The structure of a typical commercial aircraft is required to support two distinct classes of loads: the first, termed ground loads, include all loads encountered by the aircraft during movement or transportation on the ground such as taxiing, landing, or towing; while the second, air loads, comprise loads imposed on the structure during flight operations2.
The two above mentioned classes of loads may be further divided into surface forces which act upon the surface of the structure, e.g., aerodynamic forces and hydrostatic pressure, and body forces which act over the volume of the structure and are produced by gravitational and inertial effects, e.g., force due to gravity. Calculation of the distribution of aerodynamic pressure over the various surfaces of an aircraft’s wing was presented in Chapter 3.
Basically, all air loads are the different resultants of the corresponding pressure distributions over the surfaces of the skin produced during air operations. Generally, these resultants cause direct loads, bending, shear, and torsion in all parts of the structure.
2. In Chapter 7 we will examine in detail the calculation of ground and air loads for a variety of cases.