Full envelope multivariable control law synthesis for a high-performance test aircraft

Abstract

A full envelope multivariable flight control system is developed for the Variable Stability In-Flight Simulator Test Aircraft (VISTA). Separate control laws are designed for the longitudinal and lateral directional axes. Output feedback controllers with integral error feedback are created using linear quadratic synthesis and simple linear transformations. Longitudinal stick inputs are used to generate an angle-of-attack command at low-dynamic pressure and a normal acceleration command at high-dynamic pressure. Lateral stick inputs are used to generate a stability axis roll rate command, and rudder pedal inputs are used to generate a sideslip command. Linear point designs are integrated into a gain schedule to create a full envelope nonlinear control system. Flying qualities are evaluated according to military standards and shown to be satisfactory for a wide operating envelope. Classical gain and phase margins and analysis of the structured singular value show robustness to be acceptable for a wide operating envelope.