Abstract: A composite helicopter fuselage comprises at least one main frame member having two generally vertical side beams joined by generally horizontal top and bottom beams. Each side beam comprises a top hat section bonded to a filler material and the top and bottom beams each comprise two channel sections arranged back to back and bonded to a filler material. An area at each end of the top and bottom beams is devoid of filler and the top hat sections of the side beams are slotted between the channel sections, the parts then being joined by bonding the internal surfaces of the channel sections to the external surfaces of the top hat sections. The fuselage is completed by panels attached to the external flanges of the side and top and bottom beams.