Aircraft Systems
Description
Aircraft Systems offers an examination of the most recent developments in aviation as it relates to instruments, radio navigation, and communication. Written by a noted authority in the field, the text includes in-depth descriptions of traditional systems, reviews the latest developments, as well as gives information on the technologies that are likely to emerge in the future. The author presents material on essential topics including instruments, radio propagation, communication, radio navigation, inertial navigation, and puts special emphasis on systems based on MEMS.
This vital resource also provides chapters on solid state gyroscopes, magnetic compass, propagation modes of radio waves, and format of GPS signals. Aircraft Systems is an accessible text that includes an investigation of primary and secondary radar, the structure of global navigation satellite systems, and more. This important text:
* Contains a description of the historical development of the latest technological developments in aircraft instruments, communications and navigation
* Gives several "interesting diversion" topics throughout the chapters that link the topics discussed to other developments in aerospace
* Provides examples of instruments and navigation systems in actual use in cockpit photographs obtained during the authors work as a flight instructor
* Includes numerous worked examples of relevant calculations throughout the text and a set of problems at the end of each chapter
Written for upper undergraduates in aerospace engineering and pilots in training, Aircraft Systems offers an essential guide to both the traditional and most current developments in aviation as it relates to instruments, radio navigation, and communication.
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PROF. CHRIS BINNS is an Emeritus professor at the Department of Physics and Astronomy with the University of Leicester,??UK. Currently he is a??flight instructor and continues to teach engineers at universities in Greece and in the UK.
Content
Acknowledgments xiii
About the Companion Website xv
1 Historical Development 1
1.1 Introduction 1
1.2 The Advent of Instrument Flight 2
1.3 Development of Flight Instruments Based on Air Pressure 5
1.3.1 The Altimeter 5
1.3.2 The Vertical Speed Indicator (Variometer) 7
1.3.3 The Airspeed Indicator 8
1.4 Development of Flight Instruments Based on Gyroscopes 10
1.5 Development of Aircraft Voice Communications 12
1.6 Development of Aircraft Digital Communications 19
1.6.1 Communication Via Satellite (SATCOM) 19
1.6.2 Secondary Surveillance Radar (SSR) and Traffic Alert and Collision Avoidance System (TCAS) 20
1.6.3 Aircraft Communications Addressing and Reporting System (ACARS) 23
1.7 Development of Radio Navigation 24
1.7.1 Radio Direction Finding 24
1.7.2 Guided Radio Beam Navigation 28
1.7.3 VHF/UHF Radio Navigation Systems 31
1.8 Area and Global Navigation Systems 40
1.8.1 Hyperbolic Navigation 40
1.8.2 Global Navigation Satellite Systems (GNSS) 44
1.8.3 Inertial Navigation Systems (INS) 48
1.8.4 Combining Systems: Performance-Based Navigation (PBN) and Required Navigation Performance (RNP) 53
1.9 Development of Auto Flight Control Systems 57
References 65
2 Pressure Instruments 67
2.1 Layers of the Atmosphere 67
2.2 The International Standard Atmosphere (ISA) 68
2.3 Nonstandard Atmospheres 72
2.4 Dynamic Pressure and the Bernoulli Equation 73
2.5 Definition of Sea Level and Elevation 77
2.6 Definition of Height, Altitude, and Flight Level 77
2.7 Pitot and Static Sources 80
2.8 Pressure Altimeter 81
2.8.1 Basic Principles of the Pressure Altimeter 81
2.8.2 Altimeter Display 86
2.8.3 Servo Altimeter 89
2.8.4 Altimeter with Digital Encoder 91
2.9 Vertical Speed Indicator (VSI) 93
2.9.1 Instantaneous Vertical Speed Indicator (IVSI) 98
2.10 Airspeed Indicator 100
2.11 Mach Meter 105
2.11.1 Critical Mach Number 105
2.11.2 Direct-Reading Mach Meter 107
2.12 OAT Probe 109
2.12.1 Ram Rise and Total Air Temperature 109
