Aeroelastic analysis of T-tails using an enhanced doublet lattice method

Abstract

The subsonic doublet lattice method is widely used to calculate unsteady air loads for aeroelastic analyses. Despite its widespread use and significant improvements in other aspects of the method, its application to the flutter analysis of T-tail aircraft is lagging in terms of accuracy and the efficiency of the process. In particular, the doublet lattice method does not calculate all the necessary aerodynamic loads for T-tail flutter analysis. It is common practice to calculate additional aerodynamic loads outside of the doublet lattice method and add them to the doublet lattice method results before solving the flutter equation. This paper describes the extension of the doublet lattice method to account for these loads. The boundary condition is made more general to account for yaw/dihedral and sideslip/dihedral coupling. The calculation of forces is generalized to account for lateral load due to roll and roll rate, rolling moment due to yaw, yaw rate and oscillatory sideslip, and yawing moment due to roll rate. In addition, the steady-state load and the quadratic mode shapes are taken into account in the calculation of generalized forces.