AERODYNAMICS OF THE WING – FUSELAGE SYSTEM
6- 1 INTRODUCTION
6- 1-1 General Remarks on the Interactions
among Parts of the Airplane
The aerodynamic coefficients of the major components of the airplane—wing, fuselage, empennage—are quite well established through theory and systematic measurements. The aerodynamics of the wing was treated thoroughly in Chaps. 2-4. The findings established there apply accordingly to the empennage (vertical stabilizer and rudder, and horizontal stabilizer and elevator; see Chap. 7). The aerodynamics of the fuselage was the subject of Chap. 5. When these individual parts are assembled into a complete airplane, however, their interaction (interference) plays a very important role in the formation of aerodynamic forces. In many cases these interference effects are of the same order of magnitude as the contributions of the individual parts to the aerodynamic forces of the airplane as a whole. For this reason, consideration of these interactions is indispensible to the study of the aerodynamics of the airplane. The physical processes behind the aerodynamics of the interactions, are, of course, much harder to conceive than those of the aerodynamics of the individual parts. Consequently, the theoretical study of the interference problem has been attacked much later and is, even today, not yet established to the extent of that of the individual parts. The theory of interference aerodynamics is available to a large extent for inviscid flow only.
Most important of the numerous interference effects among the various airplane components are the interactions between the wing and the fuselage and between the wing and the empennage. The interference between the wing and the fuselage is felt mainly in a changed lift distribution over these parts. The effect of the wing on the empennage, on the other hand, lies mainly in a changed incident flow direction of the empennage caused by the induced velocity field of the wing.
A further important interference effect is the so-called ground effect, which is created during flight near the ground. Hereby for equal lift, the lift slope is increased and the induced drag is usually reduced. This problem has been treated in detail in theory and experiment; see the references cited in Sec. 3-3-1.
In this chapter, only the interaction between wing and fuselage will be investigated. The interference problems related to the empennage will be treated in Chap. 7 together with the aerodynamics of the empennage.