Electric Aircraft Dynamics

A Systems Engineering Approach

Ranjan Vepa

• Publisher: CRC Press
• Year: 2020
• eBook ISBN: 9780429514364
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Electric Aircraft Dynamics: A Systems Engineering Approach surveys engineering sciences that underpin the dynamics, control, monitoring, and design of electric propulsion systems for aircraft. It is structured to appeal to readers with a science and engineering background and is modular in format. The closely linked chapters present descriptive material and relevant mathematical modeling techniques. Taken as a whole, this ground-breaking text equips professional and student readers with a solid foundation for advanced work in this emerging field.

Key Features:

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• Provides the first systems-based overview of this emerging aerospace technology

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• Surveys low-weight battery technologies and their use in electric aircraft propulsion

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• Explores the design and use of plasma actuation for boundary layer and flow control

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• Considers the integrated design of electric motor-driven propellers

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• Includes PowerPoint slides for instructors using the text for classes

Dr. Ranjan Vepa earned his PhD in applied mechanics from Stanford University, California. He currently serves as a lecturer in the School of Engineering and Material Science, Queen Mary University of London, where he has also been the programme director of the Avionics Programme since 2001. Dr. Vepa is a member of the Royal Aeronautical Society, London; the Institution of Electrical and Electronic Engineers (IEEE), New York; a Fellow of the Higher Education Academy; a member of the Royal Institute of Navigation, London; and a chartered engineer.

1 Introduction

1.1 Introduction to Electric Aircraft

Ever-increasing energy demands and rising fuel prices have motivated aircraft industries to develop alternative power sources for future aircraft. In the aviation sector, the requirements of flight reliability, low noise-emission levels, reduction in the dependence on fossil fuels, requirements of lower costs and lower weight, and longer life cycles, increase the complexity of the overall system and lead manufacturers to introduce major breakthroughs and innovations. Hybrid electric propulsion and all-electric propulsion for future aircraft are currently popular fields in the aircraft industry and are forming the basis for future commercial aircraft designs. Hybrid electric propulsion systems are composed of a networked set of gas turbines and batteries, while in all-electric propulsion systems, batteries are the only source of propulsive power on aircraft. Current battery technologies pose the most serious limitations to the development of all-electric and more-electric aircraft. However, rapid strides are being made in the evolution of battery technology and, for this reason, most aircraft industries are planning to introduce either more-electric or all-electric powered aircraft within the next two decades. Electric aircraft will pose new problems related to general aircraft architecture, geometry and shape, battery, motor, and propulsion system design, aerodynamics, drag reduction and boundary layer control, aircraft performance, stability and control, the design of flight controllers, optimum structural design, and a host of other issues. In this book, we hope to bring together a number of current aspects of electric aircraft that are being extensively researched within the aerospace community.

The main goal of this book is to bring together the theoretical and design issues relevant to the field of electric aircraft and present the key topics on the most pressing problems that designers are facing in making electric aircraft more popular and commercially viable. It is also intended to identify the current state-of-the-art and new developments in the research on all-electric propulsion, hybrid electric propulsion and more-electric propulsion, as well as on the impact of the associated systems on all aspects of electric aircraft design.

1.2 The Systems Engineering Method

A “system” is an interacting combination of elements, viewed in relation to a function. A typical example of a system is an aircraft and, in our context, an electric aircraft. The elements or subsystems that make up the electric aircraft are the propulsion subsystem, the power storage system, the power supply systems, the power converters, the propeller, the lifting bodies and wings and the control surfaces which constitute the major elements that must be synergistically combined to produce an electric aircraft. Another example is the unmanned aerial vehicle (UAV) which again is composed of a host of subsystems which when assembled together perform holistically the functions of the UAV. These systems are, vehicle airframe structure and aerodynamics, propulsion, avionics systems, flight controls and high lift, flight management, mission management, fuel or power source management, environment control for avionics bays, hydraulic and/or pneumatic systems, electrical and power distribution systems, auxiliary and emergency power, recovery, communication and navigation, flight management/flight control, electronic flight information systems, recording and telemetry, landing gear, safety systems, built-in test equipment, maintenance and computing and software.

