Automatic Flight Control Systems

The stiffness of an actuator depends on the closed-loop position control (architecture and parameters), on the load frequency, and, for fault-tolerant actuators, on the operative mode. The stiffness response is of basic importance for the design of actuators for primary flight controls, especially for high-performance aircrafts. Actually, in-flight conditions characterized by high speed and high angle-of-attack, the dynamic interactions between aircraft structure, actuator, and aerodynamic loads can induce aeroservoelastic effects, which, if not controlled, can imply performance degradation and even instability. The study and the compensation of such concerns require the assessment of the resonant frequencies of the aeroservoelastic system, which can be performed only by characterizing the dynamic stiffness of the actuator. This article reports the experimental activities carried out for the characterization of the stiffness response of a fault-tolerant fly-by-wire actuator for the primary flight controls of a modern jet trainer, starting from the feasibility studies of the experiments up to the execution of the vibration tests. The actuator stiffness performance is evaluated in different fail-operative modes by artificially injecting hydraulic and electrical failures, and the experimental data are interpreted by means of an LTI model of the flight actuator, highlighting and discussing the effects that the failures induce on the stiffness performance.

The current paper deals with the study of the electrical failures in fault-tolerant flight actuators, with particular reference to the short circuits of the servovalve coils. A highfidelity model of the servovalve of a modern fly-by-wire actuator is developed and validated through experiments, focusing attention on the characterization of the component dynamics in case of partial and total short circuits of the direct-drive motor coils. The servovalve model is then used to simulate a typical on-ground built-in-test procedure to determine the limit condition for the detection of a partial short circuit. Finally, once different possible combinations of short circuits are injected, the degradation of performances of the whole actuator is characterized through experiments, and the servovalve model is used to justify the test results, highlighting and discussing the effects of the failures on the system dynamics.

In an era of significant air traffic expansion characterised by a rising congestion of the radiofrequency spectrum and a widespread introduction of Unmanned Aircraft Systems (UAS), Global Navigation Satellite Systems (GNSS) are being exposed to a variety of threats including signal interferences, adverse propagation effects and challenging platform-satellite relative dynamics. Thus, there is a need to characterize GNSS signal degradations and assess the effects of interfering sources on the performance of avionics GNSS receivers and augmentation systems used for an increasing number of mission-essential and safety-critical aviation tasks (e.g., experimental flight testing, flight inspection/certification of ground-based radio navigation aids, wide area navigation and precision approach). GNSS signal deteriorations typically occur due to antenna obscuration caused by natural and man-made obstructions present in the environment (e.g., elevated terrain and tall buildings when flying at low altitude) or by the aircraft itself during manoeuvring (e.g., aircraft wings and empennage masking the on-board GNSS antenna), ionospheric scintillation, Doppler shift, multipath, jamming and spurious satellite transmissions. Anyone of these phenomena can result in partial to total loss of tracking and possible tracking errors, depending on the severity of the effect and the receiver characteristics. After describing GNSS performance threats, the various augmentation strategies adopted in the Communication, Navigation, Surveillance/Air Traffic Management and Avionics (CNS+A) context are addressed in detail. GNSS augmentation can take many forms but all strategies share the same fundamental principle of providing supplementary information whose objective is improving the performance and/or trustworthiness of the system. Hence it is of paramount importance to consider the synergies offered by different augmentation strategies including Space Based Augmentation System (SBAS), Ground Based Augmentation System (GBAS), Aircraft Based Augmentation System (ABAS) and Receiver Autonomous Integrity Monitoring (RAIM). Furthermore, by employing multi-GNSS constellations and multi-sensor data fusion techniques, improvements in availability and continuity can be obtained. SBAS is designed to improve GNSS system integrity and accuracy for aircraft navigation and landing, while an alternative approach to GNSS augmentation is to transmit integrity and differential correction messages from ground-based augmentation systems (GBAS). In addition to existing space and ground based augmentation systems, GNSS augmentation may take the form of additional information being provided by other on-board avionics systems, such as in ABAS. As these on-board systems normally operate via separate principles than GNSS, they are not subject to the same sources of error or interference. Using suitable data link and data processing technologies on the ground, a certified ABAS capability could be a core element of a future GNSS Space-Ground-Aircraft Augmentation Network (SGAAN). Although current augmentation systems can provide significant improvement of GNSS navigation performance, a properly designed and flight-certified SGAAN could play a key role in trusted autonomous system and cyber-physical system applications such as UAS Sense-and-Avoid (SAA).

