Abstract
This paper presents the theoretical development of lifting surface theory for the calculation of aerodynamic airforce coefficients for cruciform-tail configurations. The cruciform tail is assumed to vibrate in simple harmonic motion in a subsonic airflow with small amplitude so that linearised aerodynamic theory is valid. Linearised integral equations are formulated that relate the normal velocities with the loadings on the lower and upper fins, and on the half-tailplanes. These integral equations are solved numerically for the loadings and then the generalised airforce coefficients when the cruciform tail oscillates at general frequencies in any antisymmetric mode. The configuration has a common junction chord and the condition is satisfied that the sum of the loadings at the junction is zero. Numerical results are compared with those obtained from Doublet-Lattice (NLRI) method and other theoretical methods wherever possible.