Aircraft Stability Characteristics in a Single Horizontal Tail Failure and Evaluation of Countermeasures for Safe Landing

This paper presents the stability characteristics of a high-speed aircraft in a possible emergency situation of a single horizontal tail failure during flight. The flight control system of the aircraft under study operates with a fail-safe mechanism where the malfunctioned horizontal tail is self-locked in neutral position, while the other tail can normally perform its operations. However, in such a scenario the aircraft is required to land at the nearest airfield on priority. Computational analysis is carried out to analyze the stability characteristics of the aircraft under this emergency where it is subjected to adverse pitching, rolling and yawing moments due to the locked horizontal tail. For computational analysis, a unique analysis technique is employed to isolate the horizontal tail geometry from aircraft and domain which helps in geometry/mesh consistency, even with different horizontal tail deflections. The results of baseline configuration are validated with literature and subsequently, the analysis is carried out at various flow conditions, horizontal tail deflections and ground clearances. A complete flight envelope is determined based on horizontal tail, ailerons and rudder deflection along with landing angle of attack for safe landing. The study can help in further improvement of the aircraft flight control computer to restrict the tail, aileron and rudder deflections up to the evaluated safe limits. Also, the designed methodology i2s applicable to all similar aircraft.