Robust autopilot design for aircraft with multiple lateral-axes controls using H∞ synthesis

The application of H_∞ control to the design of a lateral control system for an aircraft using conventional rudder and aileron controls as well as vertical canard control is considered. A linear time-invariant (LTI) model of the flight propulsion control coupling (FPCC) vehicle dynamics is chosen as an example. The design intent is to provide for decoupled response to yaw, path and roll commands. Results indicate that the H_∞ synthesis technique provides a powerful tool for the design of LTI multichannel controllers. Problem-specific design goals and constraints are reflected as weighting functions applied to closed-loop transfer functions in the problem formulation. It was shown that through the appropriate selection of closed-loop transfer functions (and weighting functions) it is possible to design for the steady-state accuracy, decoupled responses between command channels, closed-loop control bandwidth, restrictions on bandwidth, and tolerance to certain types of modeling uncertainty. The application of the approach to the FPCC aircraft yielded a design with robust performance and stability characteristics