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This paper deals with an integrated approach to predictive aircraft guidance and envelope protection applied to vertical flight path and airspeed control. The combination of discrete model-predictive control and dynamic trim method features into a constrained optimal guidance enabling envelope protection on a high automation level without limiting the basic systems performance. This approach offers a highly integrated solution optimizing the trade-off between high level flight management needs, low level basic flight control and aircraft performance constraints while maintaining the overall aircraft systems safety. The main topics addressed in this paper include 1) detailed introduction of the basic concept and its elements -discrete model predictive control, dynamic trim method and outer-loop-constraints approach -and 2) implementation and demonstration of the concept for longitudinal guidance in MATLAB R /SIMULINK R . Results obtained from various simulation runs have demonstrated the capability and feasibility of the proposed predictive flight guidance and envelope protection scheme.

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Flight testing on manned aircraft is expensive, since it requires, among others, certified aircraft, professional staff, and plenty of time and effort for preparation and postprocessing. Moreover, what, when, and how flight tests can be carried out is, in general, restricted by law or other regulations. To reduce the costs on flight test equipment and to lower regulatory requirements, unmanned, down-scaled research aircraft provide a reliable and cost-effective platform for technology demonstrations increasing the level of acceptance of novel concepts and methods on guidance, navigation, and control. The Unmanned Low-cost Testing and Research Aircraft (ULTRA) project, founded by the Institute of Aircraft Systems Engineering at the Hamburg University of Technology, enables such capabilities within a representative framework for research and testing adopting industry standard software and hardware components. An overview about the project objectives, the requirements, which led to specific design decisions, and the flight test platform itself are presented.

A parameter-varying, model-predictive envelope protection system is developed simplifying the controller structures required to keep the aircraft within a safe angle-of-attack and normal load factor envelope. The idea of a quasi-steady flight condition is used to map the flight envelope limits onto the setpoint values of a single flight control law. Since no mode switching is required, the selected level of automation, i.e., autopilot and flight management functionalities, is independent from the proximity to any angle-of-attack and normal load factor limit. In contrast to previous approaches, the proposed algorithm makes use of a quasi-linear, parameter-varying control loop model to adapt to the true nonlinear aircraft behavior. A variance-based sensitivity analysis highlights the most significant scheduling variables within this control loop model and, therefore, indicates the option of model reduction and improvement in efficiency, respectively. The proposed envelope protection system is evaluated throughout virtual flight tests with the unmanned flight test platform ULTRA-Dimona showing promising overall performance also in the presence of wind and turbulence. Keywords Envelope protection system Á Fixed-wing aircraft Á Linear, parameter-varying modeling Á Dynamic trim method Abbreviations ANOVA Analysis of variances CG Center of gravity DOE Design of experiments DT Dynamic trim LPV Linear, parameter-varying LTI Linear, time-invariant LTV Linear, time-varying MITL Model-in-the-loop q-LPV Quasi-linear, parameter-varying ULTRA Unmanned low-cost testing research aircraft