Systems engineering (SE) is an interdisciplinary field focusing on design and management of complex systems over their life cycle from a holistic perspective. Systems-thinking principles and modeling methods are used to organize this process. An SE approach ensures that all aspects of a project or system are being considered and included for an integrated solution. A variety of competences such as: requirements engineering, cross-disciplinary team coordination, testing and evaluation (V & V), reliability and maintainability (dependability) and topics from other disciplines are important when dealing with complex technological systems. When designing a new aircraft, there is a need to define the basic system at the overall system level. An example is,

The purpose of the aircraft is to carry 100 passengers and 1,000 kg of cargo a total distance of 400 miles at a Mach number of 0.2. The aircraft will operate primarily in sandy desert climates and at cruise altitudes of 10,000 to 15,000 ft.

Performance requirements establish how well a system or subsystem should perform, and constraints define the limits on the performance. They include broad specs: weight, maximum take-off weight (MTOW), center of gravity (CG) location, dimensions, reliability, safety and environment. At the subsystem level specification should contain some detail about its function and performance. For example, “The purpose of the subsystem is to protect the environmental control system from damage due to particulates in a sandy desert environment. The subsystem will remove at least 90% of the particulates from the air it receives.” In addition to function and performance, generally the statement should include parameters such as: weight, cost, electrical loads and air distribution.

Clearly one is dealing with a large system and it is essential to approach the study of such a large system, such as an electric aircraft, in a structured and systematic way. First and foremost, systems engineering requires a great deal of coordination across disciplines as there is a need to deal with a large number of possibilities for design trade-offs across subsystems. Faults arising from poor design can propagate across the subsystems and are generally difficult to predict. Moreover, the mutual lack of understanding across engineering disciplines can lead to several problems and in particular, the resistance to changes in design principles and practices that one has to introduce to cover technological changes that are expected in the future. Any engineer acts as a systems engineer when responsible for the design and implementation of a total system. The difference with “traditional engineering” lies primarily in the greater emphasis on defining the goals and decomposing the system into subsystems, creating and generating a number of alternative designs, evaluating all available alternative designs and then coordinating and controlling the diverse tasks that are necessary to create a complex system. The role of systems engineer is one of a manager who utilizes a structured value delivery process. Thus, the role of the systems engineer “is to define the system goals and the conditions under which the system must operate so that the designer is free to create the best system possible.” Systems engineering involves a process of systematic decomposition of the intended product or design into the subsystems and provides a balanced and disciplined approach to integration of the interacting component subsystems with the aim of delivering the synergistic goals of the system.

In the rest of this book, the systems engineering approach was adopted to decompose the overall electric aircraft into key subsystems so as to highlight and address some of the key technological challenges.

1.3 Hybrid and All-Electric Aircraft: Examples

Over a decade ago the Boeing company made history by showcasing a fuel-cell powered demonstrator aircraft [1]. A two-seat Dimona airplane, built by Diamond Aircraft Industries of Austria, was used as the airframe. With a 16.3 m wingspan, it was modified at Boeing’s European research laboratory to include a proton exchange membrane fuel cell/lithium-ion battery hybrid system to power an electric motor coupled to a conventional propeller. During the flights, which took place at the airfield in Ocana, Spain, pilot Cecilio Barberan climbed to an altitude of 3,300 ft (1,000 m) above sea level using a combination of battery power and power generated by hydrogen fuel cells. Then, after reaching the cruise altitude and disconnecting the batteries, Barberan maintained level flight at a speed of about 60 mph (100 kph) for 20 minutes on fuel-cell generated power alone.

A year earlier, an unmanned jet powered by hydrogen fuel-cell technology, the Hyfish (as it was named) had taken flight near Bern in Switzerland. It was a cooperative project between the German Aerospace Center, called the Deutsches Zentrum für Luft- und Raumfahrt or DLR in Stuttgart, Germany, and its international partners, including Horizon Fuel Cell Technologies of Singapore, culminating in the maiden flight of the Hyfish in 2007. Scientists at the DLR Institute for Technical Thermodynamics in Stuttgart integrated Horizon Fuel Cell Technologies’ ultra-light, compact fuel-cell system into this next-generation UAV, while keeping the total system weight to 13.2 lb. The Hyfish fuselage is about 4 ft long, and its wings are about 3 ft wide. During the flight, the UAV performed vertical climbs, loops and other aerial acrobatics at speeds reaching 124 mph, making the Hyfish the first fast plane with jet wings to fly with a hydrogen fuel cell as its only power source [2].

