airplane fuselage is circular or nearly circular rings called bulkheads. They are held in a position using stringers- lengths of wood or aluminum that lay over the edges of the frames. Then it is skinned in sheet aluminum.
same for models- using the idea of frames and stringers. models are often wrapped in heat shrinkable plastic. Old biplanes are wrapped in canvas. most modern planes are wrapped in aluminum alloy or carbon/ kevlar composite material.(fiberglass)