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Small Unmanned Fixed-wing Aircraft Design: A Practical Approach

ISBN: 978-1-119-40631-0
496 pages
August 2017
Small Unmanned Fixed-wing Aircraft Design: A Practical Approach (1119406315) cover image

Description

Small Unmanned Fixed-wing Aircraft Design is the essential guide to designing, building and testing fixed wing UAVs (or drones). It deals with aircraft from two to 150 kg in weight and is based on the first-hand experiences of the world renowned UAV team at the UK’s University of Southampton. 

The book covers both the practical aspects of designing, manufacturing and flight testing and outlines and the essential calculations needed to underpin successful designs. It describes the entire process of UAV design from requirements definition to configuration layout and sizing, through preliminary design and analysis using simple panel codes and spreadsheets to full CFD and FEA models and on to detailed design with parametric CAD tools. Its focus is on modest cost approaches that draw heavily on the latest digital design and manufacturing methods, including a strong emphasis on utilizing off-the-shelf components, low cost analysis, automated geometry modelling and 3D printing. 

It deliberately avoids a deep theoretical coverage of aerodynamics or structural mechanics; rather it provides a design team with sufficient insights and guidance to get the essentials undertaken more pragmatically. The book contains many all-colour illustrations of the dozens of aircraft built by the authors and their students over the last ten years giving much detailed information on what works best. It is predominantly aimed at under-graduate and MSc level student design and build projects, but will be of interest to anyone engaged in the practical problems of getting quite complex unmanned aircraft flying. It should also appeal to the more sophisticated aero-modeller and those engaged on research based around fixed wing UAVs. 

