Effect of Inverted V-Tail Size Reduction on the Aerodynamic Characteristics and Longitudinal Stability of a Small UAV

Abstract

This paper investigates the aerodynamic characteristics and longitudinal stability of an aircraft equipped with an inverted V-tail configuration, using numerical analysis in the context of preliminary aircraft design. The main goal is to study the effect of V-Tail size reduction on the aerodynamic and longitudinal stability performance.  The reduction in the modified configuration (tail span) was kept at 12.5 % of the original configuration. The study focuses on the evaluation of lift, drag, and pitching moment coefficients over a specified range of angles of attack under defined flight conditions. The analysis is conducted using the XFLR5 software as the primary computational tool, exploiting its three-dimensional flow analysis capabilities based on the Vortex Lattice Method and Lifting Line Theory to model the wing and tail and to examine the aerodynamic interaction between them. The numerical settings and simulation inputs are carefully defined to ensure result consistency and suitability for comparative analysis. The behavior of aerodynamic efficiency parameters and the pitching moment coefficient as functions of the angle of attack is analyzed. A comparison of the drag polar (C_L vs. C_D) and the lift-to-drag ratio (C_L /C_D) for both configurations reveals that the modified configuration achieves a maximum aerodynamic efficiency of approximately (C_L /C_D) max ≈ 29, which is comparable to, and slightly higher than, that of the original configuration. From longitudinal stability point of view, a comparison between the two configurations shows a relative convergence of the pitching moment curves for the modified case across different control surface deflection angles, compared to the original configuration with a reduction varying according to the corresponding deflection angle (maximum value 24%) in the pitching moment coefficient C_m.