Aerodynamic modeling of an aircraft in atmospheric turbulence and correlation to hazard

Abstract

Improving aviation safety has become a focal point of present aeronautics research. Quantifying and predicting the hazards of flight into atmospheric turbulence is one area of interest. The present research investigates and extends the use of aerodynamic modeling techniques to better enhance the representation of nonlinear, unsteady effects in a turbulence encounter. The focus of the research is on flight dynamic, versus structural loads, aspects. Flight data from an intentional atmospheric turbulence penetration was used along with fuzzy logic techniques to develop and enhance longitudinal and lateral-directional aerodynamic coefficient models. These models indicated the presence of nonlinear and unsteady aerodynamic effects, including lateral-directional coupling into the longitudinal axis. Effective mass and damping were proposed as one means to correlate loads-induced hazards to the aerodynamic response of the aircraft, which were compared with results from an actual passenger flight. The results suggest that the cause of fast plunging motion may be shock-induced stall in largely static motion, i.e., low reduced frequency, whereas in oscillatory motion with higher reduced frequencies, dynamic stall may inhibit fast plunging motion. Therefore, some form of hazard index may relate to the magnitude of effective damping in plunging motion, or alternatively to the measure of unsteadiness in the aerodynamics of the encounter. A control strategy for countering a rapid plunge may benefit from means to artificially drive unsteady aerodynamic effects.