As the aviation industry faces growing environmental and societal pressures, novel concepts such as the Flying-V emerge. Nevertheless, its unconventional configuration poses unique challenges in terms of stability and control, highlighting the pressing need for advanced control systems development. A gap in the literature arises concerning the lack of system robustness in the presence of uncertainties and the absence of robust controllers designed for the aircraft. Hence, the current study aims to increase the maturity of the flight control system of the Flying-V concept by implementing a C* longitudinal controller, while guaranteeing robustness stability and performance against uncertainty, adequate performance in the presence of disturbances and measurement noise, and compliance with Level 1 handling qualities. The Flying-V model is implemented in MATLAB/Simulink which served as the foundation for the controllers synthesis. Three designs are developed, which include a continuous time, a modified continuous time, and a modified continuous time multi-modeling controllers. These are conducted within the standard and signal-based H-infinity mixed sensitivity frameworks. Extensive analysis of the controllers is performed in terms of stability assessments, linear and nonlinear time domain simulations, and uncertainty sensitivity. Results demonstrate that the feedback of a combined signal demand such as the C* parameter provides, for a single input multiple-output system, a balanced disturbance rejection at the plant outputs. Conclusions are drawn in terms of the feedback controller structure, highlighting that high gain is necessary at low frequencies for disturbance rejection and roll-off at high frequencies allows control signal reduction and measurement noise attenuation. Moreover, taking into consideration the discretization effects of the flight computer in the design phase improves considerably the stability margins of the controllers. Lastly, it is verified that the proposed controller structures which are designed in the linear domain perform satisfactorily in the nonlinear simulation model and comply with the requirements defined. The multi-modeling controller proved successful in terms of robustness and performance across the flight envelope. Hence, we conclude that implementing this H-infinity optimization process for the design is a promising and viable method to guarantee robustness against uncertainties, disturbances, and measurement noise, as well as compliance with Level 1 HQ. The present work naturally paves the way for recommendations for future work. Some of these recommendations include the extension to lateral-directional control laws, gain-scheduling to guarantee the requirements across the flight envelope, maturity of the aerodynamic data, and pilot assessments of the handling qualities.

Power output during flight operation of multi-megawatt airborne wind energy systems is substantially affected by the mass of the airborne subsystem, resulting in power fluctuations. In this paper, an approach to control the tether force using the airborne subsystem is presented that improves the quality of the power output. This kite tether force control concept is implemented on the 3DOF dynamic simulation of the MegAWES reference model. First, the winch of MegAWES is resized because an analysis of winch inertia and radius shows its effect on power output and tether force overshoot. Second, the power consuming sections during the traction phase are eliminated by using a feedforward winch controller. Finally, the peak power is substantially reduced by implementing the kite tether force controller which uses a measurement of the tether force, angle of attack, and airspeed to keep the tether force constant when the system is at its power limit. This reduces the range between minimum and maximum power output by 75%.

Incremental Nonlinear Dynamics Inversion (INDI) flight controllers are sensor-based control systems, that are robust towards model uncertainty and with good disturbance rejection characteristics. These controllers show coupling effects in structural modes when implemented in specific flying vehicles with low-frequency structural motions. This paper investigates different INDI implementations, standard INDI, hybrid INDI, and notch filter placement in the INDI loop via simulation and flight tests on the Nederdrone. System identification of the structural characteristics of the vehicle and the system’s yaw dynamics are executed via ground vibration and hover flight tests. Closed-loop behaviour of theINDI inner-loop, disturbance rejection performance, and outer loop step-tracking performance was assessed with dedicated flight tests. The investigated INDI solutions show similar disturbance rejection and outer-loop step tracking performance, while the hybrid INDI solution performs a better nonlinear dynamic inversion.
Index Terms—INDI, complementary filter, unmanned vehicle, flight control system structural motion coupling

The increasing demand for sustainable aircraft solutions has encouraged the development of non-CO􁊼 emitting aircraft designs. Currently, a number of theoretically successful designs have been created by parties such as the Massachusetts Institute of Technology, National Aeronautics and Space Administration, and The Technical University of Delft. Unfortunately, these radical aircraft redesigns are too risky to conceive, requiring massive amounts of investment and research. Since growth of the global aviation industry will only persist if aircraft greenhouse gas emissions are reduced, airlines have been looking for more fuel efficient aircraft, and the demand for green solutions has skyrocketed1. Thus, in this study the A320appu is proposed in an effort to significantly decrease the environmental footprint of aviation while limiting the risks and cost that accompany novel designs. This is done trough a conversion of the A320neo to use a hybrid, multi-fuel power and propulsion system. By replacing the traditional kerosene Auxiliary Power Unit (APU) with a hydrogen engine and an aft mounted, boundary layer ingesting propulsor, the design will enter the narrow-body market as an intermediate step between current generation kerosene-powered aircraft and more distant radical redesigns, like the Flying V2 or the Aurora D8 3. The APU is thus adapted into an Auxiliary Power and Propulsion Unit (APPU). This single aisle, short-medium haul airliner was specifically chosen for this conversion because aircraft of this class are expected to comprise 80% of all aircraft sales by 2038. The reconfigured A320neo, coined the A320appu, shall provide an economically feasible and green alternative. It shall be the first advance towards normalising hydrogen within the aviation industry.

The challenges of designing the A320appu are to maintain low development costs, integrating the cutting edge subsystem and reassessing aircraft parameters such as the stability and controllability or range. Moreover the Operating Empty Weight (OEW) increases because of the added subsystems, and as the A320appu is designed for the same Maximum Take-off Weight (MTOW), the available payload decreases. The A320appu is designed such that the increase of the OEW is minimised, while maximising the integrability by limiting the amount of changes to the A320neo. Furthermore, significant reduction of the 𝐶𝑂􁊼 emissions and local pollution have to be ensured, while providing similar performance to the A320neo. To achieve the aforementioned points, four main changes to the A320neo are proposed below and thereafter discussed in more detail.

Incremental Nonlinear Dynamic Inversion (INDI) is a sensor-based control strategy, which has shown robustness against model uncertainties on various aerospace vehicles. The sensor-based nature of the method brings attractive properties which has made it popular in the last decade. INDI globally linearizes the system by making use of control input and state derivative feedback. The time lag between control input and state derivative is seen as one of the main challenges of the method. This has been partially solved by synchronization of actuator outputs with measurement, although the method is still vulnerable to unexpected measurement delays. This paper proposes Hybrid INDI approach to alleviate measurement delays and to reduce sensor dependence of INDI. The approach fuses the system model and sensor measurement via a complementary filter that produces angular acceleration estimation. The estimation responds fast to the system input thanks to the on-board model. It has also a low-frequency accuracy because of the sensor measurement. The method is found to retain good performance in case of model mismatches and measurement delays. An attitude controller is designed for the F-16 aircraft model and findings are verified with time-domain simulations.