Overview

Avionics systems are at the heart of modern military and civilian aircraft. The ability of these aircraft to operate safely and conduct their missions effectively relies heavily on the function and performance of their avionics systems. Functions such as automatic flight control, awareness of the aircraft and its surrounds, the ability to communicate using voice and data, and the need to accurately navigate across large distances, all rely on avionics systems. In most cases these days, avionics computers running specialised software provide avionics functionality. These computers are generally networked together to facilitate vast amounts of information sharing around the aircraft. At the beginning and end of the avionics chain is still the human operator called the pilot. The human machine interface (cockpit) has come a long way since aircraft started flying and it is still an area of huge change. Displays, tones, and interface devices continue to improve the efficiency with which information flows between the pilot and aircraft.

This book has been written to be help engineers, technicians, and aircrew understand how major avionics systems work and interact. The book is full of qualitative examples, case studies, and worked quantitative examples to reinforce the theory. Additional references at the end of each chapter allow readers to investigate individual topics in more detail. Review questions also allow readers to confirm their understanding of the main points in each chapter.

Chapter 1 is an introduction to avionics, Chapter 2 outlines aircraft electrical systems and Chapter 3 investigates flight control systems. Chapter 4 introduces air data, air-data sensors, and the air-data system, which is able to calculate a range of critical airspeeds, temperature and altitude. Continuing the theme of aircraft sensors, Chapter 5 discusses inertial sensors such as accelerometers and gyroscopes. Chapter 6 covers airborne radar systems. Chapter 7 is the final chapter on aircraft sensors and covers electro-optic sensors.

Chapter 8 deals with airborne communication systems. Chapter 9 is dedicated to airborne navigation, and is divided into two main sections; dead reckoning navigation and navigation by reference external navigation aids. Chapter 10 describes modern avionics systems as being a number of individual computers networked together. Chapter 11 explores some of the issues associated with running a number of time-critical applications on a single (or resource-limited) avionics computer. Chapter 12 is the final chapter of the book and covers the critical interface between the pilot and the aircraft; the cockpit. Chapter 12 also investigates image intensification in the form of night-vision goggles that are starting to play a major role in both military and civilian cockpits.

Ian Faulconbridge started his professional life as an electronics engineering officer in the Royal Australian Air Force. He was involved with maintenance activities and acquisition projects throughout his RAAF career. Since leaving the RAAF, he has been engaged as a professional engineer on a number of aviation-related consultancies. He has also taught avionics and navigation to undergraduate and postgraduate students at the University of New South Wales at the Australian Defence Force Academy.

Preface

Aircraft engines and airframes have traditionally dominated the function and performance of aircraft. Whilst these aspects are still major considerations in aircraft design and operation, the functionality of modern aircraft is increasingly provided by avionics systems, which provide critical functions such as automatic flight control, situational awareness, navigation, communications, and identification.

This book aims to provide a complete coverage of modern avionics systems in a structured fashion to support the work of professional engineers, technicians, and aircrew. The book has been written to allow engineers and other technical people to gain an appreciation and understanding of the discipline. Additional references are provided at the end of each chapter to support further reading and investigation as required. The structure of the book is such that it makes an ideal companion to flight manuals used by aircrew to understand their aircraft. Whilst flight manuals describe a particular aircraft and its systems, this book explores the avionics systems more generally and in more detail.

The book has also been written to support undergraduate education in avionics systems. As well as the references at the end of each chapter, each chapter also includes qualitative and quantitative review questions. These questions attempt to capture the main learning points from each chapter. Answers are provided to the quantitative questions. Worked examples and case studies throughout the text also allow students to reinforce their understanding of key areas.