Autopilot systems for unmanned aerial vehicles
(UAVs) and aircrafts provide flight missions without
need of human input and make them more reliable and
efficient. The first step of designing an autopilot is a
stabilizer mode. Conventional autopilot systems have
inner and outer loops. Stabilizer is the inner loop for an
autopilot. In this paper designing an aircraft control
system ensures good performance and robustness that
allows control of roll, pitch and yaw angles will be
declared. Aircraft dynamics are used to design the model
of the control system in the MATLAB Simulink
environment. Using loop shaping method to achieve
stable and robust control system will be the strategy.
Generated controllers to find the most effective one are
embedded in the X-plane which is one of the realistic
simulations.

Purpose Aeronautic transport has an effective necessity of reducing fuel consumption and emissions to deliver efficiency and competitiveness driven by today commercial and legislative requirements. Actual aircraft configurations scenario allows envisaging the signs of a diffused technological maturity and they seem very near their limits. This scenario clearly shows the necessity of radical innovations with particular reference to propulsion systems and to aircraftarchitecture consequently. Methods This paper presents analyses and discusses a promising propulsive architecture based on an innovative nozzle, which allows realizing the selective adhesion of two impinging streams to two facing jets to two facing Coanda surfaces. This propulsion system is known with the acronym ACHEON (Aerial Coanda High Efficiency Orienting Nozzle). This paper investigates how the application of an all-electric ACHEONs propulsion system to a very traditional commuter aircraft can improve its relevant performances. This paper considers the constraints imposed by current state-of-the-art electric motors, drives, storage and conversion systems in terms of both power/energy density and performance and considers two different aircraft configurations: one using battery only and one adopting a more sophisticated hybrid cogeneration. The necessity of producing a very solid analysis has forced to limit the deflection of the jet in a very conservative range (±15°) with respect to the horizontal. This range can be surely produced also by not optimal configurations and allow minimizing the use of DBD. From the study of general flight dynamics equations of the aircraft in two-dimensional form it has been possible to determine with a high level of accuracy the advantages that ACHEON brings in terms of reduced stall speed and of reduced takeoff and landing distances. Additionally, it includes an effective energy analysis focusing on the efficiency and environmental advantages of the electric ACHEON based propulsion by assuming the today industrial grade high capacity batteries with a power density of 207 Wh/kg. Results It has been clearly demonstrated that a short flight could be possible adopting battery energy storage, and longer duration could be possible by adopting a more sophisticated cogeneration system, which is based on cogeneration from a well-known turboprop, which is mostly used in helicopter propulsion. This electric generation system can be empowered by recovering the heat and using it to increase the temperature of the jet. It is possible to transfer this considerable amount of heat to the jet by convection and direct fluid mixing. In this way, it is possible to increase the energy of the jets of an amount that allows more than recover the pressure losses in the straitening section. In this case, it is then possible to demonstrate an adequate autonomy of flight and operative range of the aircraft. The proposed architecture, which is within the limits of the most conservative results obtained, demonstrates significant additional benefits for aircraft manoeuvrability. In conclusion, this paper has presented the implantation of ACHEON on well-known traditional aircraft, verifying the suitability and effectiveness of the proposed system both in terms of endurance with a cogeneration architecture and in terms of manoeuvrability. It has demonstrated the potential of the system in terms of both takeoff and landing space requirements. Conclusions This innovation opens interesting perspectives for the future implementation of this new vector and thrust propulsion system, especially in the area of greening the aero-nautic sector. It has also demonstrated that ACHEON has the potential of renovating completely a classic old aircraft configuration such as the one of Cessna 402.

The purpose of this document is to show evidence of the work carried out as part of the pre-flight flight validation activities of one RNAV approach Instrument Flight Procedures (IFP), down to LPV minima, at Katowice Airport (EPKT). The document is a deliverable of the TENT funded project " Support to the EGNOS APV Operational Implementation – APV MIELEC " .

This paper presents new efficient guidance algorithms allowing Unmanned Aircraft Systems (UAS) to avoid a variety of Global Navigation Satellite System (GNSS) continuity and integrity performance threats detected by an Aircraft Based Augmentation System (ABAS). In particular, the UAS guidance problem is formulated as an optimal control-based Multi-Objective Trajectory Optimization (MOTO) problem subject to suitable dynamic and geometric constraints. Direct transcription methods of the global orthogonal collocation (pseudospectral) family are exploited for the solution of the MOTO problem, generating optimal trajectories for curved GNSS approaches in real-time. Three degrees-of-freedom aircraft dynamics models and suitable GNSS satellite visibility models based on Global Positioning System (GPS) constellation ephemeris data are utilised in the MOTO solution algorithm. The performance of the proposed MOTO algorithm is evaluated in representative simulation case studies adopting the JAVELIN UAS as the reference platform. The paper focusses on descent and initial curved GNSS approach phases in a Terminal Maneuvering Area (TMA) scenario, where multiple manned/unmanned aircraft converge on the same short and curved final GNSS approach leg. The results show that the adoption of MOTO based on pseudospectral methods allows an efficient exploitation of ABAS model-predictive augmentation features in online GNSS guidance tasks, supporting the calculation of suitable arrival trajectories in 7 to 16 s using a normal PC.

