Final Report Compressed

School of Mechanical Engineering

Final Year Project 2009

DESIGN AND BUILD OF AN

AUTONOMOUS HOVERCRAFT FOR

LANDMINE DETECTION

Authors:

Reuben Brown

Beau Krieg

Rahim Kurji

Paul Hocking

Adrian McLay

Jarrad Norton

Supervisor:

Dr. Maziar Arjomandi

October 30, 2009

ii

Executive Summary

This report outlines the development of a autonomous hovercraft platform for the express purposes

of land mine detection. Design, construction and testing was undertaken by a group of six final year

engineering students from the School of Mechanical Engineering at the University of Adelaide, during

2009. The aim of this project was to develop a prototype vehicle that would provide a proof of concept

for the application of hovercraft to mine detection. The scope of this project included an extensive

manufacturing effort ranging from woodworking to composite manufacture. This manufacturing was

partaken by the group, and supported by the Mechanical Engineering Workshop.

The application of a hovercraft to mine detection offers several advantages over established mine

detection methodologies. The low pressure footprint of of a hovercraft minimises the probability of

detonation. The application of autonomous features to the platform, including way point navigation

and automated mine detection and marking, removes the operator from the field and hence from the

hazard.

This unique solution however, raises a series of challenges, including the minimisation of metallic

components, designing a highly controllable yet manoeuvrable craft and successfully integration of

sensitive sensor configurations. To meet these challenges, a hovercraft configuration with a axial fan

lift system feeding a segmented skirt and a differential and vectored thrust system mounted on a

composite base structure, was designed. Autonomy was incorporated by adapting a commercially

available autopilot for use as a two-dimensional planar control system which was integrated with the

hovercrafts actuation systems via a microcontroller.

Off the self metal detector coils integrated into the hull provided detection capabilities for the platform.

The output from each coil was extracted and processed to provide a signal that could be used to

actuate a physical marking system, specifically designed to paint the ground with a high visibility

mark within a one metre halo radius of the target. This sensor configuration had a tested accuracy of

68% in detection of a representative target.

Performance testing of the hovercraft confirmed that design specifications were met. Unfortunately,

due to time constraints, full autonomy was not realised, however the detailed design and integration

provides promising groundwork for future work, with active yaw control implemented. Testing of all

other systems confirmed their suitability for the application, however the complete prototype was not

tested under the entire operational scenario at the completion of this project and is reserved for future

work.

iii

Acknowledgements

The authors of this report would like to formally recognise the valued contribution of numerous parties,

without whom this project would not have reached its current state. In particular, Project Hover would

like to formally acknowledge the Defense Science and Technology Organisation, for its financial and

technical support that made this project possible. In particular, we thank Canicious Abeynayake

and the staff at Object Detection Technologies Weapons Systems Division for their support and

expertise.

In addition, the authors would like to thank AMCOR and Soil Testing Services for their financial

support of this project.

The authors would also like to express their appreciation to this projects supervisor, Dr Maziar

Arjomandi, not only for his expertise, but also for the genuine interest he has taken in our education.

Finally, the authors would like to tank the Mechancial Engineering Academic and Workshop staff for

their interest and advice, as well as the administrative staff who made our life that much easier.

iv

Disclaimer

We, the authors, declare that the material contained with this report is entirely our own, unless

otherwise specified.

Reuben Brown a1132198

........................

Beau Krieg a1132286

........................

Rahim Kurji a1126547

........................

Paul Hocking a1132751

........................

Adrian McLay a1118636

........................

Jarrad Norton a1147683

........................

Contents

Executive Summary ii

Acknowledgements iii

Disclaimer iv

Table of Contents viii

List of Figures xiii

List of Tables xvi

Nomenclature xviiAcronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviiList of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviiList of Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviiiList of Subscripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix

Coordinate System xix

1 Introduction 11.1 Aims . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Project Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.1 Primary Project Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2.2 Extended Project Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.3 Project Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.3.1 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.3.2 Operational Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.3.3 Operational Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.3.4 Performance Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.4 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2 Feasibility Study 112.1 Hovercraft Benchmarking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.2 Landmines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.2.1 Detection Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152.3 Autonomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3 Conceptual Design 193.1 Preliminary Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.1.1 Statistical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.1.2 Beam Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.1.3 Planform Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.1.4 Weight Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.2 Prototype Developement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.2.1 Integrated Lift and Thrust Systems . . . . . . . . . . . . . . . . . . . . . . . . 223.2.2 Thrust Dominant System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.2.3 Independant Thrust Lift Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 233.2.4 Prototype Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.2.5 Prototype Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263.2.6 Prototype Specific Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.3 Power Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.3.1 Lift Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.3.2 Propulsion Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

v

vi CONTENTS

3.3.3 Preliminary Thrust and Power Estimates . . . . . . . . . . . . . . . . . . . . . 293.4 Planform Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313.5 Payload Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.6 Landmine Detection Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3.6.1 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333.6.2 Sensor Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.7 Static Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373.7.1 Application of Jupe Skirt to Enhance Stability . . . . . . . . . . . . . . . . . . 40

4 Detailed Design 434.1 Payload Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.1.1 Sensor Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454.1.2 Sensor Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474.1.3 Signal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534.1.4 Physical Marking System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

4.2 Lift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554.2.1 Design Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554.2.2 Design Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554.2.3 Fan Design and Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564.2.4 Engine Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584.2.5 Inlet Bell Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614.2.6 Mount Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624.2.7 Shaft Extension Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634.2.8 Design Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

4.3 Propulsion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644.3.1 Design Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644.3.2 Configuration Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664.3.3 Propeller Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674.3.4 Motor Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704.3.5 ESC and Battery Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714.3.6 Mount Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

