A continuous composite structure manufacturing apparatus which comprises a conveyor (25) or conveyors for conveying one or more fabric webs (43) along a conveying path. Each of the webs (43) is comprised of a reinforcing fabric, a non-woven fabric, or a layered fabric. The fabric web (43) is passed through the conveyor (25) so that it defines an enclosed foam injection zone (37). A foam injection system is provided for injecting foam into the foam injection zone (37) to form a foam core preform or a plurality of foam core preforms. One or more dies (35) are positioned along the conveying path, to shape each of the foam core preforms to a desired cross-sectional profile. The individual stringers or multiple, spaced-apart stringers are produced concurrently in a continuous production process.