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Table of Contents

List of Figures xvii

List of Tables xxxiii

Foreword xxxv

Series Preface xxxvii

Preface xxxix

Acknowledgments xli

PART I INTRODUCING FIXED-WING UAVS

1 Preliminaries 3

1.1 Externally Sourced Components 4

1.2 Manufacturing Methods 5

1.3 Project DECODE 6

1.4 The Stages of Design 6

1.4.1 Concept Design 8

1.4.2 Preliminary Design 10

1.4.3 Detail Design 11

1.4.4 Manufacturing Design 12

1.4.5 In-service Design and Decommissioning 13

1.5 Summary 13

2 Unmanned Air Vehicles 15

2.1 A Brief Taxonomy of UAVs 15

2.2 The Morphology of a UAV 19

2.2.1 Lifting Surfaces 21

2.2.2 Control Surfaces 22

2.2.3 Fuselage and Internal Structure 23

2.2.4 Propulsion Systems 24

2.2.5 Fuel Tanks 24

2.2.6 Control Systems 24

2.2.7 Payloads 27

2.2.8 Take-off and Landing Gear 27

2.3 Main Design Drivers 29

PART II THE AIRCRAFT IN MORE DETAIL

3 Wings 33

3.1 Simple Wing Theory and Aerodynamic Shape 33

3.2 Spars 37

3.3 Covers 37

3.4 Ribs 38

3.5 Fuselage Attachments 38

3.6 Ailerons/Roll Control 40

3.7 Flaps 41

3.8 Wing Tips 42

3.9 Wing-housed Retractable Undercarriage 42

3.10 Integral Fuel Tanks 44

4 Fuselages and Tails (Empennage) 45

4.1 Main Fuselage/Nacelle Structure 45

4.2 Wing Attachment 47

4.3 Engine and Motor Mountings 48

4.4 Avionics Trays 50

4.5 Payloads – Camera Mountings 51

4.6 Integral Fuel Tanks 52

4.7 Assembly Mechanisms and Access Hatches 54

4.8 Undercarriage Attachment 55

4.9 Tails (Empennage) 57

5 Propulsion 59

5.1 Liquid-Fueled IC Engines 59

5.1.1 Glow-plug IC Engines 62

5.1.2 Spark Ignition Gasoline IC Engines 62

5.1.3 IC Engine Testing 65

5.2 Rare-earth Brushless Electric Motors 66

5.3 Propellers 68

5.4 Engine/Motor Control 70

5.5 Fuel Systems 70

5.6 Batteries and Generators 71

6 Airframe Avionics and Systems 73

6.1 Primary Control Transmitter and Receivers 73

6.2 Avionics Power Supplies 76

6.3 Servos 78

6.4 Wiring, Buses, and Boards 82

6.5 Autopilots 86

6.6 Payload Communications Systems 87

6.7 Ancillaries 88

6.8 Resilience and Redundancy 90

7 Undercarriages 93

7.1 Wheels 93

7.2 Suspension 95

7.3 Steering 95

7.4 Retractable Systems 97

PART III DESIGNING UAVS

8 The Process of Design 101

8.1 Goals and Constraints 101

8.2 Airworthiness 103

8.3 Likely Failure Modes 104

8.3.1 Aerodynamic and Stability Failure 105

8.3.2 Structural Failure 106

8.3.3 Engine/Motor Failure 107

8.3.4 Control System Failure 107

8.4 Systems Engineering 110

8.4.1 Work-breakdown Structure 110

8.4.2 Interface Definitions 112

8.4.3 Allocation of Responsibility 112

8.4.4 Requirements Flowdown 112

8.4.5 Compliance Testing 113

8.4.6 Cost and Weight Management 114

8.4.7 Design “Checklist” 117

9 Tool Selection 119

9.1 Geometry/CAD Codes 120

9.2 Concept Design 123

9.3 Operational Simulation and Mission Planning 125

9.4 Aerodynamic and Structural Analysis Codes 125

9.5 Design and Decision Viewing 125

9.6 Supporting Databases 126

10 Concept Design: Initial Constraint Analysis 127

10.1 The Design Brief 127

10.1.1 Drawing up a Good Design Brief 127

10.1.2 Environment and Mission 128

10.1.3 Constraints 129

10.2 Airframe Topology 130

10.2.1 Unmanned versus Manned – Rethinking Topology 130

10.2.2 Searching the Space of Topologies 133

10.2.3 Systematic “invention” of UAV Concepts 136

10.2.4 Managing the Concept Design Process 144

10.3 Airframe and Powerplant Scaling via Constraint Analysis 144

10.3.1 The Role of Constraint Analysis 144

10.3.2 The Impact of Customer Requirements 145

10.3.3 Concept Constraint Analysis – A Proposed Computational Implementation 145

10.3.4 The Constraint Space 146

10.4 A Parametric Constraint Analysis Report 146

10.4.1 About This Document 146

10.4.2 Design Brief 147

10.4.3 Unit Conversions 149

10.4.4 Basic Geometry and Initial Guesses 151

10.4.5 Preamble 151

10.4.6 Preliminary Calculations 152

10.4.7 Constraints 154

10.5 The Combined Constraint Diagram and Its Place in the Design Process 162

11 Spreadsheet-Based Concept Design and Examples 165

11.1 Concept Design Algorithm 166

11.2 Range 169

11.3 Structural Loading Calculations 169

11.4 Weight and CoG Estimation 170

11.5 Longitudinal Stability 170

11.6 Powering and Propeller Sizing 171

11.7 Resulting Design: Decode-1 174

11.8 A Bigger Single Engine Design: Decode-2 177

11.9 A Twin Tractor Design: SPOTTER 182

12 Preliminary Geometry Design 189

12.1 Preliminary Airframe Geometry and CAD 190

12.2 Designing Decode-1 with AirCONICS 192

13 Preliminary Aerodynamic and Stability Analysis 195

13.1 Panel Method Solvers – XFoil and XFLR5 196

13.2 RANS Solvers – Fluent 200

13.2.1 Meshing, Turbulence Model Choice, and y+ 204

13.3 Example Two-dimensional Airfoil Analysis 208

13.4 Example Three-dimensional Airfoil Analysis 210

13.5 3D Models of Simple Wings 212

13.6 Example Airframe Aerodynamics 214

13.6.1 Analyzing Decode-1 with XFLR5: Aerodynamics 215

13.6.2 Analyzing Decode-1 with XFLR5: Control Surfaces 221

13.6.3 Analyzing Decode-1 with XFLR5: Stability 223

13.6.4 Flight Simulators 227

13.6.5 Analyzing Decode-1 with Fluent 228

14 Preliminary Structural Analysis 237

14.1 Structural Modeling Using AirCONICS 240

14.2 Structural Analysis Using Simple Beam Theory 243

14.3 Finite Element Analysis (FEA) 245