4.4 Structural . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 804.4.1 Primary Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 804.4.2 Design Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 814.4.3 Specific Loading Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 824.4.4 The Sandwich Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 824.4.5 Skin Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844.4.6 Core Selcetion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904.4.7 Design Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

4.5 Skirt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 984.5.1 Design Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 994.5.2 Configuration Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 994.5.3 Material Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1044.5.4 Template Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

4.6 Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1134.6.1 Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1134.6.2 Sensors and Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164.6.3 Yaw Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

4.7 Navigation System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1254.7.1 Selection Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1254.7.2 Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264.7.3 Autopilot Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1304.7.4 Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

4.8 Platform Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1364.8.1 Platform Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1364.8.2 Trim and COG Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

CONTENTS vii

5 Manufacturing 1395.1 Manufacturing Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1395.2 Lift System Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1405.3 Inlet Bell Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1405.4 Propulsion System Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1415.5 Hull Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1435.6 Skirt Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1445.7 Fairing Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1455.8 Final Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

5.8.1 Lift System Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1465.8.2 Propulsion System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1475.8.3 Payload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1475.8.4 Skirt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1485.8.5 Fairing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

5.9 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

6 Testing 1516.1 Component Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

6.1.1 Metal Detector Range Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 1516.1.2 Metal Detector Signal Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1536.1.3 Landmine Detection Operational Scenario Testing . . . . . . . . . . . . . . . . 154

6.2 System Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1566.2.1 Lift System Airflow Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1566.2.2 Propulsion System Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1586.2.3 Static Hover Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

6.3 Longnitudinal and Transverse Behaviour Testing . . . . . . . . . . . . . . . . . . . . . 1626.4 Performance Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

6.4.1 Acceleration Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1636.4.2 Deceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1656.4.3 Additional Acceleration Performance Testing . . . . . . . . . . . . . . . . . . . 1666.4.4 Climb Gradient Tesing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1666.4.5 Additional Functionality Testing . . . . . . . . . . . . . . . . . . . . . . . . . . 1666.4.6 Turning circle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

7 Project Management and Finance 1697.1 Practical Project Management Methodology . . . . . . . . . . . . . . . . . . . . . . . . 1697.2 Resource Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

7.2.1 Organisational Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1717.2.2 Work Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

7.3 Review Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1727.4 Time Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

7.4.1 Deadline Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1727.5 Risk Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1727.6 Finance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

7.6.1 Sponsorship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1747.6.2 Financial Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1747.6.3 Labour Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

8 Conclusions 1778.1 Primary Project Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

8.1.1 Extended Project Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1798.2 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

References 180

Appendix A Autopilot Configuration Files 187

viii CONTENTS

Appendix B Segmented Skirt Stability Equations 197

Appendix C Simulink 199

Appendix D External Milestones 201

Appendix E Internal Time Line 203

Appendix F Lift Calculations 205

Appendix G Lift Mount Strength Calculations 207

Appendix H Hull Appendices 209

Appendix I Bill Of Materials 217

Appendix J Manufacturing Drawings 221

Appendix K Risk Treatment 261

Appendix L Centre of Gravity Calculations 269

Appendix M Landmine Detection Code 271

Appendix N Landmine Statistical Analysis 273

Appendix O Landmine Detection Sensors 275

Appendix P Breakdown of Hours and Costs 281

Appendix Q Sensitivities of Lift and Thrust 283

List of Figures

1 Coordinate System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi

1.1 Mission Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1 Hovertechnics HoverJet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2 AirCommander AC4 Hovercraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.3 Amphibious Marine Vanguard 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.4 Pacific Hovercraft Slider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.5 AT Landmine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.6 AP Landmine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.7 Using a probe for landmine detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.8 Vehicle mounted landmine sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.9 Autonomous Vehicle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.10 Automated Turf Management Vehicle . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.1 Beam Ratio Histogram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.2 Linear Regression Model for Dry Weight Estimation . . . . . . . . . . . . . . . . . . . 21

3.3 Splitter Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

3.4 Prototype 1 and Prototype 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.5 Prototype 3 and Prototype 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.6 Sensitivity of Lift Power to Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.7 Sensitivity of Thrust to Weight and Terrain Slope . . . . . . . . . . . . . . . . . . . . 30

3.8 FBD of Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.9 Skirt drag over different terrains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.10 Planform Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.11 Hovercraft hull showing front and rear payload bays . . . . . . . . . . . . . . . . . . . 33

3.12 Simulation landmine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.13 Change in area due to cushion deformation in pitch motion . . . . . . . . . . . . . . . 39

3.14 Reaction arm of segmented skirt in pitch motion . . . . . . . . . . . . . . . . . . . . . 39

3.15 Reaction arm of segmented skirt in roll motion . . . . . . . . . . . . . . . . . . . . . . 40

3.16 Weight vector from picth or roll motion . . . . . . . . . . . . . . . . . . . . . . . . . . 40

4.1 Dimensioned Front and Rear Payload Areas . . . . . . . . . . . . . . . . . . . . . . . . 44

ix

x LIST OF FIGURES

4.2 Required Detection Width Based on Hovercraft Dimensions . . . . . . . . . . . . . . . 45

4.3 DSTO Metal Detector Array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

4.4 Bounty Hunter Tracker IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

4.5 Dual Metal Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

4.6 Composite Metal Detector Mount Design . . . . . . . . . . . . . . . . . . . . . . . . . 50

4.7 Switching Impulse Interference Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

4.8 Metal Detector Switching Dead Period . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

4.9 Scanning Pattern With Periodic Switching . . . . . . . . . . . . . . . . . . . . . . . . . 52

4.10 Relay Circuit Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

4.11 Implemeted Threshold Levels for Landmine Detection . . . . . . . . . . . . . . . . . . 53

4.12 Marking System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

4.13 Marking System Actuation Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

4.14 Fan Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

4.15 Engine Power Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

4.16 Inlet Bell Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4.17 Diagram of Inlet Bell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4.18 Duct Diameter vs r/d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

