Standard Methods for Aerospace Stress Analysis

2Aircraft and Fuselage Stress Idealization

2.1 Introduction to Aircraft and Fuselage Geometry

Figure 2.1 shows the general arrangement of the primary structure of an aircraft, where skins, frames, longerons, and stringers come together to resist the applied loads to the aircraft. Other than aircraft skin, which resists the internal pressurization and the external loads, frames are used to support the aircraft skins. There are typically two types of frames: shear tie frames and floating frames. Shear tie frames transfer the shear loads from the frames to the skins. Also, floating frames, which do not have shear load transfer capabilities, are used to transfer the applied load in tension and bending to the skins. Refer to Figure 2.2 for shear‐tie and floating frame illustrations.

A typical wing construction configuration is shown in Figure 2.3. The wing consists of spars, ribs, stringers, and skins.

Most manufactured aircraft wing spars are made of solid extruded aluminum or aluminum extrusions riveted together to form the spar. Also, composite layups are used in the manufacturing and fabrication of wing spars. Figure 2.4 shows examples of metal wing spar cross sections. In an I‐beam spar, the top and bottom of the I‐beam are called the caps or flanges, and the vertical section in between the caps is called the web. The entire spar can be extruded from one piece of metal. Most times, it is built up from multiple extrusions or formed angles put together. The web acts as the principal ...