In November 2009, United Technologies Research Center (UTRC), the central research and innovation arm of United Technologies Corporation, achieved first flight of a hydrogen/air fuel cell powered rotorcraft. The successful technology demonstration was accomplished using a remote-controlled electric helicopter model modified to incorporate a custom proton exchange membrane (PEM) fuel cell power plant [3].

The power plant was a PEM fuel-cell prototype developed by the UTRC with a high-pressure hydrogen source and air were used. The self-sustained system with the power plant automatically started with the hydrogen supply and no additional batteries, and it was capable of carrying a 2.5 kg payload with a maximum output power of 1.75 kW and the system power density exceeded 500 W/kg.

In 2012, the use of efficient electric motors and batteries allowed pilots Bertrand Piccard and André Borschberg to keep the four-engine Solar Impulse aircraft aloft throughout the hours of darkness during a flight from Switzerland to Madrid that took 17 hours. After a change of pilot, the aircraft spent a further 19 hours in the air before landing in Morocco. The Solar Impulse has a wing span of 61 m, which is comparable with a commercial airliner, but at 1,500 kg the solar-powered plane weighs the same as a family car [4].

The first Airbus E-Fan prototype, which seats only one, was powered entirely by batteries. Powered by two lithium batteries, which provide 60 kW of power [5], the newer two-seater Airbus E-Fan prototype traveled from Lydd in Kent to Calais, France, a distance of 74 km, in 2015. With a wingspan of just under 10 m, the 600 kg aircraft was able to achieve speeds close to 200 km per hour at a cruising altitude of about 1,000 meters and managed to complete the journey in just 37 minutes [6].

The world’s first four-seat passenger aircraft powered by a zero-emission hydrogen fuel-cell propulsion, accomplished a successful first public flight in 2016. It took off from the airport in Stuttgart and successfully performed a short 15-minute flight [7].

These developments have spurred several aircraft design teams to redouble their efforts to design an all-electric civil passenger aircraft for the future. The development of electric automobiles has certainly given a boost to the design of a fully battery-powered all-electric aircraft.

1.4 Battery Power

The key to future all-electric flight is undoubtedly the limitations of current battery technologies. The use of batteries for electric power storage and to facilitate electric propulsion would signal a quantum leap toward the future and will gain commercial acceptance. Battery technology is already playing a key role in the development of electric cars. But to be useful in powering aircraft the energy density of current batteries must go up by a factor of ten. Innovative alternatives are being considered over segments of a typical flight which would require large amounts of power such as take-off and landing.

1.5 Range and Endurance of Electric Aircraft

Several studies have been conducted to maximize the range and endurance of electric aircraft. The problem is that electric aircraft cannot shed their weight as can a typical fossil fuel-powered aircraft and for this reason continues to maintain its weight right through the flight. Moreover, there is a need for fast-charging technologies, as well as technologies that would reduce the consumption of electric power during the take-off, cruise and landing phases of a typical flight by adopting optimizing strategies over all phases of a typical flight.

1.6 Propulsion Motors

The US National Aeronautics and Space Administration (NASA) has launched by far the most ambitious programs to help the development of electric propuls...

Table of contents

• Cover
• Half-Title
• Title
• Copyright
• Dedication
• Contents
• Preface
• Acronyms
• Chapter 1 Introduction
• Chapter 2 Electric Motors
• Chapter 3 Batteries
• Chapter 4 Permanent Magnet Motors and Halbach Arrays
• Chapter 5 Introduction to Boundary Layer Theory and Drag Reduction
• Chapter 6 Electric Aircraft Propeller Design
• Chapter 7 High Temperature Superconducting Motors
• Chapter 8 Aeroacoustics and Low Noise Design
• Chapter 9 Principles and Applications of Plasma Actuators
• Chapter 10 Photovoltaic Cells
• Chapter 11 Semiconductors and Power Electronics
• Chapter 12 Flight Control and Autonomous Operations
• Index