4.19 Fan and Engine Mount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

4.20 Engine Shaft Extension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

4.21 Assembly of Mount with Inlet Bell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

4.22 Air Jet Vectoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

4.23 Air-Screw Vectoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

4.24 CT estimatation curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

4.25 Selected Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

4.26 CP estimatation curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

4.27 Typhoon 600-43 HET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

4.28 Dual DualSky 90A brushless controller . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

4.29 3800 mAh 8 cell LiPo battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

4.30 General Propulsion Mount Configuration . . . . . . . . . . . . . . . . . . . . . . . . . 74

4.31 ANSYS Analysis of Propulsion Deflection . . . . . . . . . . . . . . . . . . . . . . . . . 75

4.32 SKF Composite Bushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

4.33 Ocean Controls Stepper Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

4.34 Ocean Controls Stepper Motor Controller . . . . . . . . . . . . . . . . . . . . . . . . . 77

4.35 Propulsion System Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

LIST OF FIGURES xi

4.36 Area Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

4.37 Specific Loading Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

4.38 Weight, Strength and Stifness in Sandwitch Panel . . . . . . . . . . . . . . . . . . . . . 83

4.39 Force Distribution in a Sandwich Panel . . . . . . . . . . . . . . . . . . . . . . . . . . 84

4.40 Density Vs Tensile Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

4.41 Density Vs Tensile Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

4.42 Laminate Impact Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

4.43 Tensile Strength and Tensile Modulus . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

4.44 Flexural Ridigity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

4.45 Weight Per Ply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

4.46 Comparitve Weight for Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

4.47 Density and Compressive Modulud . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

4.48 Density and Shear Modulud . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

4.49 Density and Compressive Modulud . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

4.50 Loading 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

4.51 Weight and Deflection of R80 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

4.52 Rib-Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

4.53 Bag Skirt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

4.54 Finger Skirt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

4.55 Bag and Finger Skirt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

4.56 Pericell Skirt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

4.57 Skirt Attachment Bracket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

4.58 Bi-conical Skirt Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

4.59 Skirt attachment bracket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

4.60 Skirt attachment bracket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

4.61 Skirt Test Rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

4.62 Skirt configuration arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

4.63 Propulsion moment during operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

4.64 Jupe Template Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

4.65 Control System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

4.66 MiniDragon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

4.67 Remote and Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

4.68 Servo Pulse Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

4.69 Voltage Divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

xii LIST OF FIGURES

4.70 Stepper Control Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

4.71 Stepper Driver Signal Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

4.72 Yaw Control Prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

4.73 Yaw Prototype Closed Loop Response . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

4.74 Gyro Step Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

4.75 Closed Loop Yaw Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

4.76 Tiny Autopilot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

4.77 Kestrel Autopilot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

4.78 Microbot APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

4.79 Ardupilot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

4.80 Carrot Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

4.81 Torrens Parade Ground Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

4.82 Yaw Angle Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

4.83 3 View Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

5.1 Bell Manufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

5.2 Hull Mould . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

5.3 Hull Glassing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

5.4 Hull Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

5.5 Top Lip, Top Plate and Rib System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

5.6 Fully Assembled Platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

6.1 Test apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

6.2 Metal detector vertical range testing results . . . . . . . . . . . . . . . . . . . . . . . . 152

6.3 Metal detector range horizontal testing results . . . . . . . . . . . . . . . . . . . . . . . 152

6.4 Signal testing apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

6.5 Periodic switching interference and positive signal . . . . . . . . . . . . . . . . . . . . 154

6.6 Positive detection and Object Interference Levels . . . . . . . . . . . . . . . . . . . . . 154

6.7 Operational landmine detection scenario . . . . . . . . . . . . . . . . . . . . . . . . . . 155

6.8 Detection accuracy over hovercraft width . . . . . . . . . . . . . . . . . . . . . . . . . 155

6.9 Landmine physical marking results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

6.10 Volumetric flow rate as a function of RPM and efficiency . . . . . . . . . . . . . . . . . 157

6.11 Thrust Testing Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

6.12 Thrust Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

6.13 Local Coordinate System for Static Hover Test . . . . . . . . . . . . . . . . . . . . . . 160

LIST OF FIGURES xiii

6.14 Static Hover Test Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

6.15 Variation is drift due to lift engine speed . . . . . . . . . . . . . . . . . . . . . . . . . . 162

6.16 Longintudinal and Transverse Response . . . . . . . . . . . . . . . . . . . . . . . . . . 163

6.17 Acceleration over 5 m intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

7.1 Organisational Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

7.2 Expenditure and Monthly Breakdown . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

7.3 Monthly Breakdown of Hours Spent . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

M.1 Landmine detection code, main method . . . . . . . . . . . . . . . . . . . . . . . . . . 271

M.2 Landmine detection code, timer interrupt . . . . . . . . . . . . . . . . . . . . . . . . . 272

O.1 Basic GPR operation diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276

O.2 GPR pulse detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277

O.3 Metal detector coil operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278

O.4 Detection range for 9 inch coil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279

Q.1 Sensitivity of Lift Power to Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284

Q.2 Sensitivity of Thrust to Weight and Terrain Slope . . . . . . . . . . . . . . . . . . . . 286

Q.3 Sensitivity of Thrust to Head Wind Speed . . . . . . . . . . . . . . . . . . . . . . . . . 287

Q.4 Effect of Mass of Propulsion Power Requirements . . . . . . . . . . . . . . . . . . . . . 287

