It is advantageous and generally customary to refer the aerodynamic coefficients of a wing-fuselage system to the geometric quantities of the original wing. A summary of the aerodynamic coefficients of the wing has been given by Eq. (1-21). These definitions of the aerodynamic coefficients are applicable directly to the wing – fuselage system when the forces and moments of the wing-fuselage system are
substituted. The reference axes and the signs of forces and moments are shown in Fig. 1-6.
To convey a feeling for the magnitude of the interference effects on wing-fuselage systems, a few test results are given in Figs. 6-3 and 6-4. In Fig. 6-Зд the lift coefficient cL is shown plotted against the angle of attack a for a simple mid-wing system of a rectangular wing and an axisymmetric fuselage, and for the wing alone. In the range of moderate angles of attack, the fuselage does not noticeably affect the trend of the cL(a) curve. The coefficient of maximum lift cLmax, however, is markedly reduced by the fuselage. This can be understood by realizing that the flow about the wing of a mid-wing airplane is strongly disturbed by the fuselage, leading to premature flow separation. The lift coefficient c£, versus the pitching moment coefficient cM for the wing alone and the wing-fuselage system is plotted in Fig. 6-36. Here the fuselage causes a strong increase in the pitching-moment slope йсмІйс^. The inclined fuselage alone has a pitching moment that tends to turn it into a crosswind position (see Sec. 5-2-3), and this pitching moment obviously is greatly increased by the effect of the wing.
In Fig. 6-4, the rolling-moment coefficient cMx is plotted against the angle of
Figure 6-4 Rolling moment due to sideslip of a high-wing system and of the wing alone, from Moller; fuselage and wing of Fig. 6-3.
sideslip for a high-wing system also consisting of a rectangular wing and an axisymmetric fuselage. The difference between the trends of the curves cMx(j3) for the wing alone and for the wing-fuselage system is quite large. The effect of the fuselage of a high-wing airplane consists of a strong increase in the rolling moment due to sideslip дсМх/Ъ&. This effect is caused by the cross flow over the fuselage. The interference effects shown in Figs. 6-3 and 6-4 can be treated theoretically. Other interference problems, particularly those of the drag of wing-fuselage systems, are hardly accessible to theoretical determinations. Therefore, in these cases experimental studies are indispensible [11, 15].
Summary reports about the interactions between the wing and fuselage in incompressible, and to some extent in compressible flow, have been published by Wieselsberger , Muttray , Schlichting [39, 41], Ferrari , and Lawrence and Flax , as well as Ashley and Rodden . Surveys of the aerodynamics of slender bodies have been given bv Adams and Sears  and Gersten