This paper presents the development process of an aircraft control law. The control law is designed using a two-degree-of-freedom (2DoF) structured H∞ loop-shaping approach. This method allows the reuse of controller structures required by certification procedures while directly including handling qualities and robust stability requirements in the optimization process. This strategy is employed to develop a Rate Command and Attitude Hold (RCAH) demand system aimed at satisfying longitudinal handling qualities. First, the stability of the open-loop model and its compliance with the handling qualities guidelines are evaluated. Then, the control law is designed, with a detailed description provided of the design specifications and their formulation in the context of H∞ control. Subsequently, the controller parameters are optimized to satisfy the design specifications and a closed-loop analysis is performed. Finally, a simulator flight testing campaign is conducted to experimentally validate the designed control law. It is shown that the aircraft equipped with the RCAH system achieves better handling quality ratings (HQRs) and more favorable pilot feedback, providing a substantial improvement over the bare airframe.@en

This research is aimed at developing a comprehensive approach for robust hypersonic vehicle (HV) control utilizing modern H∞ techniques. Initial focus is placed on subsonic flight condition to validate the framework and controller design in a relatively familiar field, for which the HV are not primarily optimized. A 6-degree-of-freedom non-linear model of the GHAME hypersonic vehicle was constructed in MATLAB/Simulink, incorporating tensor-based equations of motion and embedded parametric uncertainty in the aerodynamic coefficients. The linear short-period longitudinal dynamics were then extracted at multiple operating points. A controller of fixed structure was synthesized using multi-objective (multidisk) H∞ mixed-sensitivity techniques with various performance and robustness requirements covering the pitch moment coefficient parametric uncertainty domain. Additionally, the design is extended to handle variations in Mach number, altitude, and fuel mass around the trim point using a multi-model approach. A single, structured control system successfully stabilized, rejected input and output disturbances and provided reference tracking for the uncertain short-period models and met the robustness margin requirements for the entire grid. It was then tested on the non-linear model and successfully performed the same tasks under parameter variations across the flight point grid.@en

To gain more insight into the performance of state-of-the-art Static Output Feedback (SOF) controller synthesis methods for H-infinity control, quantitative comparisons are made between Lyapunov methods and well-known established non-smooth optimization methods, i.e. hinfstruct and HIFOO. Three methods were deemed to be the most promising to compete and were bundled into one toolbox named SOFHi. The algorithms were extended to incorporate structured SOF and a variant of SOFHi was proposed to significantly improve upon the computational efficiency of the original implementation. Extensive comparisons show that SOFHi was able to compete with the established non-smooth methods and even able to significantly outperform one of them. Lastly, an elaborate flight control benchmark example is given to showcase the effectiveness of the algorithms, which involves the design of a gain-scheduled normal acceleration Control Augmentation System (CAS) for the F-16 Fighting Falcon.@en

To evaluate the benefits of structured parametric robust H∞ control a synthesis using this method is completed on a non-linear highly agile aircraft, called the ADMIRE. A gain scheduled two stage feedback controller with a feed-forward was used to design a pitch rate control augmentation system (CAS). The first stage focused on disturbance rejection while providing sufficient margins, while the second stage focused on the performance of the system. To compare the effects of parametric robust H∞ control three sets of controllers where synthesized, one nominal with no parametric synthesis, one with only the feedback controller synthesized with it and finally one system with both. The results show a clear trade-off between robustness and performance. The controllers synthesized with parametric synthesis greatly decreases the effects of uncertainty in disturbance rejection and tracking allowing for a more robust design@en

This paper introduces a multi-objective design approach for an Attitude Command-Attitude Hold (ACAH) and vertical velocity flight control system for the MBB Bo-105 helicopter longitudinal model. The design employs a decentralized structured H∞ dynamic controller using a PI-based and feed-forward control architecture, similar to the PID-based architecture commonly used in rotorcraft flight control design. The proposed design methodology integrates multi-objective approaches within the framework of structured H∞ control design. The uncertain model verifies the controller’s performance under different flight configurations for a helicopter at 40 kts, using mu-analysis which assesses robustness against model uncertainties. The multi-objective approach is employed in the control design process to tune parameters that balance handling qualities with robustness and stability. The performance of the resulting flight control system is investigated and evaluated against the required closed-loop time/frequencydomain criteria, as defined by ADS-33. The resulting design achieves Level 1 handling qualities, for which the advantages and limitations of the proposed methodology are discussed. @en