2.12.2 Direct-Reading Thermometer for Low Airspeeds 110
2.12.3 Resistance Thermometer Probes 110
2.13 Pitot-Static Systems 113
2.14 Air Data Computer (ADC) 117
2.14.1 Altitude and Vertical Speed 117
2.14.2 TAS and Mach number in Compressible Flow 117
2.14.3 ADC Inputs and Outputs 119
Problems 121
References 121
3 Gyroscopic and Magnetic Instruments 123
3.1 Mechanical Gyroscopes and Instruments 123
3.1.1 Basic Properties of Mechanical Gyroscopes 123
3.1.2 Gyroscope Wander 124
3.1.3 Labeling of Aircraft Axes and Rotations 125
3.1.4 Types of Gyroscope 126
3.1.5 Power for Gyroscopic Instruments 126
3.1.6 Direction Indicator (DI) 127
3.1.7 Earth Rate 129
3.1.8 Transport Wander 131
3.1.9 Attitude Indicator (AI) 134
3.1.10 Turn and Slip Indicator and Turn Coordinator 138
3.2 Solid-State Gyroscopes 141
3.2.1 The Advantages of Solid-State Gyroscopes 141
3.2.2 The Sagnac Effect 141
3.2.3 Fiber-Optic Gyroscope 142
3.2.4 Ring Laser Gyroscope 143
3.2.5 Micro-Electromechanical System (MEMS) Gyroscopes 146
3.2.6 MEMS Accelerometers 148
3.3 Magnetic Compass 149
3.3.1 Terrestrial Magnetism 149
3.3.2 Direct Indicating Magnetic Compass 151
3.3.3 Flux Gate Sensor 156
3.3.4 Miniature Magnetometers 159
3.4 Attitude Heading and Reference System (AHRS) 161
3.5 Sensor Fusion 162
Problems 163
References 165
4 Radio Propagation and Communication 167
4.1 Basic Properties of Radio Waves 167
4.2 Propagation of Radio Waves 169
4.2.1 Attenuation 169
4.2.2 Non-Ionospheric Propagation 171
4.2.2.1 Surface (or Ground) Wave: 20 kHz to 50 MHz (LF-HF) 171
>50 MHz (VHF) 172
4.2.3 Ionospheric Propagation (Skywaves) 173
4.2.3.1 Origin of the Ionosphere 173
4.2.3.2 Reflection and Absorption of Radio Waves by the Ionosphere 176
4.2.3.3 Ducting Propagation of Very Low Frequency (VLF) Waves 178
4.3 Transmitters, Receivers, and Signal Modulation 178
4.3.1 Basic Continuous Wave Morse Code Transmitter/Receiver 178
4.3.2 Quadrature Amplitude Modulation of Carrier 180
4.3.3 Superheterodyne Receivers and Demodulation of QAM Signals 182
4.3.4 Amplitude Modulated (AM) Transmission 184
4.3.5 Channel Spacing in the VHF Band for AM Voice Transmission 187
4.3.6 Frequency Modulation 189
4.3.7 Modulation for Digital Data Transmission 193
4.3.7.1 Pulsed Modulation 193
4.3.7.2 Binary Phase Shift Keying (BPSK) 193
4.3.7.3 Binary Continuous Phase Frequency Shift Keying (BCPFSK) 196
4.3.8 ITU Codes for Radio Emissions 198
4.4 Antennas 198
4.4.1 Basic Antenna Theory 198
4.4.2 Resonant Half-Wave Dipole and Quarter-Wave Monopole Antennas for VHF and UHF 206
4.4.3 Effect of Ground and Airframe on Radiation Pattern 211
4.4.4 Feeders, Transmission Lines, Impedance Matching, and Standing Wave Ratio 212
4.4.5 HF Antennas for Sky wave Communications 215
4.4.6 Low-Frequency Small Loop Antenna 215
4.4.7 Directional Antennas in the VHF and UHF Bands 216
4.4.7.1 Yagi-Uda Antenna 217
4.4.7.2 Log-Periodic Antenna 219
4.4.8 Directional Antennas in the SHF Band 220
4.4.8.1 Waveguides as Feeders 220
4.4.8.2 Horn Antenna 222
4.4.8.3 Parabolic Dish Antenna 226
4.4.8.4 Slotted Array 229
4.4.8.5 Patch or Micro strip Antenna 231
4.5 VHF Communications System 233
4.6 Long-Range HF Communications System 237
4.6.1 Coverage and Frequency Bands 237
4.6.2 Selective Calling (SELCAL) 240
4.6.3 HF Ground Station Network 240
4.6.4 HF Data Link (HFDL) 242
4.7 Satellite Communications 242
4.8 Aircraft Communications Addressing and Reporting System (ACARS) 245
Problems 247
References 248
5 Primary and Secondary Radar 249
5.1 Primary Radar 249
5.2 Ground Radar 257
5.3 Airborne Weather Radar 258
5.4 Secondary Surveillance Radar (SSR) 272
5.4.1 Mode A and Mode C Interrogation Pulses 273
5.4.2 Mode A Reply from the Aircraft 274
5.4.3 Mode C Reply from the Aircraft 275
5.4.4 Conflicts Between Mode A and Mode C Replies from Different Aircraft 276
5.4.5 Mode S 276
5.4.6 Mode S All Call Interrogation 277
5.4.7 Mode S Selective Call Interrogation 278
5.4.8 Mode S Reply from Aircraft 279
5.4.9 Traffic Surveillance by Mode S 280
5.4.10 Squitters and Automatic Dependent Surveillance Broadcast (ADS-B) 281
