Enhancement of the Nonlinear OLOP-PIO-Criterion Regarding Phase-Compensated Rate Limiters

Abstract

The unique dynamic coupling effects between airframe, flight control system, and the pilot of modern, highly or super-augmented aircraft introduce new stability and handling qualities problems which do not occur on conventional airplanes. In particular, phenomena leading to a destabilization of the closed-loop system consisting of the airframe, the control and stability augmentation system, and the pilot, triggered by an undesired and unexpected interaction between pilot and augmented aircraft dynamics are known to be very dangerous for the aircraft and crew. They are commonly referred to as Pilot Involved or Pilot-In-the-Loop Oscillations. This paper focuses on the enhancement of the so called Open-Loop-Onset-Point-criterion, originally developed to predict PIO-susceptibility due to nonlinear effects such as position and non-phase-compensated rate limiting. The criterion is modified to also cover phase-compensated rate limiters, which are now commonly found in modern flight control systems.