Chapter 1 is an introduction to avionics. Major (non-avionics) systems are first described to place avionics into context with broader aircraft design. The major avionics systems and their primary functions are then described. Each of the following chapters investigates these avionics systems in more detail. Chapter 2 outlines aircraft electrical systems because avionics systems rely on electrical power to operate. The typical electrical outputs are described, as are the main standards used during the design of aircraft electrical systems. Some fundamental design philosophies leading to typical aircraft electrical systems are then investigated followed by some case studies. Chapter 3 investigates flight control systems. Most modern aircraft rely of avionics systems called flight control systems to perform critical functions like stability augmentation and autopilot. Chapter 4 introduces the concept of air data. By sensing atmospheric pressures and temperature, a system called the air-data system is able to calculate a range of critical airspeeds, temperature and altitude. This chapter describes the components of an air-data system and the calculations performed by an avionics computer called the air-data computer. Continuing the theme of aircraft sensors, Chapter 5 discusses inertial sensors such as accelerometers and gyroscopes. Both traditional mechanical gyroscopes and modern optical gyroscopes are described. The information provided by gyroscopes and accelerometers is a critical input into inertial navigation systems and attitude/heading reference systems discussed in later chapters.

Chapter 6 covers airborne radar systems, looking at the basics of pulse radar. The concepts of resolution and ambiguity are introduced before discussing antenna characteristics, receiver sensitivity, and radar cross section. The radar range equation is introduced as a way of determining the likely range performance of a given radar system. CW-FM radar altimeters and Doppler heading reference systems are described. A section is also dedicated to an important class of airborne radar called pulse Doppler radar. The chapter concludes with a worked example. Chapter 7 is the final chapter on aircraft sensors and covers electro-optic sensors. These sensors rely on energy in the optical portion of the spectrum. Examples of airborne electro-optic sensors are discussed and the major components of an electro-optic system described. The relevant laws of physics are described as the basis for a worked example on infrared detection. The well known AIM-9 air-to-air missile is used as a case study on an operational electro-optic system.

Chapter 8 deals with airborne communication systems and covers the basics of communications theory before discussing the various communications systems on-board a typical aircraft. The major components of a communication system, including aircraft antennas, are described. The need for data communication is also discussed and the Link-16 tactical data link is used as a case study. Associated issues including electromagnetic propagation and loss are detailed in this chapter. Chapter 9 is dedicated to airborne navigation. It is divided into two main sections; dead reckoning navigation and navigation by reference external navigation aids. Dead reckoning requires an appreciation of where the aircraft started its journey, the speed and direction of travel, and the duration of the travel. With this information, current location can be calculated. A number of sensors including inertial sensors, air data sensors, and radar sensors can provide the information required to perform dead reckoning navigation. Aircraft also use a number of navigation aids on the earth’s surface or in space to navigate. Possibly the most well known aid is GPS. This chapter also looks at NDB/ADF, VOR, DME, and TACAN. The ILS landing system is also described. Chapter 10 describes modern avionics systems as being a number of individual computers networked together. The options for networking airborne computers are explored and a case study of arguably the most prevalent airborne network, MIL-STD-1553, is undertaken. Other network standards including some emerging standards are also described.

Chapter 11 recognises that a lot of avionics functionality is achieved through software running on an avionics computer. In addition, most avionics functionality is time-critical. Software systems where time really matters are called real-time software systems. Chapter 11 explores some of the issues associated with running a number of time-critical applications on a single (or resource-limited) avionics computer. Scheduling of tasks is explored through a worked example of rate-monotonic scheduling. Chapter 12 is the final chapter of the book and covers the critical interface between the pilot and the aircraft; the cockpit. Human physiology (centred around human vision and hearing) is explored to the extent necessary to describe interface technology being employed in today’s cockpit. Well known systems like head-up displays are discussed in this chapter. Chapter 12 also investigates image intensification in the form of night-vision goggles that are starting to play a major role in both military and civilian cockpits.

The book has three appendices to help the reader with the material in the text. Appendix A is a list of the (many) acronyms used throughout the text. Although initially difficult to grasp, acronyms are a fact of life in aviation and avionics, and practitioners must become familiar with them. Appendix B contains an explanation of the equipment designation system used for a majority of military electronic equipment and for some civilian equipment. Like acronyms, practitioners should become familiar with this designation system to allow them to follow technical conversations with ease. For example, an aircraft might use a system called the AN/APS-137. Without any knowledge of what this system is, an avionics specialist knows this is some sort of airborne search radar simply by its designation. Knowing this designation system is very useful. The final appendix, Appendix C, contains the Greek alphabet and the engineering prefixes that dominate engineering topics. Again, professionals in this field need to be intimately familiar with both the Greek alphabet and the standard engineering prefixes.

