion; wherein a thickness of the base portion is less than a thickness of the cantilevered portion; and a thickness of the transition portion increases from the thickness of the base portion to the thickness of the cantilevered portion. a base portion; and a transition portion, between the base portion and the cantilevered portion; wherein a thickness of the base portion is less than a thickness of the cantilevered portion; and a thickness of the transition portion increases from the thickness of the base portion to the thickness of the cantilevered portion.