CFD-based investigation of the aerodynamic characteristics of an aircraft emergency vertical tail

This study presents an exploratory two-dimensional CFD investigation of a backup vertical-tail concept for rudder-jam scenarios. The proposed configuration introduces retractable auxiliary vertical tails to the primary vertical stabilizer, enabling the generation of additional aerodynamic moment after deployment. Both the primary and backup vertical tails employ the NACA0012 airfoil, and the flow field is simulated using the Spalart–Allmaras turbulence model with a dynamic-mesh approach under a freestream condition of Mach 0.6. The analysis focuses on the evolution of the flow field and the resulting aerodynamic-moment behavior of the tail system under jammed-rudder conditions within an idealized two-dimensional framework. The results indicate that deployment and deflection of the backup vertical tail alter the pressure distribution and aerodynamic interactions between the tail components, resulting in significant variations in the computed aerodynamic moment. Under certain deflection ranges, the total aerodynamic moment of the modeled tail system exhibits zero crossings, indicating a compensatory aerodynamic-moment trend opposing the jam-induced moment. These findings provide mechanistic insight into how a backup vertical-tail configuration modifies the aerodynamic-moment characteristics of the vertical-tail system under rudder-jam conditions. Because the present study is conducted within an idealized two-dimensional framework, the results reflect qualitative aerodynamic trends and mechanisms and may serve as a basis for future three-dimensional investigations.