Structures and their Aeroelastic Manifestations

Though an airplane looks rigidly solid, in fact it is a surprisingly flexible machine. The loadings it experiences in flight can manifest themselves in a variety of ways that affect and "move” the structure, and, as dis­cussed previously, the flight control system itself can adversely affect the structure. The convoluted field in which aerodynamics and structures collide both statically and dynamically has led to some of the most com­plex and challenging problems that engineers, researchers, and design­ers have faced in the history of aeronautics.

The safety factor for a railroad bridge is usually "10,” meaning that the structural members are sized to carry 10 times the design load with­out failing. Since weight is so crucial to the performance of an airplane, however, its structural safety factor is typically "1.5,” that is, the struc­ture can fail if the loads are only 50 percent higher than the design value. As a result of the low aircraft design safety factor, aircraft structures receive far more attention during the design than do bridge structures and are subject to much larger deformations when loaded. This struc­tural deformation can also interact with the aerodynamics of an air­plane, both dynamically and statically, independently from the control system interaction mentioned earlier.