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NASA Dryden conducted a handling qualities experiment using a small displacement centerstick controller that Saab-Scania developed for the JAS 39 Gripen aircraft. The centerstick, or ministick, was mounted in the rear cockpit of an F/A-18 aircraft. Production support flight control computers (PSFCC) provided a pilot-selectable research control system. The objectives for this experiment included determining whether the mechanical characteristics of the centerstick controller had any significant effect on the handling qualities of the F/A-18, and determining the usefulness of the PSFCCs for this kind of experiment. Five pilots evaluated closed-loop tracking tasks, including echelon and column formation flight and target following. Cooper-Harper ratings and pilot comments were collected for each maneuver. This paper describes the test system, including the PSFCCs, the Gripen centerstick, and the flight test experiment. The paper presents results of longitudinal handling qualities maneuvers, including low order equivalent systems, Neal-Smith, and controls anticipation parameter analyses. The experiment showed that, while the centerstick controller provided a different aircraft feel, few handling qualities deficiencies resulted. It also demonstrated that the PSFCCs were useful fo this kind of investigation.
The first flight test phase of the NASA Dryden Flight Research Center Autonomous Formation Flight project has successfully demonstrated precision autonomous station-keeping of an F/A-18 research airplane with a second F/A-18 airplane. Blended inertial navigation system (INS) and global positioning system (GPS) measurements have been communicated across an air-to-air telemetry link and used to compute relative-position estimates. A precision research formation autopilot onboard the trailing airplane controls lateral and vertical spacing while the leading airplane operates under production autopilot control. Four research autopilot gain sets have been designed and flight-tested, and each exceeds the project design requirement of steady-state tracking accuracy within 1 standard deviation of 10 ft.
Flight control design for modern fighter aircraft is a challenging task. Aircraft are dynamical systems, which naturally contain a variety of constraints and nonlinearities such as, e.g., maximum permissible load factor, angle of attack and control surface deflections. Taking these limitations into account in the design of control systems is becoming increasingly important as the performance and complexity of the aircraft is constantly increasing. The aeronautical industry has traditionally applied feedforward, anti-windup or similar techniques and different ad hoc engineering solutions to handle constraints on the aircraft. However these approaches often rely on engineering experience and insight rather than a theoretical foundation, and can often require a tremendous amount of time to tune. In this thesis we investigate model predictive control as an alternative design tool to handle the constraints that arises in the flight control design. We derive a simple reference tracking MPC algorithm for linear systems that build on the dual mode formulation with guaranteed stability and low complexity suitable for implementation in real time safety critical systems. To reduce the computational burden of nonlinear model predictive control we propose a method to handle the nonlinear constraints, using a set of dynamically generated local inner polytopic approximations. The main benefit of the proposed method is that while computationally cheap it still can guarantee recursive feasibility and convergence. An alternative to deriving MPC algorithms with guaranteed stability properties is to analyze the closed loop stability, post design. Here we focus on deriving a tool based on Mixed Integer Linear Programming for analysis of the closed loop stability and robust stability of linear systems controlled with MPC controllers. To test the performance of model predictive control for a real world example we design and implement a standard MPC controller in the development simulator for the JAS 39 Gripen aircraft at Saab Aeronautics. This part of the thesis focuses on practical and tuning aspects of designing MPC controllers for fighter aircraft. Finally we have compared the MPC design with an alternative approach to maneuver limiting using a command governor.
A study was conducted to design an experimental flight test program for the Total In-Flight Simulator CTIFS) directed toward the interface between flying qualities requirements and flight control system design criteria. The eventual goal is to provide an interpretation or translation of flying qualities requirements for use by the flight control system designer. Specifically, an angle of attack and pitch rate command system matrix involving both short term and long term dynamics are specified for evaluation. A major objective of the research was to demonstrate that flying qualities criteria and flight control system configuration or architecture can be independent. Finally, additional configurations are proposed to evaluate the efficacy of dynamic decoupling.