5.4.11 Universal Access Transceivers (UAT) and ADS-B 283
5.4.12 Surveillance by ADS-B 286
5.5 Traffic Collision Avoidance System (TCAS) 288
5.6 Radio Altimeter 291
Problems 293
References 294
6 General Principles of Navigation 295
6.1 Coordinate Reference System for the Earth 295
6.1.1 Latitude and Longitude 295
6.1.2 Great Circle Routes, Rhumb Lines, and Departure 297
6.2 Compass Heading, Variation, and Deviation 302
6.3 Aviation Charts 305
6.3.1 General Chart Properties: Chart Scale, Orthomorphism, and Conformality 305
6.3.2 Chart Projections 308
6.3.2.1 Mercator Projection 308
6.3.2.2 Conical Projection 311
6.3.2.3 Gnomic and Polar Stereographic Projection 313
6.4 Non-Sphericity of the Earth and the WGS84 Model 315
6.5 Navigation by Dead Reckoning 319
6.5.1 Calculating the True Airspeed 320
6.5.2 Calculating the Heading and Ground Speed in a Known Wind 321
6.5.3 Pilot Log for a Visual Flight Rules (VFR) Navigation 324
6.5.4 Correcting Track Errors 327
Problems 331
References 332
7 Short-Range Radio Navigation 333
7.1 Automatic Direction Finder (ADF) 334
7.1.1 Principle of Operation 334
7.1.2 ADF Cockpit Instrumentation 336
7.2 VHF Omnidirectional Range (VOR) 342
7.2.1 Principle of Operation 342
7.2.2 Conventional VOR (CVOR) 344
7.2.3 Doppler VOR (DVOR) 348
7.2.4 VOR Cockpit Instrumentation 351
7.2.5 VOR Track Errors 354
7.2.6 Airways System Defined by VORs 358
7.2.7 Area Navigation (RNAV) 360
7.3 Distance Measuring Equipment (DME) 365
7.4 Instrument Landing System (ILS) 366
7.4.1 ILS Localizer 367
7.4.2 ILS Glide Slope 375
7.4.3 ILS Cockpit Instrumentation 378
7.4.4 Categories of ILS 379
7.5 Microwave Landing System (MLS) 381
Problems 383
References 385
8 Global Navigation Satellite System (GNSS) 387
8.1 Basic Principle of Satellite Navigation 387
8.2 The Constellation of Space Vehicles (SVs) 389
8.2.1 Orbital Radius of the GPS Constellation 389
8.2.2 Orbital Arrangement for Optimal Coverage by the GPS Constellation 391
8.3 Transmissions by the GPS SVs 395
8.3.1 GPS Time and UTC 395
8.3.2 Transmission Channels 396
8.3.3 Construction of the C/A Code 398
8.3.4 Multiplexed Decoding of the Navigation Message 400
8.3.5 Format of the Navigation Message 405
8.3.6 Precision P(Y) Code 413
8.3.7 Additional GPS Signals 413
8.3.7.1 L2C Signal 414
8.3.7.2 L5 Safety of Life Signal 415
8.3.7.3 L1C Signal 416
8.3.7.4 L3 and L4 Signals 416
8.4 Control Segment 419
8.5 Sources of GPS Errors 421
8.5.1 Geometric Dilution of Position 421
8.5.2 Ionospheric Propagation Error 421
8.5.3 Other Sources of Error 423
8.6 Relativity Corrections Required for GPS 424
8.7 Augmentation Systems 425
8.7.1 Wide Area Augmentation Systems (WAAS) 425
8.7.2 Local Area Augmentation Systems (LAAS) 426
8.7.3 Aircraft-Based Augmentation Systems (ABAS) and Receiver Autonomous Integrity Monitoring (RAIM) 426
8.8 GPS Cockpit Instrumentation 428
8.9 Spoofing, Meaconing, and Positioning, Navigation, and Timing (PNT) Resilience 430
Problems 430
References 431
9 Inertial Navigation and Kalman Filtering 433
9.1 Basic Principle of Inertial Navigation 433
9.2 Gimbaled Systems 435
9.2.1 Stabilized Platforms 435
9.2.2 Obtaining Latitude and Longitude 436
9.2.3 Correcting the Platform Orientation for Earth Rate and Transport Wander 437
9.2.4 Initializing the Platform 439
9.3 Strapdown Systems 440
9.4 Accelerations Not due to Changes in Aircraft Motion 442
9.5 Schüler Oscillations 443
9.6 Earth-Loop Oscillations 445
9.7 Summary of Inertial Guidance Errors 445
9.7.1 Sensor Bias 446
9.7.2 Random Walk Position Error Produced by Sensor Noise 447
9.7.3 Environmental Factors 447
9.7.4 True Wander 448
9.8 Cockpit Instrumentation 449
9.9 Kalman Filter 451
9.9.1 Basic Principle of the Kalman Filter 451
9.9.2 Kalman Filter for One-Dimensional (Single Value) Data 454
9.9.3 Kalman Filtering of Multiple values 455
Problems 460
References 461
Appendix A Radiation from Wire Antennas 463
Appendix B Theory of Transmission Lines and Waveguides 475
Appendix C Effective Aperture of a Receiving Antenna 481
