A method of manufacturing a box for an airfoil having an outer skin, the method comprising: determining the location of a neutral axis of the airfoil box where compressive and tensile stresses are zero; forming a first unitary half-shell structure comprising a first portion of the skin of the airfoil, a plurality of stiffener members (34, 36) extending parallel to the first portion of the skin and configured to support the first portion of the skin, and a plurality of connection members defining connection flanges; forming a second unitary half-shell structure comprising a second portion of the skin of the airfoil, a plurality of stiffener members (54, 56) extending parallel to the second portion of the skin and configured to support the second portion of the skin, and a plurality of connection members defining connection flanges, each stiffener member of the second half-shell structure corresponding in position to a respective one of the stiffener members of the first half-shell structure, and each connection flange of the second half-shell structure corresponding in position to a respective one of the connection flanges of the first half-shell structure; and connecting each connection flange of the second half-shell structure to the corresponding connection flange of the first half-shell structure by disposing a plurality of fasteners through the corresponding connection flanges (42, 62) of the first and second half- shell structures, thereby forming the box with the first and second portions of the skin of the airfoil disposed in an opposing configuration and the stiffener members disposed there between, wherein the connection flanges (42, 62) are connected along a plane generally corresponding to the neutral axis. determining the location of a neutral axis of the airfoil box where compressive and tensile stresses are zero; forming a first unitary half-shell structure comprising a first portion of the skin of the airfoil, a plurality of stiffener members (34, 36) extending parallel to the first portion of the skin and configured to support the first portion of the skin, and a plurality of connection members defining connection flanges; forming a second unitary half-shell structure comprising a second portion of the skin of the airfoil, a plurality of stiffener members (54, 56) extending parallel to the second portion of the skin and configured to support the second portion of the skin, and a plurality of connection members defining connection flanges, each stiffener member of the second half-shell structure corresponding in position to a respective one of the stiffener members of the first half-shell structure, and each connection flange of the second half-shell structure corresponding in position to a respective one of the connection flanges of the first half-shell structure; and connecting each connection flange of the second half-shell structure to the corresponding connection flange of the first half-shell structure by disposing a plurality of fasteners through the corresponding connection flanges (42, 62) of the first and second half- shell structures, thereby forming the box with the first and second portions of the skin of the airfoil disposed in an opposing configuration and the stiffener members disposed there between, wherein the connection flanges (42, 62) are connected along a plane generally corresponding to the neutral axis.