Abstract: Composite structures may be formed using sheets of unidirectional fiber prepreg. Each of the prepreg sheets may include unidirectional fibers such as glass fibers and a binder such as plastic. The prepreg sheets may be wrapped around the outer surface of a drum. Ring-shaped sections of the wrapped sheets may be cut from the drum to form rings of prepreg layers. The prepreg rings may be placed into a mold cavity of a desired shape. While contained in stack of molds, prepreg rings may be cured by applying heat and pressure. Finished composite structures such as ring-shaped composite structures may be released from the molds following curing. The composite structures may be planar structures that have planar upper and lower surfaces and inner and outer edges. The fibers in the finished composite structures may run parallel to the upper and lower surfaces and parallel to the inner and outer edges.