Other bracing between the longerons and stringers can also  be used. Often referred to as web members, these additional  support pieces may be installed vertically or diagonally. It  must be noted that manufacturers use different nomenclature  to describe structural members. For example, there is often  little difference between some rings, frames, and formers.  One manufacturer may call the same type of brace a ring or  a frame. Manufacturer instructions and specifications for a  specific aircraft are the best guides. The semimonocoque fuselage is constructed primarily of alloys  of aluminum and magnesium, although steel and titanium are  sometimes found in areas of high temperatures. Individually,  not one of the aforementioned components is strong enough  to carry the loads imposed during flight and landing. But,  when combined, those components form a strong, rigid  framework. This is accomplished with gussets, rivets, nuts  and bolts, screws, and even friction stir welding. A gusset is  a type of connection bracket that adds strength.  [Figure 1-18]  To summarize, in semimonocoque fuselages, the strong,  heavy longerons hold the bulkheads and formers, and these,  in turn, hold the stringers, braces, web members, etc. All are  designed to be attached together and to the skin to achieve  the full-strength benefits of semimonocoque design. It is  important to recognize that the metal skin or covering carries  part of the load. The fuselage skin thickness can vary with the  load carried and the stresses sustained at a particular location.  The advantages of the semimonocoque fuselage are many.  The bulkheads, frames, stringers, and longerons facilitate the  design and construction of a streamlined fuselage that is both  rigid and strong. Spreading loads among these structures and  the skin means no single piece is failure critical. This means  that a semimonocoque fuselage, because of its stressed-skin  construction, may withstand considerable damage and still  be strong enough to hold together. Figure 1-18.  Gussets are used to increase strength. 1-10 Fuselages are generally constructed in two or more sections.  On small aircraft, they are generally made in two or three  sections, while larger aircraft may be made up of as many as  six sections or more before being assembled. Many aircraft are pressurized. This means that air is pumped  into the cabin after takeoff and a difference in pressure  between the air inside the cabin and the air outside the cabin is  established. This differential is regulated and maintained. In  this manner, enough oxygen is made available for passengers  to breathe normally and move around the cabin without  special equipment at high altitudes.  Pressurization causes significant stress on the fuselage  structure and adds to the complexity of design. In addition  to withstanding the difference in pressure between the air  inside and outside the cabin, cycling from unpressurized to  pressurized and back again each flight causes metal fatigue.  To deal with these impacts and the other stresses of flight,  nearly all pressurized aircraft are semimonocoque in design.  Pressurized fuselage structures undergo extensive periodic  inspections to ensure that any damage is discovered and  repaired. Repeated weakness or failure in an area of structure  may require that section of the fuselage be modified or  redesigned. Wings are airfoils that, when moved rapidly through the  air, create lift. They are built in many shapes and sizes.  Wing design can vary to provide certain desirable flight  characteristics. Control at various operating speeds, the  amount of lift generated, balance, and stability all change as  the shape of the wing is altered. Both the leading edge and  the trailing edge of the wing may be straight or curved, or  one edge may be straight and the other curved. One or both  edges may be tapered so that the wing is narrower at the tip  than at the root where it joins the fuselage. The wing tip may  be square, rounded, or even pointed.  Figure 1-19  shows a  number of typical wing leading and trailing edge shapes. The wings of an aircraft can be attached to the fuselage at  the top, mid-fuselage, or at the bottom. They may extend  perpendicular to the horizontal plane of the fuselage or can  angle up or down slightly. This angle is known as the wing  dihedral. The dihedral angle affects the lateral stability of  the aircraft.  Figure 1-20  shows some common wing attach  points and dihedral angle. Wing Configurations Wings Pressurization 