This paper continues previous work on the application of H _∞ Open Loop Shaping (OLS) to the design of thrust vector control (TVC) systems for launch vehicles (LVs). The contributions are threefold: first, further insight is provided into the selection and role of weighting filters within the loop shaping step; second, through two examples, it is shown that H _∞ OLS and H _∞ Closed Loop Shaping (CLS) result in equivalent controllers for rigid LVs, with neither approach outperforming the other; third, the H _∞ OLS methodology is extended to flexible LVs, introducing a simultaneous attitude controller and bending filter design strategy. Compared to H _∞ CLS, H _∞ OLS simplifies the design process by avoiding the simultaneous tuning of multiple closed loop transfer functions and ensuring robustness at the plant input and output. These advantages, combined with the demonstrated performance parity, support the use of H _∞ OLS for LV control applications. The flexible OLS framework was also benchmarked against the traditional separate design method, yielding similar results with reduced workload. Additionally, using the integrated approach in combination with a multi-model framework, a controller was developed and validated through linear simulations under both nominal and dispersed conditions, satisfying all TVC system performance and robustness requirements. Future work will address sloshing dynamics and develop a full-envelope controller for nonlinear simulation to further consolidate the methodology’s applicability.

The Generic Hypersonic Aerodynamics Model Example (GHAME) provides a practical benchmark for evaluating advanced control strategies for hypersonic vehicles. Its nonlinear dynamics and strong aero–propulsive coupling create challenges well suited to nonlinear inversion methods. This work develops a hierarchical control architecture based on time–scale separation, combining NDI for attitude and position control with Incremental Nonlinear Dynamic Inversion (INDI) for angular–rate and velocity control. The controller is implemented in MATLAB and Simulink and evaluated under synchronized and desynchronized sensor delays. The results show that delay synchronization markedly increases the admissible delay margin. The study also reveals a fundamental limitation in the lateral axis: the lateral-directional dynamics of GHAME are too fast to satisfy the time-scale separation assumption required by INDI, leading to unreliable linear stability predictions. In contrast, the longitudinal dynamics do satisfy this assumption and remain well suited to inversion-based control. Overall, the NDI–INDI structure is effective for the longitudinal motion when delays are synchronized, but the intrinsic speed of the lateral dynamics imposes a major constraint on its applicability for lateral control.

Nonlinear Dynamic Inversion (NDI) control and its Incremental variant (INDI) provide a conceptually simple and modular control framework, making it an attractive technique for designing flight control laws. By coupling these control architectures with robust control synthesis procedures, the overall approach can systematically ensure compliance with certification-level robustness requirements. In this sense, the H _∞ Loop-Shaping Design Procedure (LSDP) is a strong contender as a robust control synthesis approach, as it provides controllers with a priori robust stability guarantees. Therefore, in this study, structured H _∞ synthesis based on the H _∞ LSDP is used to systematize the development of (I)NDI control laws. This has been made possible by the advent of non-smooth non-convex multi-objective H _∞ optimization with MATLAB ^® systune. Despite the inherently nonlinear nature of (I)NDI-based control laws, local stability and robustness can be assessed using established trim-and-linearize techniques, allowing LTI methodologies to address design trade-offs in alignment with well established practices. Consequently, a linear hybrid Incremental Dynamic Inversion (IDI) control architecture is proposed, combining linear model-based DI with sensor-based IDI to leverage their complementary robustness properties. Model-following requirements are included using a weighting filter, whose parameters are optimized together with the hybrid IDI controller via a co-design approach. The potential of the proposed methodology is assessed in a design case study focused on a digital pitch-rate controller for a simulation model of NASA’s X-29 experimental aircraft. Results demonstrate that the synthesis procedure allows to optimize hybrid IDI controllers with the robustness guarantees associated with the H _∞ Loop-Shaping setup while simultaneously allowing to meet performance requirements.

The Flying V concept aircraft represents a notable candidate to reduce the carbon footprint of the aviation industry, with a potential 20% decrease in fuel use and a 17% higher lift-over-drag ratio. However, given the inherent design limitations concerning low control authority and pitch break-up tendencies, a well-designed control system is crucial for the aircraft’s safe operation. Thus, this study proposes a systematic design and tuning of a digital longitudinal flight control system that explicitly addresses robustness specifications a-priori. The flight dynamics simulation modeling is first detailed, followed by the outline and discussion of the design specifications. A C ^∗longitudinal control law is designed using a signal-based H _∞framework. Results indicate effective disturbance and noise rejection, stability under parametric uncertainties, Level 1 handling qualities, and satisfactory performance in the nonlinear model. These results validate the control law’s effectiveness, paving the way for future enhancements in gain-scheduled controllers for the Flying V.

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 μ-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.

Flight control system design for the Flying-V has been an active research area. However, despite the strengths of H₈ control, this framework has not yet been considered for the system design. Therefore, this study details the synthesis of a longitudinal control law using the robust control signal-based H₈ framework. The trimming procedure used to obtain operating points and linearized flight dynamics is explained, followed by a description of the design requirements which are systematically converted into hard constraints for synthesis. A structured controller design is conducted and the resulting system is evaluated in terms of performance and robustness in linear and nonlinear settings. Results indicate effective disturbance and noise rejection, stability under parametric uncertainties, Level 1 handling qualities predictions, and adequate performance. The C^* control law effectiveness paves the way for future enhancements in gain-scheduled robust controllers for the Flying-V and for the extension to lateral-directional designs.

Nonlinear Dynamic Inversion (NDI) has a long and successful history of research and development. The need for gain scheduling for nominal performance may be alleviated with the NDI method, which is accompanied by developmental benefits in terms of design modularity and transparency. However, the robustness of NDI-based control laws remains dependent on the nature of the open-loop plant. In this paper, a design and analysis framework based on quasi Linear Parameter-Varying (q-LPV) system theory is proposed that systematically considers this aspect across nonlinear operating regimes. The q-LPV model framework is presented in the context of robust hybrid incremental NDI control design, which incorporates inversion error compensation in addition to baseline model predictions. Based on a design case study for a simulated aeroservoelastic system, it is shown how systematic gain scheduling of the related inversion compensation design parameters can be performed with the proposed approach.

To gain more insight into the performance of state-of-the-art Static Output Feedback (SOF) controller synthesis methods for H _∞-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 SOF Hi. The algorithms were extended to incorporate structured SOF and a variant of SOF Hi was proposed to significantly improve upon the computational efficiency of the original implementation. Extensive comparisons show that SOF Hi 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.

In this paper, a linear parameter varying (LPV) modeling and control design approach is applied to a new class of guided projectiles, aiming to exploit the advantages of the LPV framework in terms of guaranteed stability and performance. The investigated concept consists of a planar symmetric 155 mm fin-stabilized projectile equipped with a reduced amount of control actuators and characterized by a predominantly unstable behavior across the analyzed flight envelope. A dedicated modeling procedure allows reformulating the nonlinear projectile dynamics as a LPV polytopic system, employed for the controller design. The procedure intends to reduce the computational complexity and the conservativeness affecting the overall controller synthesis. A trajectory-tracking simulation scenario is performed in a realistic simulator environment to assess the performance of the resulting LPV polytopic autopilot across the entire flight envelope.

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.

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.

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.