Air traffic is experiencing a sustained growth since the last decades, provoking the saturation of the main air spaces in large areas of many countries. Moreover, air traffic is expected to increase even more in the upcoming years. In 2012, 9.5 million flights and 0.7 billion passengers were processed, but for 2035, 14.4 million flights with 1.4 billion passengers are expected (Eurocontrol,2016). In general terms, twice of today’s flight demand is expected over the next 20 years.
Therefore, it is a fact that current Air Traffic Management (ATM) infrastructure will not be able to support the growing demand unless refinements and enhancements are addressed towards an improved ATM service.
In consequence, research projects such as SESAR JU (Single European Sky ATM Re-search Joint Undertaking) and Next-Gen (Next Generation Air Transportation Sys-tem) are in charge of the development and deployment of the necessary items to build the world’s future air transportation system.
Among all the objectives encompassed within these projects, two main items seem pertinent:
1. Strategic datalink services for information sharing.
2. Negotiation between Air Traffic Control (ATC) constraints and aircraft prefer-ences in order to ensure an optimal use of airspace, while allowing aircraft to fly their preferred trajectories under the 4D guidance paradigm.
For this research work, the second point is of great interest.
Current Flight Guidance Systems (FGS) for transport aircraft operate in a mode-based logic, where the Flight Management System (FMS) switches different con-trol strategies (modes) to achieve specific concon-trol objectives. These concon-trol strategies are currently based on linear control theory, using either PID controllers, or State-Feedback linear approaches. However, since wind disturbances remain as one of the main causes of guidance errors, these guidance techniques need to be improved.
Therefore, the first objective of this research is to develop a nonlinear control strategy including both guidance and piloting loops, capable of taking into account wind dis-turbances, such that an enhanced tracking performance is achieved. Furthermore, considering that the approaches used to develop these guidance strategies rely on a numerical inversion of the aircraft model, better knowledge of the aircraft parame-ters is tough to improve the numerical inversion accuracy, and therefore, lead to a better guidance performance. In this work, the aircraft mass is considered a game-changer in terms of performance, such that a method to estimate this parameter is developed.
In addition to this, worldwide stakeholders are interested in flying their preferred routes. However, current ATC structure seems too rigid to support such action, and the unpredictability of aircraft operations eliminates the possibility of planning an
intended trajectory free of conflicts. In this way, with the view of increasing traffic safety and airspace capacity, the second objective of this manuscript is to provide a trajectory generation device able to better manage air traffic flows while meeting a set of flight profile constraints, which vary in general from flight to flight. The method proposed, should be able to address potential conflict resolution, allow air-craft to fly closer, and display the same functionalities of current flight planing de-vices.
Since the numerical feasibility of the presented approaches needs to be analyzed, the numerical simulation of a transport aircraft is needed. Thus, an important action of this thesis dissertation arises.
Stated this, the principal objectives of the thesis can be summarized in two items (O.1andO.2), along with two needed actions (A.1andA.2):
• O.1Development of a Trajectory Generation Algorithm valid for 4D Guidance.
• O.2Development of an Autopilot and a 4D Guidance Strategy for Transport Aircraft.
A.1 Numerical Simulation of a 6DOF Transport Aircraft.
A.2 Aircraft Mass Estimation.
In order to better present the efforts and findings towards the principal objectives of this research, the manuscript is organized as follows:
Chapter 2provides a panoramic vision of the current organization of Air traffic and its evolution towards the Trajectory-Based Operations paradigm, motivated by the expected growth of air traffic in the upcoming years and its related issues. This is crucial to understand the context that drives the contributions tackled in this re-search. Moreover, fundamental concepts such as the Performed-Based Navigation, Freeflight, and 4D operations are provided, all converging in the frame of SESAR and Next-Gen projects.
Chapter 3 introduces the flight dynamics of transport aircraft using the prin-cipal notation and reference frames. The rotational and translational motions are described by a set of nonlinear equations, which are presented in both a complete, and reduced form, taking into account wind contributions. Furthermore, notions of aerodynamics and load factor are given due to its relevance in other chapters.
The equations presented throughout the chapter establish the basis of flight analy-sis, since they represent the behavior of an aircraft during flight.
Chapter 4describes a numerical simulation of the presented flight dynamics us-ing Matlab, such that any theoretical proposition with regards to the aircraft motion is tested. Considering that many aerodynamic parameters are obtained via machine learning techniques, a background on this subject is presented, along with their par-ticular application in this work.
Chapter 5formulates a new method to generate trajectories valid for transport aircraft equipped with 4D guidance capabilities. These trajectories are meant to help in the transition from current ATC routes to Business trajectories, fulfilling safety constraints and helping to ease capacity issues and performance of guidance sys-tems. The smoothness and feasibility of the proposed trajectories is analyzed for different scenarios, where current FMS functions of modern aircraft are reproduced
Chapter 1. General Introduction 3 and optimized.
Chapter 6discusses the relevance of an accurate aircraft mass estimation for air-borne and ground systems performance, pointing out the lack of information and possible benefits regarding the knowledge of the aircraft mass. In consequence, a mass estimation method based on fuel consumption models is presented. The ap-proach considered is only analyzed during the climb phase, but its extension to a complete flight is straightforward. The algorithm also enables the computation of initial mass estimates, which increases its accuracy as more data becomes available.
In general terms, the aircraft mass estimation is conceived to complete the simula-tion of a transport aircraft, in order to ease the guidance efforts to follow a desired trajectory, considering that a better knowledge of the aircraft parameters leads to a better guidance performance.
Chapter 7delivers a sound background on linear and nonlinear systems, as well as linear and nonlinear control techniques. This serves as a basis for the proposition of guidance and autopilot methods. Moreover, the structure and operating princi-ple of flight control systems of modern transport aircraft is covered, where special attention is put on the lateral/vertical guidance modes, since they are encouraged to be substituted by up-to-date approaches.
Chapter 8presents two autopilots and two 4D guidance methods based on non-linear control theory. In this manner, having a time-parameterized trajectory to be followed, full 4D trajectory tracking is enabled by the use of any of the guidance algorithms along with any of the autopilots. This automation level is a milestone to-wards Trajectory-Based Operations. Furthermore, each autopilot controls different piloting variables, such that compatibility issues are addressed. In the same way, each guidance approach use different control inputs, such that compatibility issues with current guidance systems are also avoided. The advantages and drawbacks of each method are pointed out.
Chapter 9 is the final chapter of this research, such that a general conclusion and the potential improvements are provided. This chapter summarizes the efforts developed towards the transition from current organization of air traffic towards the future air transportation system, compliant with the new expectancies of Trajectory-Based Operations.
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