A robust suboptimal reentry guidance scheme is presented for a reusable launch vehicle using the recently developed, computationally efficient model predictive static programming. The formulation uses the nonlinear vehicle dynamics with a spherical and rotating Earth, hard constraints for desired terminal conditions, and an innovative cost function having several components with associated weighting factors that can account for path and control constraints in a soft constraint manner, thereby leading to smooth solutions of the guidance parameters. The proposed guidance essentially shapes the trajectory of the vehicle by computing the necessary angle of attack and bank angle that the vehicle should execute. The path constraints are the structural load constraint, thermal load constraint, bounds on the angle of attack, and bounds on the bank angle. In addition, the terminal constraints include the three-dimensional position and velocity vector components at the end of the reentry. Whereas the angle-of-attack command is generated directly, the bank angle command is generated by first generating the required heading angle history and then using it in a dynamic inversion loop considering the heading angle dynamics. Such a two-loop synthesis of bank angle leads to better management of the vehicle trajectory and avoids mathematical complexity as well. Moreover, all bank angle maneuvers have been confined to the middle of the trajectory and the vehicle ends the reentry segment with near-zero bank angle, which is quite desirable. It has also been demonstrated that the proposed guidance has sufficient robustness for state perturbations as well as parametric uncertainties in the model

Helicopters in tactical missions require superior handling and stability in turbulence. This paper proposes a sliding mode control (SMC)-based helicopter trajectory controller for enhanced handling qualities (HQs) with robustness to endogenous (modeling) and exogenous (turbulence) uncertainties. The flight control problem is posed as one of attitude, angular rate, and translational rate command tracking with closed-loop axial responses conforming to predicted level 1 HQs. The required closed-loop behavior is then enforced by a two-loop output-tracking SMC treating interaxis coupling and turbulence as matched, bounded uncertainties. To mitigate the chattering effect of SMC, a continuous control approximation using the boundary-layer concept is applied. The stability and tracking performance of the two-loop controller are analyzed. Furthermore, actuator saturations encountered during aggressive maneuvers are mitigated by reference command adaptation based on pseudo-control hedging. The proposed controller is evaluated against selected HQ temporal response criteria, two mission task elements requiring moderate to aggressive agility, and a shipboard approach in high-intensity turbulence. Simulation results highlight the controller’s trajectory tracking accuracy, adequate axial decoupling, and insensitivity to disturbances.

This letter synthesizes a C1 smooth, continuous, output-tracking sliding mode controller for a full-scale helicopter operating in high-intensity turbulence. The closed-loop dynamics are required to satisfy ideal on-axis attitude and rate response characteristics. Additionally, robust command tracking and suppression of off-axis responses are required in the presence of matched and unmatched uncertainties. Lyapunov based theoretical proofs are utilized for the tracking problem via application of a continuous second-order sliding mode (SOSM) controller. A second order sliding mode observer is employed to estimate the higher derivatives of the sliding variable for the output feedback controller. Simulations in hover illustrate the continuity, smoothness, and robustness properties of the proposed controller as compared to a conventional sliding mode controller and a linear quadratic controller.

Continued safe flight under all foreseeable scenarios will be crucial to assure airworthiness and build trust in future vertical takeoff and landing (VTOL) urban air mobility (UAM) concepts. Successful pilot intervention will be especially important for handling emergency procedures. This paper demonstrates the use of human-centric flight guidance concepts to mitigate the effects of non-catastrophic failures in future VTOL UAM aircraft. Specifically, a single failure in the lateral steering function of an automatic flight control system is considered. A new waypoint guidance law is proposed to generate the required roll command to manually steer the aircraft toward a predefined safe landing zone. Two display concepts are proposed to aid the manual execution of the roll steering command: a head-down display (HDD), and a head-mounted display (HMD). The guidance law and the display concepts were integrated into a high-fidelity, wide field-of-view rotorcraft simulation environment. Human-in-the-loop experiments were performed with non-pilot test subjects. The effectiveness of the guidance law and display concepts along with the associated piloting performance and human factor impacts were assessed. The results indicated that all test subjects were able to reach a close vicinity of the final waypoint. The HMD induced lower workload whereas the HDD resulted in better tracking performance.

Simulator experiments with pilots in the loop were used to identify the pilot model for helicopter in a roll tracking flight task. Experiments were conducted with several pilots with different flight experience levels, for several mission task elements with defined input forcing function as part of the commanded roll signal presented to the pilot visually. Variants of the mission task elements included two different displays, namely a primary flight display and a helmet mounted display. Another variation of the mission task elements was the inclusion of the pilot visual guidance algorithm that would bring the rotorcraft to the specified waypoint in an adaptive manner with respect to the current rotorcraft position. The frequency characteristics of the pilot model and pilot-vehicle system identified from the experiments were compared with the optimized pilot model for different variants of the mission task elements.