Variable Stability In-Flight Simulation System Based on Existing Autopilot Hardware

A variable stability in-flight simulator has the capabilities to change the response of an aircraft in-flight, often without changing the physical properties of the aircraft. The ability to adjust the aircraft response characteristics and handling qualities has various purposes, such as pilot training, control system development, and handling quality research. A variable stability control system is designed for a medium-range business jet using incremental nonlinear dynamic inversion. The performance of the in-flight simulator is verified by two experiments, one conducted in a fixed-base flight simulator and one in a Cessna Citation II laboratory aircraft. The fly-by-wire actuation system in the Cessna Citation II is based on its existing autopilot, inheriting the limited performance and safety protections. The simulator experiment shows differences between the experienced handling qualities for a reference model and the designed controller combined with aircraft dynamics. These differences mainly arise due to actuator saturation for specific handling quality settings. The in-flight experiment supports the simulator findings but also reveals how the available control authority around the initial condition is limited due to constraints of the fly-by-wire system.