Table of contents

CONTENTS
1	INTRODUCTION	1
1.1	Aircraft Functionality	1
1.2	Aircraft Systems	3
1.3	Avionics History and Direction	8
1.4	Avionics Drivers	10
1.5	Major Avionics Components	12
1.6	Summary	15
1.7	Revision Questions	16
2	AIRCRAFT ELECTRICAL SYSTEMS	17
2.1	Generating AC Power	18
2.2	Generating DC Power	26
2.3	Aircraft Batteries	28
2.4	Summary of Electrical Components	29
2.5	Standard Aircraft Electrical Outputs	29
2.6	Electrical Design Principles	34
2.7	Current and Future Directions	39
2.8	Summary	40
2.9	Revision Questions	40
3	FLIGHT-CONTROL SYSTEMS	43
3.1	Aerodynamic Stability	43
3.2	Aircraft Dynamics	45
3.3	Reference Frames	46
3.4	Traditional Flight-Control Systems	47
3.5	Fly-by-wire Flight Control	49
3.6	Auto-Pilot Examples	51
3.7	Flight-control Systems Design Issues	53
3.8	Summary	56
3.9	Revision Questions	57
4	AIR-DATA SENSORS	59
4.1	Introduction	59
4.2	Principal Components of an Air-Data System	62
4.3	Typical Applications of Air Data	63
4.4	Air-data Calculations	65
4.5	Summary	73
4.6	Revision Questions	73
5	INERTIAL SENSORS	75
5.1	Introduction	75
5.2	Gyroscopes	75
5.3	Accelerometers	87
5.4	Inertial Sensor Error and Alignment	88
5.5	Summary	88
5.6	Revision Questions	89
6	RADAR SENSORS	91
6.1	Introduction	91
6.2	Radar Introduction and Basic Pulse Radar	91
6.3	Radar Antennas	94
6.4	Radar Range Equation	103
6.5	Radar Altimeters	107
6.6	Pulse Doppler Radar Concepts	111
6.7	Doppler/Heading Reference Systems	114
6.8	Case Study	115
6.9	Summary	117
6.1	Revision Questions	117
7	ELECTRO-OPTICAL SENSORS	119
7.1	Introduction	119
7.2	Examples of an Operational EO System	120
7.3	Electro-optical Detection Scenario	122
7.4	Atmospheric Transmission	123
7.5	Relevant Laws of Physics	125
7.6	Basic EO System	130
7.7	Image Scanning and Tracking	134
7.8	Case Study: AIM-9 Air-to-air Missile	136
7.9	Worked Example	140
7.1	Summary	143
7.11	Revision Questions	143
8	COMMUNICATION SYSTEMS	145
8.1	Introduction	145
8.2	Propagation Fundamentals	145
8.3	Basic Communication Theory	154
8.4	Communication System Components	155
8.5	Data Communications	164
8.6	Identification	169
8.7	Summary	172
8.8	Revision Questions	173
9	NAVIGATION SYSTEMS	175
9.1.	Introduction	175
9.2.	Geometry of The Earth	176
9.3.	Dead-Reckoning Calculations	179
9.4.	External Navigation Aids	190
9.5.	Multi-System Integration	213
9.6.	Summary	215
9.7.	Revision Questions	215
10	AVIONICS ARCHITECTURES	217
10.1	Introduction	217
10.2	Architectures: Past, Current, and Future	217
10.3	Data Bus Characteristics and Architectural Options	225
10.4	Data Bus Topologies	230
10.5	Data Bus Media	233
10.6	Examples of Popular Avionics Data Buses	234
10.7	Summary	254
10.8	Revision Questions	254
11	AVIONICS SOFTWARE	257
11.1	Operational Flight Programs	257
11.2	Real-Time Software Considerations	259
11.3	Worked Example	270
11.4	Summary	276
11.5	Revision Questions	277
12	COCKPIT SYSTEMS	279
12.1	Major Human Senses	284
12.2	Cockpit Design Guidelines	286
12.3	Cockpit Technologies	292
12.4	Summary	306
12.5	Revision Questions	307

Sample Chapter

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