This Page Intentionally Left Blank

List of Tables

1 Coordinate Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi

1.1 Summary of Performance Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.1 Pearson Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.2 Beam Ratio Descriptive Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.3 Landmine detection sensor decision matrix . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.1 Front payload bay specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.2 Bounty Hunter Tracker IV specifications . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.3 Metal Detector Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.4 Fan Types and Characteristics (Bleier, 1997) . . . . . . . . . . . . . . . . . . . . . . . 56

4.5 Fan Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

4.6 HGA-100L Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

4.7 KT100J Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

4.8 Engine Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

4.9 Skirt Configuration Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

4.10 Skirt Configuration Comparison, Adapted from (Fitzgerald and Wilson, 1995, pg. 12)

& (Amyot, 1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

4.11 Elastomer Material Comparison, Adapted from (Amyot, 1989) . . . . . . . . . . . . . 105

4.12 Fabric Material Comparison, Adapted from (Amyot, 1989) . . . . . . . . . . . . . . . . 105

4.13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

4.14 Summary of Inputs and Outputs for Microcontroller . . . . . . . . . . . . . . . . . . . 115

4.15 Selection Criteria for Autopilot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

4.16 Tiny v2 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

4.17 Kestrel Autopilot Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

4.18 Microbot APS Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

4.19 Ardupilot Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

6.1 Propeller thrust output at 75% throttle . . . . . . . . . . . . . . . . . . . . . . . . . . 158

6.2 Drift Results for Trim Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

6.3 Drift response to lift engine speed during static hover . . . . . . . . . . . . . . . . . . 162

6.4 Acceleration Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164

xv

xvi LIST OF TABLES

6.5 Theoretical Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164

6.6 Deceleration performance of the hovercraft . . . . . . . . . . . . . . . . . . . . . . . . . 165

7.1 Financial Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

D.1 External Milestones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

E.1 Internal Time line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

O.1 List of current landmine senor types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

O.2 Various magnetometer types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277

P.1 Hours and Costs Breakdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281

Nomenclature

Acronyms

AP Anti Personnel. 14, 38

AT Anti Tank. 14, 38

ATD Analog to Digital. 121

BOM Bill of Materials. 225

COG Centre of Gravity. 78, 145

CPT Cure Ply Thickness. 94

CPU Central Processing Unit. 135

DGPS Differential GPS. 17, 18, 133, 137

ESC Electronic Speed Controller. 76

FBD Free Body Diagram. 34

FVF Fibre Volume Fraction. 93, 94

FWF Fibre Weight Fraction. 94

GPL GNU Public License. 134

GPR Ground Penetrating Radar. 39, 245, 246

GPS Global Positioning System. 4, 17, 18, 120,133, 135137, 139, 141, 176, 178, 191

GRP Glass Reinforced Plastics. 87

GUI Graphical User Interface. 4

I2C Inter-Integrated Circuit. 135, 144

ICT Input Capture Timer. 121

IMU Inertial Measurement Unit. 17, 18, 120,133, 135, 136

KF Kalman Filter. 17, 18, 133

LiPo Lithium Ion Polymer. 76

MCU Microcontroller. 56, 59, 76, 121, 133, 144

MOI Moment of Inertia. 81

OS Operating System. 139

PC Personal Computer. 133

PID Proportional Integral Derivative. 126, 138

PWM Pulse Width Modulation. 134137

RC Remote Control. 72, 74, 126, 189

RPM Rotations Per Minute. 72

SOP Safe Operating Procedure. 184, 185

SPI Serial Peripheral Interface. 135, 144

UAV Unmanned Aerial Vehicle. 133, 135

UN United Nations. 14, 48

VLF Very Low Frequency. 49, 50

List of Symbols

J Advance Ratio.

Angle.

A Area.

B Beam Length.

C Coefficient.

S Characteristic Coefficient.

D Loss Coefficient.

Density.

Wd Design Weight.

T Thrust.

D Diameter.

xvii

xviii List of Units

DA Aerodynamic Drag.

DC Cushion Momentum Drag.

DS Skirt Interaction Drag.

DT Terrain Slope Drag.

e(t) Error Term.

Q Volumetric Flow Rate.

W Force of Engine on Each Support.

L Lift Force.

g Acceleration due to gravity.

h Hover Height.

Ixp Moment of Inertia (Propulsion).

Deflection.

C Circumference.

H Height.

a Characteristic Length.

b Characteristic Length.

d Characteristic Length.

h Characteristic Length.

s Characteristic Length.

y Characteristic Length.

L Length.

t Thickness.

M Mass.

M moment.

I Moment of Inertia.

N Number of Fan Blades.

Pd Pitch to diametre ratio.

Pitch Angle.

Pitch Angle.

XMP Pitch Moment Arm.

P Power.

P Pressure.

R Radius.

Roll Angle.

n Rotation Speed.

Skirt Contact Angle.

E Elastic Modulus.

V Velocity.

List of Units

degrees (rotation).

Hz Hertz.

HP Horse Power.

h hour.

k kilo.

mAh Milli-amp Hours.

m metre.

min minute.

ms millisecond.

Pa Pascals.

rpm Revolutions per Minute.

s second.

V Volt.

List of Subscripts xix

W Watt.

List of Subscripts

a Air.

B Beam.

cg Centre of Gravity.

c Cushion.

d Drag.

R Fan Ring.

f Footprint.

gen Generated.

H Hover.

hc Hovercraft.

L Lift.

max Maximum.

NET Net.

b Per Blade.

p pivot.

p Planform.

P Power.

p Propeller.

r Ratio of air to total pressure requirement.

st Skirt.

t Theoretical.

T Thrust.

ts T Section.

Coordinate System

The coordinate system and reference frames described in the figure and table below will be the con-

ventions used throughout this report.