Incremental Nonlinear Dynamic Inversion (INDI) has received substantial interest in the recent years as a nonlinear flight control law design methodology that features inherent robustness against bare airframe aerodynamic variations. However, systematic studies into the robust design benefits of INDI-based control over the classical divide-and-conquer philosophy have been scarce. To bridge this gap, this paper compares the setup of hybrid INDI with a standard industry benchmark that is based on two-degree-of-freedom gain-scheduled proportional-integral-derivative control. This is done on an architectural basis and in terms of achievable robust stability and performance levels with respect to a common set of design requirements. To this end, a non-smooth, multi-objective H_∞-synthesis algorithm is used that incorporates mixed parametric and dynamic uncertainties in the design objective and constraints. It is shown that close similarities exist between hybrid INDI design and gain-scheduled PID control, which leads to virtually equivalent robustness and performance outcomes in both linear time-invariant and linear time-varying contexts. It is therefore concluded that the main benefit of the hybrid INDI does not lie in improved robustness properties per se, but in the opportunity to perform modular robust design in an implicit model-following context. Specifically, this implies that the areas of flying qualities, robustness, and nonlinear implementation are directly visible and accessible in the control law structure.

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This paper proposes a Linear Parameter-Varying (LPV) controller design for the pitch channel dynamics of a new class of Long Range Guided Projectiles (LRGP). The grid-based approach is preferred since it provides advantages in terms of performance and conservatism. Differently from standard aerospace applications that limit the scheduling vector to the variation of the altitude and the Mach number, the investigated flight envelope is parameterized through a 3D grid, which includes the variation of the angle-of-attack, crucial for range optimization purposes. Thus, an extensive investigation of the grid design is required to minimize the computational complexity of the controller synthesis. The performances of the LPV controller are assessed by employing a nonlinear reference tracking simulation scenario.

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Promising results on LPV design have been recently proposed, concerning the modeling and control of missiles, rockets, and aircraft. However, very few investigations have been focused on the development of guided projectile applications. This paper presents a pure linear parameter varying (LPV) modeling and control design approach intended to improve the range capability of a new class of Long Range Guided Projectiles (LRGP). The investigated concept consists of an asymmetric 155 mm fin-stabilized projectile equipped with a reduced amount of control actuators and characterized by a predominant unstable behavior across the analyzed flight envelope. The main advantages of the LPV design in terms of guaranteed robustness and stability are compared to standard gain-scheduling-based linear time-invariant (LTI) control strategies. A nonlinear simulation scenario is performed in order to assess the reliability of a pure LPV autopilot design, based on the polytopic formulation, across the entire flight envelope, over a local modal control design related to a specific set of flight conditions.@en

This article covers the design of an L1-adaptive Incremental Nonlinear Dynamic Inversion (INDI) autopilot applied to the control of the ballistic trajectory of a 155mm dual-spin projectile supplied with a roll-decoupled course-correction fuze. Associated with a Zero Effort Miss guidance law, the discrete-time INDI baseline successfully controls the lateral load factors of the projectile, resulting in a ballistic dispersion reduced to metric precision. However, aerodynamic data for dual-spin projectiles are often not very accurate because they rely on simplified CFD simulation and time-consuming wind tunnel tests aren’t always possible. Therefore significant parametric uncertainties are present in the model. Even if INDI is a sensor-based control technique, this approach is still sensitive to model mismatch. For this reason, L1-adaptive control theory was used to compensate for the degraded inversion of the INDI autopilot under the presence of parametric uncertainties. Nonlinear simulation results show the interest of an L1-adaptive augmentation of an INDI autopilot where the performance of the autopilot is guaranteed under a large range of time-varying matched uncertainties@en

This article deals with the control design of a dual-spin projectile concept, characterized by highly nonlinear parameter-dependent and coupled dynamics, and subject to uncertainties and actuator saturations. An open-loop nonlinear model stemming from flight mechanics is first developed. It is subsequently linearized and decomposed into a linear parameter-varying system for the roll channel, and a quasi-linear parameter-varying system for the pitch/yaw channels. The obtained models are then used to design gain-scheduled H_∞ baseline autopilots, which do not take the saturations into account. As a major contribution of this paper, the saturation nonlinearities are addressed in a second step through anti-windup augmentation. Three anti-windup schemes are proposed, which are evaluated and compared through time-domain simulations and integral quadratic constraints analysis. Finally, complete guided flight scenarios involving a wind disturbance, perturbed launch conditions, or aerodynamic uncertainties, are analyzed by means of nonlinear Monte Carlo simulations to evaluate the improvements brought by the proposed anti-windup compensators.

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