Small Unmanned Fixed-wing Aircraft Design

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.

• List of Figures xviiList of Tables xxxiiiForeword xxxvSeries Preface xxxviiPreface xxxixAcknowledgments xliPART I INTRODUCING FIXED-WING UAVS1 Preliminaries 31.1 Externally Sourced Components 41.2 Manufacturing Methods 51.3 Project DECODE 61.4 The Stages of Design 61.4.1 Concept Design 81.4.2 Preliminary Design 101.4.3 Detail Design 111.4.4 Manufacturing Design 121.4.5 In-service Design and Decommissioning 131.5 Summary 132 Unmanned Air Vehicles 152.1 A Brief Taxonomy of UAVs 152.2 The Morphology of a UAV 192.2.1 Lifting Surfaces 212.2.2 Control Surfaces 222.2.3 Fuselage and Internal Structure 232.2.4 Propulsion Systems 242.2.5 Fuel Tanks 242.2.6 Control Systems 242.2.7 Payloads 272.2.8 Take-off and Landing Gear 272.3 Main Design Drivers 29PART II THE AIRCRAFT IN MORE DETAIL3 Wings 333.1 Simple Wing Theory and Aerodynamic Shape 333.2 Spars 373.3 Covers 373.4 Ribs 383.5 Fuselage Attachments 383.6 Ailerons/Roll Control 403.7 Flaps 413.8 Wing Tips 423.9 Wing-housed Retractable Undercarriage 423.10 Integral Fuel Tanks 444 Fuselages and Tails (Empennage) 454.1 Main Fuselage/Nacelle Structure 454.2 Wing Attachment 474.3 Engine and Motor Mountings 484.4 Avionics Trays 504.5 Payloads – Camera Mountings 514.6 Integral Fuel Tanks 524.7 Assembly Mechanisms and Access Hatches 544.8 Undercarriage Attachment 554.9 Tails (Empennage) 575 Propulsion 595.1 Liquid-Fueled IC Engines 595.1.1 Glow-plug IC Engines 625.1.2 Spark Ignition Gasoline IC Engines 625.1.3 IC Engine Testing 655.2 Rare-earth Brushless Electric Motors 665.3 Propellers 685.4 Engine/Motor Control 705.5 Fuel Systems 705.6 Batteries and Generators 716 Airframe Avionics and Systems 736.1 Primary Control Transmitter and Receivers 736.2 Avionics Power Supplies 766.3 Servos 786.4 Wiring, Buses, and Boards 826.5 Autopilots 866.6 Payload Communications Systems 876.7 Ancillaries 886.8 Resilience and Redundancy 907 Undercarriages 937.1 Wheels 937.2 Suspension 957.3 Steering 957.4 Retractable Systems 97PART III DESIGNING UAVS8 The Process of Design 1018.1 Goals and Constraints 1018.2 Airworthiness 1038.3 Likely Failure Modes 1048.3.1 Aerodynamic and Stability Failure 1058.3.2 Structural Failure 1068.3.3 Engine/Motor Failure 1078.3.4 Control System Failure 1078.4 Systems Engineering 1108.4.1 Work-breakdown Structure 1108.4.2 Interface Definitions 1128.4.3 Allocation of Responsibility 1128.4.4 Requirements Flowdown 1128.4.5 Compliance Testing 1138.4.6 Cost and Weight Management 1148.4.7 Design “Checklist” 1179 Tool Selection 1199.1 Geometry/CAD Codes 1209.2 Concept Design 1239.3 Operational Simulation and Mission Planning 1259.4 Aerodynamic and Structural Analysis Codes 1259.5 Design and Decision Viewing 1259.6 Supporting Databases 12610 Concept Design: Initial Constraint Analysis 12710.1 The Design Brief 12710.1.1 Drawing up a Good Design Brief 12710.1.2 Environment and Mission 12810.1.3 Constraints 12910.2 Airframe Topology 13010.2.1 Unmanned versus Manned – Rethinking Topology 13010.2.2 Searching the Space of Topologies 13310.2.3 Systematic “invention” of UAV Concepts 13610.2.4 Managing the Concept Design Process 14410.3 Airframe and Powerplant Scaling via Constraint Analysis 14410.3.1 The Role of Constraint Analysis 14410.3.2 The Impact of Customer Requirements 14510.3.3 Concept Constraint Analysis – A Proposed Computational Implementation 14510.3.4 The Constraint Space 14610.4 A Parametric Constraint Analysis Report 14610.4.1 About This Document 14610.4.2 Design Brief 14710.4.3 Unit Conversions 14910.4.4 Basic Geometry and Initial Guesses 15110.4.5 Preamble 15110.4.6 Preliminary Calculations 15210.4.7 Constraints 15410.5 The Combined Constraint Diagram and Its Place in the Design Process 16211 Spreadsheet-Based Concept Design and Examples 16511.1 Concept Design Algorithm 16611.2 Range 16911.3 Structural Loading Calculations 16911.4 Weight and CoG Estimation 17011.5 Longitudinal Stability 17011.6 Powering and Propeller Sizing 17111.7 Resulting Design: Decode-1 17411.8 A Bigger Single Engine Design: Decode-2 17711.9 A Twin Tractor Design: SPOTTER 18212 Preliminary Geometry Design 18912.1 Preliminary Airframe Geometry and CAD 19012.2 Designing Decode-1 with AirCONICS 19213 Preliminary Aerodynamic and Stability Analysis 19513.1 Panel Method Solvers – XFoil and XFLR5 19613.2 RANS Solvers – Fluent 20013.2.1 Meshing, Turbulence Model Choice, and y+ 20413.3 Example Two-dimensional Airfoil Analysis 20813.4 Example