Figure 1: Coordinate System

Table 1: Coordinate SpecificationsMotion Force or Linear or Position or

Moment Angular Velocity Euler AngleSurge X u xSway Y v yHeave Z w zRoll K p Pitch M q Yaw N r

xxi

Chapter 1

Introduction

1.1 Aims

There are over 100 million buried and active land mines across the world today. Hundreds of millions

more are stored in military stockpiles, and over 10 million more are produced annually. Land mines

and explosive remnants of war affect at least 78 countries and injure or kill up to 20,000 people

annually. Land mines, cluster bombs and unexploded ordinance provide a real and enduring threat

for local populations, wildlife and ecosystems. There is a need to develop a method of detection which

is sustainable, has low environmental impact and is of low risk to human life.

There are currently several techniques of mine and unexploded ordinance detection which require

time consuming, manual surveying of potential minefields. These methods include human screening,

placing an operator at extreme risk, or effective vehicle mounted/destructive methods causing extreme

environmental damage through the detonation of mines. This project proposes the use of an unmanned

hovercraft as a mounting platform for mine detection technologies. A hovercraft is less likely to initiate

pressure sensitive munitions as it has a low ground pressure footprint. Furthermore, autonomous

features will remove the operator from the minefield and the threat. Environmental damage through

the travel of the craft will be significantly reduced from traditional vehicle mounted methods.

There are several design issues which will need to be targeted specifically in the design of this platform.

Maneuverability and controllability of the craft are important and detection and detonation cannot be

performed by the same platform a degree of accuracy will be required in order to mark the positions

of detected bodies. This in itself raises several issues which need to be addressed through design. Any

horizontal drift of the craft will need to be kept to a minimum to ensure a desired orientation can be

maintained. Accurate turning and motion capabilities will also be required. Furthermore, the effects

of cambered or sloped terrains on the crafts direction of travel may need to be compensated for. A

marking system will need to be devised which identifies the location of any detections and alerts the

operators to these finds. Current mine detecting sensor arrays are quite heavy and expensive, and thus

the hovercraft should be capable of lifting a payload of sensors which must be isolated from potential

damage. Similarly the hovercraft is required to hover at a height which optimises the performance of

1

2 CHAPTER 1. INTRODUCTION

these sensors.

The design considerations which come about through the application of a hovercraft to this function

lead to a set of primary objectives for the platforms development.

1.2 Project Objectives

The following section outlines the objectives to which this project aims. These objectives are classified

as either primary or extended, dependent on their difficulty and scope.

1.2.1 Primary Project Objectives

Primary project objectives benchmark the minimum outcomes that should be achieved for the project.

1. To design and manufacture a remotely controlled hovercraft

Outline:

The project group will design and manufacture a remote controlled, unmanned hovercraft to the

specifications outlined in Section 1.3.4.

Measure of Completion:

Testing will be composed of a variety of test flights designed to assess the performance of the

craft across the performance parameters outlined in Section 1.3.4. A linear run will be used to

assess the acceleration, operational speed and deceleration performance of the craft. Turning

radius will be assessed using a u-turn maneuver, and extended flight tests will be used to

confirm the endurance of the craft. Successful completion of this goal will be achieved when all

design parameters (Table 1.1) are physically tested and confirmed.

2. To provide adequate control and stability to the hovercraft such that it can hover

while stationary.

Outline:

Control and stability mechanisms, will be designed such to limit the horizontal drift of the

hovercraft to within a halo radius of two metres.


The hovercraft will be tested under the static hover scenario to ensure that it will remain within

1.2. PROJECT OBJECTIVES 3

a 2 metre halo radius of its starting position for at least 30 seconds. The hovercraft will be

tested indoors, away from any significant external airflow and on a flat, level surface.

3. To manufacture a hovercraft to accommodate an off-the-shelf metal detector array

Outline:

Control and stability mechanisms must be adequate enough to accommodate the limitations of

the sensor. Furthermore, the platform must have sufficient means to function with a payload of

20kgs.


The sensor will be installed and tested by placing a target within the sensors line of sight as

it traverses a linear path. Should the hovercraft be able to perform all of the functionalities

outlined in objectives 1 and 2 while under payload, this objective will be declared complete.

4. Hovercraft must be able to identify and physically mark the location of mines.

Outline:

The completed hovercraft, with installed payload, will be able to identify a target representing

a land mine. When the hovercraft passes over the mine it will leave a physical mark within a 1

metre halo radius of the target.


The completed hovercraft will be set on a linear path whereby it will pass over a target repre-

senting a land mine. By completion of its run, it will be required to leave a physical mark within

a 1 metre halo radius of the target.

1.2.2 Extended Project Objectives

Extended project objectives represent an increased project scope that will compliment and enhance,

but not define the project.

1. The hovercraft will autonomously follow a predefined path over flat terrain with no

obstacles

Outline:

Provision will be made as a part of the control system, for the hovercraft to follow a predefined


path, based on Global Positioning System (GPS) feedback. The path will be over flat terrain,

with no obstacles.


A basic path though a field composed of straight lines and u-turns, will be predefined and

uploaded to the hovercrafts host. Upon activation of the hovercrafts automatic control systems,

the GPS location of the hovercraft will be continuously recorded and compared to the desired

path to access the precision between the two.

2. GPS tracking of the hovercraft combined with graphical user interface

Outline:

An installed GPS on the hovercraft will be utilised such that the location of the hovercraft may

be tracked remotely, in real time, via a Graphical User Interface (GUI).


The hovercraft will be manually navigated around a large course, across a predefined track.

