Development of a comprehensive PIO theory

Abstract

This paper outlines a comprehensive theory of pilot-induced oscillations (PIOs). PIOs can be divided into three convenient categories that are based on the nature of the pilot and vehicle dynamic behavior models and analysis techniques needed for their explanation. Category I PIOs are essentially linear; they can result from excessive lags in the effective vehicle, a mismatched pilot-aircraft interface, or shifts in pilot gain via command path gain shaping. Category II PIOs are quasi-linear, and are typically associated with rate-limiting. The sudden insertion of phase lags into the pilot-vehicle closed-loop system accompanying the onset of rate-limiting is one source of a flying qualities 'cliff'. Category III PIOs are fully nonlinear and nonstationary; they result from transitions in the effective vehicle dynamics or pilot behavior. These categories serve as points of departure for the study of simplified generic and specific examples that illustrate the nature and diverse sources of PIOs. Particular attention is paid to simplified system element characteristics that serve to qualitatively explain and approximately quantify key aspects of PIO phenomena. (Author)