Three-dimensional Airfoil Analysis 21013.5 3D Models of Simple Wings 21213.6 Example Airframe Aerodynamics 21413.6.1 Analyzing Decode-1 with XFLR5: Aerodynamics 21513.6.2 Analyzing Decode-1 with XFLR5: Control Surfaces 22113.6.3 Analyzing Decode-1 with XFLR5: Stability 22313.6.4 Flight Simulators 22713.6.5 Analyzing Decode-1 with Fluent 22814 Preliminary Structural Analysis 23714.1 Structural Modeling Using AirCONICS 24014.2 Structural Analysis Using Simple Beam Theory 24314.3 Finite Element Analysis (FEA) 24514.3.1 FEA Model Preparation 24614.3.2 FEA Complete Spar and Boom Model 25014.3.3 FEA Analysis of 3D Printed and Fiber- or Mylar-clad Foam Parts 25514.4 Structural Dynamics and Aeroelasticity 26514.4.1 Estimating Wing Divergence, Control Reversal, and Flutter OnsetSpeeds 26614.5 Summary of Preliminary Structural Analysis 27215 Weight and Center of Gravity Control 27315.1 Weight Control 27315.2 Longitudinal Center of Gravity Control 27916 Experimental Testing and Validation 28116.1 Wind Tunnels Tests 28216.1.1 Mounting the Model 28216.1.2 Calibrating the Test 28416.1.3 Blockage Effects 28416.1.4 Typical Results 28716.2 Airframe Load Tests 29016.2.1 Structural Test Instruments 29016.2.2 Structural Mounting and Loading 29316.2.3 Static Structural Testing 29416.2.4 Dynamic Structural Testing 29616.3 Avionics Testing 30017 Detail Design: Constructing Explicit Design Geometry 30317.1 The Generation of Geometry 30317.2 Fuselage 30617.3 An Example UAV Assembly 30917.3.1 Hand Sketches 31117.3.2 Master Sketches 31117.4 3D Printed Parts 31317.4.1 Decode-1: The Development of a Parametric Geometry for the SLS Nylon Wing Spar/Boom “Scaffold Clamp” 31317.4.2 Approach 31417.4.3 Inputs 31417.4.4 Breakdown of Part 31517.4.5 Parametric Capability 31617.4.6 More Detailed Model 31717.4.7 Manufacture 31817.5 Wings 31817.5.1 Wing Section Profile 32017.5.2 Three-dimensional Wing 323PART IV MANUFACTURE AND FLIGHT18 Manufacture 33118.1 Externally Sourced Components 33118.2 Three-Dimensional Printing 33218.2.1 Selective Laser Sintering (SLS) 33218.2.2 Fused Deposition Modeling (FDM) 33518.2.3 Sealing Components 33518.3 Hot-wire Foam Cutting 33718.3.1 Fiber and Mylar Foam Cladding 33918.4 Laser Cutting 33918.5 Wiring Looms 34218.6 Assembly Mechanisms 34218.6.1 Bayonets and Locking Pins 34518.6.2 Clamps 34618.6.3 Conventional Bolts and Screws 34618.7 Storage and Transport Cases 34719 Regulatory Approval and Documentation 34919.1 Aviation Authority Requirements 34919.2 System Description 35119.2.1 Airframe 35219.2.2 Performance 35519.2.3 Avionics and Ground Control System 35619.2.4 Acceptance Flight Data 35819.3 Operations Manual 35819.3.1 Organization, Team Roles, and Communications 35919.3.2 Brief Technical Description 35919.3.3 Operating Limits, Conditions, and Control 35919.3.4 Operational Area and Flight Plans 36019.3.5 Operational and Emergency Procedures 36019.3.6 Maintenance Schedule 36019.4 Safety Case 36119.4.1 Risk Assessment Process 36219.4.2 Failure Modes and Effects 36219.4.3 Operational Hazards 36319.4.4 Accident List 36419.4.5 Mitigation List 36419.4.6 Accident Sequences and Mitigation 36619.5 Flight Planning Manual 36820 Test Flights and Maintenance 36920.1 Test Flight Planning 36920.1.1 Exploration of Flight Envelope 36920.1.2 Ranking of Flight Tests by Risk 37020.1.3 Instrumentation and Recording of Flight Test Data 37020.1.4 Pre-flight Inspection and Checklists 37120.1.5 Atmospheric Conditions 37120.1.6 Incident and Crash Contingency Planning, Post Crash Safety, Recording, and Management of Crash Site 37120.2 Test Flight Examples 37520.2.1 UAS Performance Flight Test (MANUAL Mode) 37520.2.2 UAS CoG Flight Test (MANUAL Mode) 37720.2.3 Fuel Consumption Tests 37720.2.4 Engine Failure, Idle, and Throttle Change Tests 37720.2.5 Autonomous Flight Control 37820.2.6 Auto-Takeoff Test 38020.2.7 Auto-Landing Test 38020.2.8 Operational and Safety Flight Scenarios 38120.3 Maintenance 38120.3.1 Overall Airframe Maintenance 38220.3.2 Time and Flight Expired Items 38220.3.3 Batteries 38320.3.4 Flight Control Software 38320.3.5 Maintenance Record Keeping 38421 Lessons Learned 38521.1 Things that Have Gone Wrong and Why 388PART V APPENDICES, BIBLIOGRAPHY, AND INDEXA Generic Aircraft Design Flowchart 395B Example AirCONICS Code for Decode-1 399C Worked (Manned Aircraft) Detail Design Example 425C.1 Stage 1: Concept Sketches 425C.2 Stage 2: Part Definition 429C.3 Stage 3: “Flying Surfaces” 434C.4 Stage 4: Other Items 435C.5 Stage 5: Detail Definition 435Bibliography 439Index 441