During the test, the GPS data will be streamed in real time to produce a comprehensive account

of the hovercrafts position for the duration of the test. The same track will then be traversed,

by foot, with a hand held GPS to produce a series of way points along the path. Both points

will then be compared for precision. Successful completion requires that the GPS measurements

be within 2 times the accuracy of the least accurate system.

3. Electronically mark the position of mines

Outline:

Positive responses from the payload sensors will be recorded electronically, in real time, using

GPS co-ordinates.


Targets will be manually placed around a field, and their GPS co-ordinates recorded using a

hand held GPS unit. The hovercraft will then be remotely controlled such that the sensors pass

over the target mines. The co-ordinates recorded by the on board GPS will be compared to the

initially recorded points to assess the precision between the two. Successful completion requires

that the GPS measurements be within 2 times the accuracy of the least accurate system.

4. Operation in non-ideal environments

1.3. PROJECT DEFINITION 5

Outline:

The hovercraft will be tested in more challenging environments including cambered, sloped and

uneven terrains, and in more challenging environmental conditions including light rain and wind

(weather dependent).


Additional test sites will be located and surveyed in terms of their environmental parameters.

The basic tests used to assess the competition of Goal 1 will be repeated within these var-

ied environments to confirm required operating performance for additional environments and

conditions.

1.3 Project Definition

1.3.1 General Requirements

This following considerations must be taken into account when designing the platform.

Sizing Restrictions

Given that this is a prototype platform, a large amount of testing will be required. In order

simplify transport, it desirable that the platform should fit entirely into the tray of small trailer,

and hence should be no larger than a 1800 by 1200 mm rectangle. Designs that maximise the

width of the sensor sweep of the craft are to be given preference.

Weight Restriction

To make transportation easier, the platform should not require additional equipment to load

and unload it from the transportation vehicle, and as such the platform, including payload, is

limited to 100 kg. Lighter designs are to be preferred to minimise power requirements and to

ease transport.

Endurance

As this is a proof-of-concept design, the prototype platform requires minimal endurance for

testing purposes. As such, a minimum endurance of 10 minutes is required for testing purposes.

Control

The hovercraft is required to be unmanned, and should be controlled by remote and operate

autonomously for some functions. Remote control should be used for testing purposes, as well

as overriding autonomy in the event that these features fail.


Hover Height

The hover height of the platform determines the height of the obstacle that the platform can

traverse, hence higher hover heights are advantageous to the application as it expands the range

of operating environments that the hovercraft can be applied to. Despite this, the hover height

is also restrained by the operating range of the sensors.

Payload

The platform should be capable of housing and operating mine detection hardware. To allow

for a range of sensors, and processing equipment, a payload capacity of 20 kg has been defined.

1.3.2 Operational Environment

Test Environment

The test environment represents the ideal operating environment for the hovercraft, that is a static

environment away from inputs that will degrade the performance of the craft in operations. This

environment expresses the simplest and minimum requirements upon which the hovercraft is required

to meet the specified performance levels. Such an environment will provide minimal drag, and as such

will be inside, on a flat, smooth concrete surface, away from wind and other weather effects. The

features of this environment include:

Inside

Negligible Slope (

1.3. PROJECT DEFINITION 7

1.3.3 Operational Scenario

Mission Profile

The mission profile for the platform will follow the process as outlined in Figure 1.1

This mission profile with be achieved using a series of modes of operations for the hovercraft.

Figure 1.1: Mission Profile

Modes of Operation

Home

Upon entering the field the initial mode should be to move to the home position


Mine Sweep

The Mine Sweep mode of the hovercraft will consist of autonomous navigation by traversing

between preprogrammed way points.

Manual Navigation

Manual, remote control of the platform will be invoked for advanced manoeuvres, such as obstacle

avoidance and course corrections, in the event that they are required.

Post-Detection

When a positive signal is received from the mine detection sensor payload, the craft will perform

the following action sequence:

1. Log GPS co-ordinates

2. Perform back-up loop to confirm the reading

3. Positive response from back-up loop initiate physical marking system

4. Negative response from back-up loop, the platform should store the GPS co-ordinates in

a list of possible positives

5. Return to Mine Sweep mode

Return Home

Upon commencement of sweep, or due to depletion of power supply, the platform should proceed

along a preprogrammed path back to the home position.

Manoeuvrability Requirements

Lift off

The hovercraft will be required to lift off the ground to the appropriate hover height.

Stationary Hover

The platform will be capable maintaining a stationary position while hovering.

Forwards

The platform will be required to accelerate to its operational speed and continue forwards while

maintaining a straight course. The operating speed is defined as walking speed, that is 4-6

km/hr as this is the operating speed of current mine detection methodologies. The platform

should accelerate to this speed within 10 seconds.

1.4. SCOPE 9

Reverse

The reverse manoeuvre is required for the hovercraft to be able to rescan a potential sensor

target, as to confirm its presence. The reverse manoeuvre is similar to the forwards manoeuvre

in that is must accelerate to operational speed (5 km/hr) and maintain a straight course.Acceleration to this speed should also be within 10 seconds.

Left and Right Turns

The platform must be capable of pivoting in yaw such that it may successfully transverse the

minefield. Tight turns are required, and hence a maximum turning radius of 2 times the craft

length is required.

Braking

The braking manoeuvre is required to bring the platform to rest from operational speed, and

into the Stationary Hover mode. Deceleration to rest should be within 10 seconds.

1.3.4 Performance Specifications

Table 1.1 summarises the performance specifications that have arisen from the various requirements

which have been discussed in this section.