An Aircraft Dynamics Model (ADM) augmentation scheme for Remotely Piloted Aircraft System (RPAS) navigation and guidance is presented. The proposed ADM virtual sensor is employed in the RPAS navigation system to enhance continuity and accuracy of positioning data in case of Global Navigation Satellite System (GNSS) data degradations/losses, and to improve attitude estimation by vision based sensors and Micro-Electromechanical System Inertial Measurement Unit (MEMS-IMU) sensors. The ADM virtual sensor is essentially a knowledge-based module that predicts RPAS flight dynamics (aircraft trajectory and attitude motion) by employing a rigid body 6-Degree of Freedom (6-DoF) model. Two possible schemes are studied for integration of the ADM module in the aircraft navigation system employing an Extended Kalman Filter (EKF) and an Unscented Kalman Filter (UKF). Additionally, the synergy between the navigation systems and an Avionics-Based Integrity Augmentation (ABIA) module is examined and a sensor-switching framework is proposed to maintain the Required Navigation Performance (RNP) in the event of single and multiple sensor degradations. The ADM performance is assessed through simulation of an RPAS in representative fight operations. Sensitivity analysis of the errors caused by perturbations in the input parameters of the aircraft dynamics is performed to demonstrate the robustness of the proposed approach. Results confirm that the ADM virtual sensor provides improved performance in terms of data accuracy/continuity, and an extension of solution validity time, especially when pre-filtered and employed in conjunction with a UKF.

We would like to invite you to join this exciting new project as a chapter contributor on one of the topics listed below. Since this is a textbook, a great deal of this chapter entails a survey on the topic under the paradigm of cyber-physical systems, what can be done onboard and remotely, the distributed nature of the system and some exercises on futurology (anticipating trends can shed some light on upcoming designs). IET will bring great visibility to your work. Each chapter should be around 20-25 pages each and can be submitted as a Word or Latex File. The IET will send you additional info (formatting, permission form, etc.) with the contributor's agreement once you have decided to contribute to the book. Visit http://www.theiet.org/resources/author-hub/books/index.cfm to get all contributor's information to an IET research-level book. Each book is expected to have a total number of 500 printed pages (with approximately 550 words per page and a 20% allowance for figures and tables). We have included a tentative schedule and list of topics below. If this is something you would consider, please send us the title of your chapter, a short description/abstract of the chapter content, and your full contact details. We will expect original content and new insights for this book. You can, of course, reuse published material but the percentage of material reuse for the chapter should be less than 40%. The IET will run a piracy software on the full manuscript to control that you are including original material and will reject chapters who contain a large amount of already-published material so please do take this into consideration. We would appreciate your feedback by December 31, 2017. Please do not hesitate to contact us if you have any queries. We look forward to working with you towards the successful publication.

A new computational technique based on Pseudospectral Discretisation (PSD) and adaptive bisection-constraint methods is proposed to solve multi-objective aircraft trajectory optimisation problems formulated as nonlinear optimal control problems. This technique is applicable to a variety of next-generation avionics and Air Traffic Management (ATM) Decision Support Systems (DSS) for strategic and tactical replanning operations. These include the future Flight Management Systems (FMS) and the 4-Dimensional Trajectory (4DT) planning and intent negotiation/validation tools envisaged by SESAR and NextGen for a global implementation. In particular, after describing the implemented PSD method, the adaptive bisection-constraint method is presented to allow an efficient solution of problems in which two or multiple performance indices are to be minimized simultaneously. Initial simulation case studies were performed adopting suitable aircraft dynamics models and addressing a classical vertical trajectory optimisation problem with two objectives simultaneously. Subsequently, a more advanced 4DT simulation case study is presented with a focus on representative ATM optimisation objectives in the Terminal Manoeuvring Area (TMA). The simulation results are analysed in-depth and corroborated by flight performance analysis, supporting the validity of the proposed computational techniques.

