The Effects of a Fuselage Upon the Stability of an Airplane

Abstract

THIS PAPER deals with the determination of fuselage moments and shows the change in moment as fineness ratio, depth, and width of fuselage are varied. In addition, the change in moments for a circular fuselage resulting from the interference effects of a wing can be found from the figures presented in the main body of the paper. The determination of the unstable moment of a body immersed in an in viscous, incompressible fluid can be made in terms of additional apparent mass coefficients. Coefficients of additional apparent mass have been calculated for a body of revolution by Lamb, and the unstable moment has been determined by Munk in term§ of these coefficients. O'Ponnell }n his doctor's dissertation has taken into account the variation of the additional apparent mass coefficients when the shape departs from a true prolate ellipsoid. Boundary layer effects were considered by Smith in the determination of the longitudinal additional apparent mass coefficient, and it was shown that the coefficient increased when the energy of the boundary layer was taken into account, Theoretic coefficients of additional apparent mass for an ellipsoid of three unequal axes are presented. In order to indicate the change in the theoretic coefficients wjien boundary layer, interference, and turbulence effeqts are considered, wind-tunnel tests on circular fuselages alone and in combination with a wing were used to determine the extent of the variation in the theoretic coefficients, An attempt has been made to give the necessary theory associated with the concept of additional apparent mass so that the reader may better understand the actual variation of moment of a body moving in a viscous fluid in terms of the mass coefficients.