Table 1.1: Summary of Performance RequirementsParameter Value

Length

Chapter 2

Feasibility Study

2.1 Hovercraft Benchmarking

In order to determine the hovercraft technology available a market study of hovercraft was undertaken

to identify different configurations implemented to date. The majority of the hovercraft looked at are

hovercraft sold for leisure or commercial purposes. Four smaller hovercraft in particular were identified

and are summarised below based on there variances in configuration. The only unmanned hovercraft

identified were small remote control hovercraft models.

Hovertechnics HoverJet

Figure 2.1: Hovertechnics HoverJet (Hovertechnics, 2009)

Hoverjet is a leisure hovercraft sold by hovertechnics and is able to seat 2 people. The hoverjet

implements a segmented skirt configuration and has integrated lift and propulsion systems. This

means that the hovercraft may only hover when moving forward. The fan is run from a rotax engine

and is of axial configuration. The hull is made of a Kevlar composite structure and the craft is able

to obtain maximum speeds of 64 k/h.

11

12 CHAPTER 2. FEASIBILITY STUDY

Figure 2.2: AirCommander AC4 Hovercraft (Air-Commander, 2009)

AirCommander AC4 Hovercraft

The AirCommander AC4 is used as a firefighting hovercraft and is principally designed to traverse

water and swampy regions. The lift and propulsion system of this hovercraft are independant meaning

the hovercraft can hover while stationary, and run off independant motors. As can be seen in Figure

2.2 the lift fan is installed into the front of the hovercraft and propulsion at the rear. The AC4 again

implements a segmented type skirt configuration and uses a composite hull. Tis hovercraft is able to

seat 4 persons and lift a 1 tonne payload.

Amphibious Marine Vanguard 14

Figure 2.3: Amphibious Marine Vanguard 14 (Amphibious, 2009)

The Vanguard 14 by Amphibious Marine is a 3-4 persons hovercraft capable of lifting a 350 kg payload.

2.2. LANDMINES 13

THe craft structure is primarily a composites, aluminium hybrid, with aluminium being used to mount

engines. The thrust and lift are again independant systems, and a ducted fan is used as propulsion

vectored using rudder control surfaces. The Vanguard 14 implements a segmented bag type skirt

which is made up of 4 main compartments (fore, aft, port and starboard). The front bag is able to be

dropped to cause a drag and effective braking of the craft.

Pacific Hovercraft Slider

Figure 2.4: Pacific Hovercraft Slider (Pacific-Hovercraft, 2009)

Finally the slider by Pacific Hovercrafts is a New Zealand made vehicle and implements a bag and

finger type skirt. It is the only small hovercraft benchmarked under 4 m length to do so. Although

there is only one motor (does not have mechanical isolation), the lift and thrust systems run off

independant fans. Two centrifugal fans are used for lift and an axial fan for thrust. This hovercraft is

able to obtain max speeds of 80 k/h and has been utilised in military applications. Its average payload

capacity is 275 kg with a length to beam ratio of 1.8.

2.2 Landmines

It is estimated there are currently more than 100 million active landmines around the world, with 100

million more in storage (Bruschini and Gros, 1998). Of these there are more than 350 known land

mine designs, varying in weight, size, material and power (Unicef, 2000). Landmine statistics have

indicated over 65 effected countries around the world. Landmines are responsible for approximately

26,000 deaths worldwide, per year; half of which are caused from severe injuries, before the victim is

found or taken to hospital (Buse, 1999).

The cost to deploy a landmine can vary between $3 and $30, whist is can cost up to $1000 to remove

a single landmine (Products, 2007). It is estimated it would cost a minimum of 33 billion dollars to


remove all currently active landmines and at the current removal rate it would take over 1000 years.

The United Nations (UN) have set detection goal of 99.6% for the detection and removal accuracy of

landmines and a false alarm rate of one every 1.25 square meters. Currently no detection methods are

capeable of acheiveing these standards. This is due to a number of factors such as varying landmine

types, environmental conditions and technology limitations (Office, 2001).

Operational landmines are normally buried in the first 300 mm of soil and are found in all open terrain

types (Stull, 1997). Buried landmines are most often pressure activated and often have an alternate

firing mechanism . Landmines types can typically be classified into two categories, Anti Tank (AT)

mines and Anti Personnel (AP) mines, also referred to as blast mines and fragmentation mines,

respectively.

AT mines, as their name suggests, are target towards tanks and vehicles and are commonly found

in open areas such as roads and fields. They are typically the larger of the two mines and contain

significant explosive content, having an average weight and diameter of approximately 10 kg and

280mm, respectively (Figure 2.5). AT mines are most commonly activated using a pressure trigger,

requiring an activation pressure in the order of 100s of kg to detonate (Das et al., 2002).

Figure 2.5: Physical composition of an AT landmine (HowStuffWorks, 2009) and (Gudmundson, 2008)

AP mines, targeted towards humans, are far smaller than AT mines, often found in dense environ-

mental locations such as scrub and walking trails. AP mines not only contain explosive content but

metallic fragments, used as high speed projectiles (Figure 2.6). They may be triggered from a number

of high sensitivity activation mechanisms such as a tripwire, sound levels and pressure.

The landmines detailed above are considered traditional landmines, laid post World War 2 and are

made mainly from metallic components. More recent technology has lead to the invention of composite

landmines, which contain little to no metallic components making them incredibly difficult to detect.

2.2. LANDMINES 15

Figure 2.6: Physical composition of an AP landmine (HowStuffWorks, 2009) and (News, 2009)

2.2.1 Detection Methods

Direct Detection

Direct detection traditionally involves a human operator physically searching through the minefield

(Figure 2.7). This is one of the slowest and most expensive methods of landmine detection, costing

approximatley $1000 and taking up to four hours to remove a single landmine. Further it is the most

dangerous form of detection, resulting in one death for every 1800 mines that are removed (Bruschini

and Gros, 1998).