The innovative architecture of an advanced Flight Management
System (FMS) for Unmanned Reusable Space Vehicle (URSV) applications is presented with the associated re-entry trajectory
computation algorithm. The SL-12 unmanned space vehicle, developed by Cranfield University as a part of the 2012-2013 Aerospace Vehicle Design (AVD) Group Design Project (GDP) is used as the reference platform. The overall avionics architecture of the future space transportation vehicle is described. A detailed architecture is developed for the FMS and the core functions of such an FMS are described. A dedicated computation algorithm is presented for re-entry trajectory planning, which involves determination of the path of re-entry vehicle by means of angle of attack and bank angle modulation. Simulation case studies are performed in a realistic re-entry operational scenario resulting in the generation of efficient and feasible trajectories, without violating any of the defined constraints.

Flocking is a term that describes the behavior of a group of birds (a flock) in flight, or the swarming behavior of insects. This paper presents detailed information about how to use the flocking techniques to control a group of embedded controlled systems ''Boids'' such as ground systems (robotic vehicles/ swarm robots) in 2D and/or aerial systems (quadrotors) in 3D. Each one of these systems moves inside/outside of a building collectively to reach a target. This paper presents flocking behavior implemented on a server based control, which will process each of the boids properties e.g. position, speed & target. Subsequently the server will assign the appropriate move to a specific boid. The calculated information will be used locally to control and direct the movements/flocking for each boid in the group. A simulation technique and detailed flow chart is presented. In addition to the famous Reynolds' Rules for flocking two other rules are presented; one for targeting and another for avoiding obstacles. The targeting rule was implemented to ensure that the flock moves collectively towards a common target; it was implemented by creating a target velocity parameter. The avoiding obstacles rule was implemented to ensure that the flock doesn't collide with obstacles that they could be in the path; it was implemented by creating an avoiding velocity parameter.

The work deals with the design of the force control in a hydraulic workbench for primary flight actuators, to be used for hardware-in-the-loop simulations of a modern Fly-By-Wire Flight Control System. For this application, a high-bandwidth force response is needed in order to simulate aerodynamic loads on the control surfaces, but plant uncertainties can imply significant limitations. The variation of structural stiffness, due to hinge play and hinge local deformation, the uncertainties related to the flight actuator stiffness and the ones related to the hydraulic plant parameters lead to the necessity of a robust approach to the design of the force control. In the paper, a nominal LTI model of the plant is developed and the closed-loop force control is designed by means of a loop-shaping approach for different values of the bandwidth. The stability of the closed-loop force-controlled system is then verified by a robustness analysis, assuming the structural stiffness, the flight actuator stiffness, and some of the hydraulic plant characteristics as uncertain parameters. The
bandwidth of the force control is determined by finding an optimal compromise between dynamic performance and stability margin. Finally, in order to overcome the additional problems related to the flight actuator movements due to aircraft manoeuvres, a compensation feedback based on the flight actuator acceleration is proposed.

The availability of practical real-time models of primary flight actuators is a key aspect for performing hardware-in-the-loop simulations of fly-by-wire flight control systems. The solution could be offered by empirical models tuned on experimental data, but this approach would imply that hardware-in-the-loop simulations could be performed only after the actuators have been designed, constructed, and tested. The alternative approach, to which this work refers, is to develop high-fidelity actuator models based on the component physics and to reduce their complexity by trying to obtain a compromise between accuracy of results and real-time execution requirements. In the paper, real-time models of a servohydraulic actuator for primary flight controls are developed, taking into account the basic features of the fly-by-wire implementation (the non-linear direct-drive servovalve dynamics, the structural compliance, the oil compressibility, the saturation of commands, and the digital controls) as well as other physical phenomena, which are often disregarded in hydraulic actuator modelling (the hinge play, the flow forces on the servovalve spool, and the laminar servovalve flow). The simulation results of models characterized by different levels of complexity are compared with experimental data obtained by testing the aileron actuator of a modern fly-by-wire aircraft, and the relative importance of the model characteristics is highlighted and discussed, providing useful guidelines about actuator model reduction for realtime applications.

The present paper compares the effect of different waypoint parameters on the flight performance of a special autonomous indoor UAV (unmanned aerial vehicle) fusing ultrasonic, inertial, pressure and optical sensors for 3D positioning and controlling. The investigated parameters are the acceptance threshold for reaching a waypoint as well as the maximal waypoint step size or block size. The effect of these parameters on the flight time and accuracy of the flight path is investigated. Therefore the paper addresses how the acceptance threshold and step size influence the speed and accuracy of the autonomous flight and thus influence the performance of the presented autonomous quadrocopter under real indoor navigation circumstances. Furthermore the paper demonstrates a drawback of the standard potential field method for navigation of such autonomous quadrocopters and points to an improvement.