Appendix D Acronyms 485
Index 489
1
Historical Development
1.1 Introduction
If you board a commercial flight in 2016, you will step onto an aircraft that has a significant redundancy of electrical power and safety systems with a high level of automation. The instruments in the cockpit show the pilots via highly ergonomic displays the attitude, height, climb rate, speed, and Mach number of the aircraft as well as the state of the engines and other factors such as the outside air temperature and the wind speed and direction. On-board weather radar informs the pilots of storms in the path with detailed information about the precipitation, turbulence, and the lateral and vertical extent of the storms. The navigation system takes inputs from GPS satellites, an inertial reference system (IRS), and VHF radio beacons; filters the information; and provides a precise indication of the position of the aircraft in three dimensions to within a few meters. These same instruments and navigation systems provide information to the autopilot, which can control the aircraft in height and position to follow a specific flight plan and land the plane at the destination airport if the latter has the necessary ground systems installed. The navigation computer contains a detailed database of all man-made and natural potential obstacles and provides warnings of approaching terrain or structures. The flight is conducted via a comprehensive air traffic control (ATC) system that tracks the aircraft and maintains communication links with the pilots throughout the flight to ensure safe separation with other aircraft. In addition, the aircraft will communicate automatically with others in the local area and build a three-dimensional map of all nearby flights to provide a traffic avoidance system that is independent of ground air traffic controllers. The system will not only warn the pilots of nearby traffic but also in extreme cases will inform them what evasive action to take. These and other systems have led to an unprecedented level of safety in commercial air travel which, if represented as fatalities per km traveled, is safer than any other type of transport on water or land [1]. This parameter does not necessarily provide the fairest comparison between different modes of travel since air travel will naturally do well with any safety assessment that uses distance traveled as the criterion. For example, when using fatalities per hour traveled, aviation drops to third on the list below rail and bus transport. It remains true, however, that air travel safety has made vast improvements by any measure in the last few decades and this is largely due to the incorporation of the systems listed above. All of these will be described in detail in subsequent chapters but before delving into the technical complexity it is worth exploring, in this chapter, a condensed history of the development of some of those instruments and systems.
1.2 The Advent of Instrument Flight
In the earliest days of aviation, the pilot's senses were the main aircraft instruments, with vision being used to estimate speed, height, and flight attitude while hearing and smell were used to monitor the state of health of the engine. The Wright flyer did have instruments installed including an anemometer, a stopwatch, and a revolution counter but these were used exclusively to analyze the performance of the flyer and the engine post landing. The flight itself was conducted entirely utilizing the senses of the pilot. Flying by senses alone dominated aviation throughout the First World War and led to the myth of instinctive balance when flying an aeroplane. This remained while flights were rarely conducted in bad weather and small rolled attitudes that developed inadvertently while flying through an individual cloud went unheeded. After the war, airmail and the first passenger services started to be developed but initially these flew under the weather sometimes at very low altitude resulting in many fatalities.