14.3.1 FEA Model Preparation 246

14.3.2 FEA Complete Spar and Boom Model 250

14.3.3 FEA Analysis of 3D Printed and Fiber- or Mylar-clad Foam Parts 255

14.4 Structural Dynamics and Aeroelasticity 265

14.4.1 Estimating Wing Divergence, Control Reversal, and Flutter Onset

Speeds 266

14.5 Summary of Preliminary Structural Analysis 272

15 Weight and Center of Gravity Control 273

15.1 Weight Control 273

15.2 Longitudinal Center of Gravity Control 279

16 Experimental Testing and Validation 281

16.1 Wind Tunnels Tests 282

16.1.1 Mounting the Model 282

16.1.2 Calibrating the Test 284

16.1.3 Blockage Effects 284

16.1.4 Typical Results 287

16.2 Airframe Load Tests 290

16.2.1 Structural Test Instruments 290

16.2.2 Structural Mounting and Loading 293

16.2.3 Static Structural Testing 294

16.2.4 Dynamic Structural Testing 296

16.3 Avionics Testing 300

17 Detail Design: Constructing Explicit Design Geometry 303

17.1 The Generation of Geometry 303

17.2 Fuselage 306

17.3 An Example UAV Assembly 309

17.3.1 Hand Sketches 311

17.3.2 Master Sketches 311

17.4 3D Printed Parts 313

17.4.1 Decode-1: The Development of a Parametric Geometry for the SLS Nylon Wing Spar/Boom “Scaffold Clamp” 313

17.4.2 Approach 314

17.4.3 Inputs 314

17.4.4 Breakdown of Part 315

17.4.5 Parametric Capability 316

17.4.6 More Detailed Model 317

17.4.7 Manufacture 318

17.5 Wings 318

17.5.1 Wing Section Profile 320

17.5.2 Three-dimensional Wing 323

PART IV MANUFACTURE AND FLIGHT

18 Manufacture 331

18.1 Externally Sourced Components 331

18.2 Three-Dimensional Printing 332

18.2.1 Selective Laser Sintering (SLS) 332

18.2.2 Fused Deposition Modeling (FDM) 335

18.2.3 Sealing Components 335

18.3 Hot-wire Foam Cutting 337

18.3.1 Fiber and Mylar Foam Cladding 339

18.4 Laser Cutting 339

18.5 Wiring Looms 342

18.6 Assembly Mechanisms 342

18.6.1 Bayonets and Locking Pins 345

18.6.2 Clamps 346

18.6.3 Conventional Bolts and Screws 346

18.7 Storage and Transport Cases 347

19 Regulatory Approval and Documentation 349

19.1 Aviation Authority Requirements 349

19.2 System Description 351

19.2.1 Airframe 352

19.2.2 Performance 355

19.2.3 Avionics and Ground Control System 356

19.2.4 Acceptance Flight Data 358

19.3 Operations Manual 358

19.3.1 Organization, Team Roles, and Communications 359

19.3.2 Brief Technical Description 359

19.3.3 Operating Limits, Conditions, and Control 359

19.3.4 Operational Area and Flight Plans 360

19.3.5 Operational and Emergency Procedures 360

19.3.6 Maintenance Schedule 360

19.4 Safety Case 361

19.4.1 Risk Assessment Process 362

19.4.2 Failure Modes and Effects 362

19.4.3 Operational Hazards 363

19.4.4 Accident List 364

19.4.5 Mitigation List 364

19.4.6 Accident Sequences and Mitigation 366

19.5 Flight Planning Manual 368

20 Test Flights and Maintenance 369

20.1 Test Flight Planning 369

20.1.1 Exploration of Flight Envelope 369

20.1.2 Ranking of Flight Tests by Risk 370

20.1.3 Instrumentation and Recording of Flight Test Data 370

20.1.4 Pre-flight Inspection and Checklists 371

20.1.5 Atmospheric Conditions 371

20.1.6 Incident and Crash Contingency Planning, Post Crash Safety, Recording, and Management of Crash Site 371

20.2 Test Flight Examples 375

20.2.1 UAS Performance Flight Test (MANUAL Mode) 375

20.2.2 UAS CoG Flight Test (MANUAL Mode) 377

20.2.3 Fuel Consumption Tests 377

20.2.4 Engine Failure, Idle, and Throttle Change Tests 377

20.2.5 Autonomous Flight Control 378

20.2.6 Auto-Takeoff Test 380

20.2.7 Auto-Landing Test 380

20.2.8 Operational and Safety Flight Scenarios 381

20.3 Maintenance 381

20.3.1 Overall Airframe Maintenance 382

20.3.2 Time and Flight Expired Items 382

20.3.3 Batteries 383

20.3.4 Flight Control Software 383

20.3.5 Maintenance Record Keeping 384

21 Lessons Learned 385

21.1 Things that Have Gone Wrong and Why 388

PART V APPENDICES, BIBLIOGRAPHY, AND INDEX

A Generic Aircraft Design Flowchart 395

B Example AirCONICS Code for Decode-1 399

C Worked (Manned Aircraft) Detail Design Example 425

C.1 Stage 1: Concept Sketches 425

C.2 Stage 2: Part Definition 429

C.3 Stage 3: “Flying Surfaces” 434

C.4 Stage 4: Other Items 435

C.5 Stage 5: Detail Definition 435

Bibliography 439

Index 441

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Author Information

Andrew J. Keane is a Professor of Computational Engineering in the Faculty of Engineering and the Environment at the University of Southampton. He is the Director of the Rolls-Royce University Technology Center for Computational Engineering at the University and is a fellow of the RINA, IMechE and the Royal Academy of Engineering.

András Sóbester is a Senior Lecturer of Aeronautical Engineering in the Faculty of Engineering and the Environment at the University of Southampton. His main research focus is on developing techniques for the aerodynamic optimization of aircraft.

James P. Scanlan is a Professor of Design in the Faculty of Engineering and the Environment at the University of Southampton. He spent more than 10 years working in the aerospace industry and now manages a number of research programmes sponsored by BAE systems, Airbus, Rolls-Royce and the EPSRC. He is a Fellow of the Royal Aeronautical Society.

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