Impact of CCV Requirements on Flight Control System Design

Abstract

The advent of Controlled Configured Vehicle (CCV) design approaches has imposed severe reliability and fault tolerance requirements on aircraft flight control and supporting systems. This paper establishes the requirements for, and develops the configuration of, an integrated fly-by-wire (FBW) flight control system suitable for an unstable CCV fighter/attack aircraft design. The hydraulic and electric power systems are an integral part of the design problem, since their functions are essential to safety of flight. A three-channel FBW system configuration was chosen as optimum. The system features in-line monitored active/on-line secondary actuators, skewed rate gyros, triplex digital computers, accelerometers, and pilot input transducers. I. Introduction T HE advent of Controlled Configured Vehicle (CCV) design approaches has imposed severe reliability and fault-tolerance requirements on aircraft flight control and supporting systems. The objective of the study reported in this paper was to establish the requirements for, and to develop the configuration of, an integrated fly-by-wire (FBW) flight control system suitable for an unstable CCV fighter/attack aircraft design. The sensor, computer, and actuator subsystems were addressed, as well as the hydraulic and electric power sources. The hydraulic and electric power systems are an integral part of the design problem, since their functions are essential to safety of flight. Several advanced fighter/attack aircraft designs were examined to establish generic characteristics and mission requirements. A typical control surface complement was selected and multimode control law requirements were formulated. This enabled determination of the flight control system design requirements, including flight safety, mission reliability, and failure tolerance. The study approach was twofold. First, several design tradeoffs were performed to examine specific details of the system design for which the optimal approach was not well established. These investigations examined the following areas: 1) hydraulic system configuration, 2) electric power system configuration, 3) self-test/in-line monitoring considerations, and 4) command (secondary) actuator approach. Upon completion of the design tradeoffs, an overall FBW system configuration study was performed. It investigated redundancy requirements, cross-strapping/voting locations, and cost-weight-power tradeoffs. A significant aspect of this paper is that it examines the applicability of the various redundancy techniques to each subsystem of a FBW system. A blend of these techniques, different for each subsystem, was found to achieve the optimum FBW system configuration.