Longitudinal Dynamic Stability

Abstract

Abstract Longitudinal dynamic stability addresses the time history of motion following a disturbance in pitch. This chapter summarizes the most commonly used approach to analyze the two predominant longitudinal dynamic stability modes, usually referred to as the short period and phugoid. A review of the development of the six non‐linear aircraft equations of motion, along with a review of the three linearized longitudinal equations is a realistic prerequisite for the reader. A significant degree of importance is placed on obtaining excellent longitudinal dynamic stability characteristics in an aircraft design, with special emphasis on the short period mode, since the pilot's ability to accomplish tracking and maneuvering tasks is directly affected by these characteristics. In recent decades, baseline aircraft dynamic stability characteristics have been typically compromised in aircraft designs. This design compromise has been chosen in favor of decreased drag to obtain performance improvements such as increased range, endurance, and turning performance, with the knowledge that feedback control systems will be added to the design to “modify” the baseline dynamic stability and obtain excellent dynamic stability or handling quality characteristics.