Introduction to Aircraft Aeroelasticity and Loads

18

Aircraft Internal Loads

So far, in Chapters 13 to 17, the different types of manoeuvre and gust inputs have been considered from the point of view of calculating the aircraft response in the rigid body and flexible mode generalized coordinates, and therefore potentially at any physical point on the structure. In this chapter, the way in which these responses are used to obtain the internal loads (i.e. moment, axial, shear and torque, or ‘MAST’, loads) at reference cross-sections in the airframe will be considered; the method of summation of forces is employed. The focus will be on the internal loads present in the main slender structural components of wing and fuselage.

Some important concepts of loads were introduced in Chapter 6 and it will be assumed that the reader has a grasp of these issues when reading this present chapter. In particular, the use of D'Alembert's principle to allow an accelerating member to be treated as being in effective static equilibrium by adding distributed inertia forces was considered. This approach is powerful in that it allows standard static methods of determining internal loads to be applied to an accelerating slender member subject to a loading which varies with time and is nonuniformly distributed spatially. Indeed, the airworthiness regulations (CA-25 and FAR-25) include direct reference to balancing the applied loads by inertia forces and couples. In Chapter 6, the slender members were considered as firstly continuous, and then represented ...