Flying Qualities for a Twin-Jet Transport in Severe Atmospheric Turbulence

Atmospheric turbulence is the leading cause of serious personal injuries in nonfatal accidents of commercial aircraft. One main type of motion that causes flight injuries in atmospheric turbulence is the sudden plunging motion with an abrupt change in altitude. To assess the possibility of designing a control system to mitigate such plunging motion, the dynamic stability characteristics must be known. The main objective of the present paper is to evaluate the dynamic stability characteristics and, more generally, the flying qualities of a twin-jet transport aircraft encountering severe atmospheric turbulence through digital six-degree-of-freedom flight simulations in transonic flight. The fuzzy-logic thrust model and unsteady aerodynamic models are used to estimate the nonlinear unsteady aerodynamics while performing numerical integration of flight dynamic equations. The flying qualities are based on the instantaneous eigenvalues of all flight modes obtained during time integration. It is shown that the real part of eigenvalues for the plunging mode (i.e., damping characteristics) is largely positive and can be used as a key parameter in describing the flying qualities in plunging.