It was realized by the end of the First World War that flying in cloud with pilot vision completely removed from the available information could quickly lead to spatial disorientation and the aircraft spiraling out of the cloud with complete loss of control. The problem is that inner ear senses, which measure linear and angular acceleration, are evolved for life on the ground and provide misleading sensations in aircraft. Examples include the Somatogyral illusion in which an established banked turn is undetected as there is no angular acceleration but rolling out of the turn produces the illusion of a bank in the opposite direction, and the Somatogravic illusion where accelerations and decelerations are interpreted as pitches up and down, respectively. Gyroscopic turn coordinators were available by 1918 but without instrument training pilots still tended to favor their senses over the indications of the instrument.
Early pioneers in the development of instrument flight were two US army pilots, William Ocker and Carl Crane. By 1918, the first gyroscope-based attitude indicators (AIs) (see Section 1.4 and Section 3.1.9), invented by Elmer Sperry, were available and Ocker was one of the first to attempt an extended flight in cloud using the instrument. The flight still ended up with the aircraft in a spiral dive but Ocker realized that the main reason was his failure to put complete faith in the instrument and to pay too much attention to his erroneous balance senses. Ocker was one of the first to correctly identify the misinformation coming from balance organs and became somewhat of an evangelist for using instruments in flight. Crane was nearly killed in 1925 when he dropped into a spiral dive out of cloud while flying a congressman's son to Washington and was acutely aware of the problems of maintaining control while blind. Ocker and Crane teamed up in 1929 and conducted a comprehensive study of flying in clouds, which led, in 1932, to the publication of their book, Blind Flight in Theory and Practice, which is the first systematic exploration of instrument flight. By the late 1920s, a full range of pressure and gyro instruments were available as well as some radio navigation devices (see below) and in 1929 Jimmy Doolittle demonstrated a "blind" takeoff, aerodrome circuit, and landing in an aircraft whose dome was covered [2]. The cockpit in Doolittle's NY-2 Husky biplane is shown in Figure 1.1a and contains the six main glass instruments that are to be found in a current general aviation (GA) light aircraft. That is, an altimeter (i), an AI (ii), an airspeed indicator (iii), a turn indicator or turn coordinator (iv), a direction indicator (DI) (v), and a vertical speed indicator (VSI) (vi). By the 1950s, the layout of these six instruments was standardized into what was deemed to be the most ergonomic arrangement (the so-called "6-pack") and they were mounted as shown in Figure 1.1b, which shows a Piper PA28 cockpit.
Figure 1.1 (a) Flight instruments in the cockpit of the NY-2 Husky biplane used in the first "blind" takeoff and landing flight by Doolittle in 1929.
Source: Reproduced from Ref. [2] with permission of ETHW.
(b) The same six instruments in the standard layout in a 1960's light aircraft (Piper PA28).
In older large aircraft with traditional instruments, the standard 6-pack is also evident directly in front of the pilot though it is embedded in an extended array of engine and navigation instruments. The main change to this layout came in the transition to "glass cockpits" in the late 1960s where several instruments are displayed on a single electronic screen. The term is slightly misleading as there is probably less glass in a glass cockpit than a traditional one with a large array of glass-fronted instruments but basically it means information is displayed on electronic screens rather than individual instruments. The change to glass cockpits marked the transition from direct-sensing to remote-sensing instrumentation. In the case of older direct-sensing pressure instruments, the pressure being measured is brought via tubes directly into the back of the instrument, which then converts it into a reading on the instrument face as described in Chapter 2. This leads to a large amount of tubing mixed in with all the wiring behind the instrument panel. In remote sensing, a transducer measures the quantity required remotely and converts it into an analog or digital electrical signal, which is conveyed by wires, either to an individual instrument, or to a computer and display generator. In the most modern systems, a digital data bus is used to convey information from all the sensors, which significantly reduces the complexity of the wiring. Figure 1.2 compares a cockpit with traditional direct-sensing instruments in a twin piston engine aircraft (Figure 1.2a) and a glass cockpit in which the remote-sensing instruments communicate via a computer to the electronic displays, again in a twin piston engine aircraft (Figure 1.2b). Note, however, that even in the glass cockpit there are some direct-sensing instruments provided as backup in case of a total power failure. The glass screen immediately in front of the left pilot seat is referred to as the Primary Flight Display (PFD).
Figure 1.2 (a) Instrument display in the cockpit of a twin piston engine aircraft using entirely analog...
