A Robust Rotorcraft Flight Control System Design Methodology Utilizing Quantitative Feedback Theory

This thesis describes application of digital multiple-input multiple- output (MIMO) Quantitative Feedback Theory (QFT) technique to the design of a three axis rate controller for the Lambda Unmanned Research Vehicle. The resulting robust controller performs well throughout the flight envelope without gain scheduling. It results from research done at the Air Force Institute of Technology. The Lambda URV was designed by the Control Systems Development Branch of the Wright Laboratory at Wright-Patterson AFB, OH for flight testing aircraft control hardware and software. The flight control system is built using a small perturbation linear model developed from flight test data. The actuators, also modelled from aircraft test data, are second order in roll and pitch and first order in yaw. Nineteen separate plants are used to represent the flight envelope of the aircraft resulting from variations in speed, altitude, center of gravity location, and weight. The sample rate is 50 Hertz. The pitch channel is decoupled from the lateral-directional resulting in a single-input single-output (SISO) system for the pitch channel and a two-by-two MIMO system for the lateral-directional channel. The design employs the Nichols Chart and is accomplished in the w'-domain.

Manual flight control system design for fighter aircraft is one of the most demanding problems in automatic control. Fighter aircraft dynamics generally have highly coupled uncertain and nonlinear dynamics. Multivariable control design techniques offer a solution to this problem. Robust Multivariable Flight Control provides the background, theory and examples for full envelope manual flight control system design. It gives a versatile framework for the application of advanced multivariable control theory to aircraft control problems. Two design case studies are presented for the manual flight control of lateral/directional axes of the VISTA-F-16 test vehicle and an F-18 trust vectoring system. They demonstrate the interplay between theory and the physical features of the systems.

An investigation of the interface between the technical literature's theoretical results and the problems that practising engineers face - and that engineering students will face - every day on the job. It demonstrates the extensive applications of quantitative feedback theory and seeks to bridge the gap between theory and practice. The book contains a user's manual and QFT design program on CD-ROM, to provide faster, easier access to design applications.

This thesis describes the application of the multiple-input multiple- output (MIMO) Quantitative Feedback Theory (QFT) design technique to the design of a digital flight control system for the Lambda Unmanned Research Vehicle (URV). The QFT technique allows the synthesis of a control system which is robust in the presence of structured plant uncertainties. Uncertainties considered in this design are the aircraft's plant variation within the flight envelope and the effects of damage to aircraft control surfaces. Mathematical models of control surface failure effects on aircraft dynamics are derived and used to modify an existing small perturbation model of the Lambda. The QFT technique is applied to design a control system utilizing aircraft pitch rate, roll rate and sideslip angle as feedback variables. The inherent cross-coupling rejection qualities of QFT and an aileron-rudder interconnect are utilized to design a control system which results in a coordinated flight. An outer-loop autopilot is then designed around the QFT controller to further assist turn coordination. Sensor noise effects on aircraft states are also analyzed. Quantitative feedback theory, Flight control system, Aircraft damage.

In the current climate of increasing complexity and functional integration in all areas of engineering and technology, stability and control are becoming essential ingredients of engineering knowledge. Many of today’s products contain multiple engineering technologies, and what were once simple mechanical, hydraulic or pneumatic products now contain integrated electronics and sensors. Control theory reduces these widely varied technical components into their important dynamic characteristics, expressed as transfer functions, from which the subtleties of dynamic behaviours can be analyzed and understood. Stability and Control of Aircraft Systems is an easy-to-read and understand text that describes control theory using minimal mathematics. It focuses on simple rules, tools and methods for the analysis and testing of feedback control systems using real systems engineering design and development examples. Clarifies the design and development of feedback control systems Communicates the theory in an accessible manner that does not require the reader to have a strong mathematical background Illustrated throughout with figures and tables Stability and Control of Aircraft Systems provides both the seasoned engineer and the graduate with the know-how necessary to minimize problems with fielded systems in the area of operational performance.