Nonlinear Analysis of Aircraft Loss of Control

Abstract

Loss of control is a major factor in fatal aircraft accidents. Although definitions of loss of control remain vague in analytical terms, it is generally associated with flight outside of the normal flight envelope, with nonlinear influences, and with a significantly diminished capability of the pilot to control the aircraft. Primary sources of nonlinearity are the intrinsic nonlinear dynamics of the aircraft and the state and control constraints within which the aircraft must operate. This paper examines how these nonlinearities affect the ability to control the aircraft and how they may contribute to loss of control. Specifically, the ability to regulate an aircraft around stall points is considered, as is the question of how damage to control effectors impacts the capability to remain within an acceptable envelope and to maneuver within it. It is shown that, even when a sufficient set of steady motions exist, the ability to regulate around them or transition between them can be difficult and nonintuitive, particularly for impaired aircraft. Examples are provided using NASA’s generic transport model.