Figure 2.7: Officer using a probe for landmine detection (Wikipedia, 2009)

Subsequent forms of direct detection involve an operator with a metal detector or another form of

landmine detection sensor, such detection methods are quicker than a probe, but are less accurate

and still place the operator in great danger. More abstract direct detection methods use animals,

such as dogs, ferrets, rats and bees to detect the explosive content in landmines. Animals are highly

accurate for specific landmine types and environmental conditions, but are extremely expensive and


time consuming to train.

Mechanically Assisted Detection

Vehicle mounted sensors are the primary form of direct detection (Figure 2.8). Vehicle mounted sensors

are far larger and heavier than hand held sensors and provide a considerably increased ground coverage

(Gooneratne et al., 2004). These methods produce a great risk of premature detonation, placing the

equipment and more importantly the operator at risk. Such methods are also very expensive.

Figure 2.8: A vehicle mounted landmine detection sensor (qsine, 2005)

More severe mechanical methods aim to detonate landmines, rather than detect them. The most

common method of vehicle landmine detonation is a front mounted flail. A flail operates from a

number of large metal balls mounted on the end of a chain and subsequently to a rotating axle, that

are used to pound the ground and trigger any landmines. This method is one of the most accurate

and fastest forms of landmine deactivation, however results in significant environmental damage.

2.3 Autonomy

Kelly et al. (2006) designed and built an autonomous vehicle to operate in a challenging environment

and also to map an area following a predefined path, consisting of multiple way points (Figure 2.9).

The sensors used were odometry sensors, Differential GPS (DGPS), ground speed radar and an Inertial

Measurement Unit (IMU). These sensors are input into a Kalman Filter (KF) to provide accurate state

estimates. In order to incorporate obstacle avoidance, the vehicle also used 2D scanning ladars, stereo

cameras, infrared cameras and a pressure sensitive bumper. To process all the input data the vehicle

uses five commercial desktop computers, one for sensor interfacing, one for creating depth maps from

2.3. AUTONOMY 17

the stereo cameras, one to log the video which can be analysed at a later date, one for auxiliary

interfaces and one for all the actuators and low-level sensors.

Figure 2.9: Autonomous Vehicle (Kelly et al., 2006)

Roth and Batavia (2002) developed a formal method for comparing and evaluating the performance

of path tracking algorithms for their automated turf management vehicle, shown in Figure 2.10. The

design goals of the vehicle were to find small objects with no false positives, detect all true obstacles to

keep the vehicle safe, operate within cm level precision and must be able to cover area in an efficient

and effective manner. The sensors used were a GPS, IMU, stereo based homography and a laser

sensor. The combined GPS and IMU are used to determine accurate position combined with a Zhang

path tracker (Zhang et al., 1997) to move the autonomous vehicle in complex manoeuvres with little

deviation from a defined path. To avoid obstacles the stereo based homography is used to detect

objects which lie above the ground plane with the laser scanner used as a backup detection system

for instances where vision-based methods fail.

Figure 2.10: Automated Turf Management Vehicle


Mandapat (2001) developed an autonomous system for use with their navigation test vehicle and then

performed a comparison between three different configurations of IMU, GPS and KF. The first config-

uration used an expensive high accuracy DGPS and a high data rate IMU, which showed positioning

accuracy of under 10 cm at a data rate of 10 Hz. The second configuration was a GPS with ability to

measure position and orientation, which had accuracy within 20 cm at a data rate of 5 Hz. The third

configuration uses a KF on an IMU with a low cost DGPS, and then a second KF on the combined

IMU and GPS data. This configuration achieved an accuracy of 20 cm at the fastest data rate of 12.5

Hz. The IMU/GPS compares favorably in that its adequate performance and low cost makes it ideal

for autonomous ground vehicle navigation (Mandapat, 2001).

Chapter 3

Conceptual Design

3.1 Preliminary Sizing

3.1.1 Statistical Analysis

To aid in the preliminary sizing of the hovercraft, a market survey of 26 light hovercraft (less than

one tonne) was performed and their dimensional data, namely empty weight, payload weight, length

and width, was collated for statistical analysis. The Pearson correleation coefficents where calculated

for the empty, payload and total weights of the craft, as well as their length, width and beam ratios.

These results are summarised in Table 3.1.

Table 3.1: Pearson TableWE WPL WTOTAL Length (L) Width (W) L/W

WE Pearson 1 0.89275 0.96568 0.68036 0.40484 0.36366Sig. - < 0.001 < 0.001 < 0.001 0.040 0.068

WPL Pearson 0.89275 1 0.97913 0.80203 0.57483 0.36739Sig. < 0.001 - 0 < 0.001 0.002 0.065

WTOTAL Pearson 0.96568 0.97913 1 0.76922 0.51398 0.37581Sig. < 0.001 0 - < 0.001 0.007 0.058

Length (L) Pearson 0.68036 0.80203 0.76922 1 0.45559 0.68Sig. < 0.001 < 0.001 < 0.001 - 0.019 < 0.001

Width (W) Pearson 0.40484 0.57483 0.51398 0.45559 1 -0.3335Sig. 0.040 0.002 0.007 0.002 - 0.096

L/W Pearson 0.36366 0.36739 0.37581 0.68 -0.3335 1Sig. 0.068 0.065 0.058 < 0.001 0.096 -

3.1.2 Beam Ratio

As part of the market survey, the beam ratio of 26 hovercraft were sampled. Given that there was

no independant, statistically significant correlations between the beam ratio and the other deign

constraints (Table 3.1), the beam ratio can be considered an independant quantity, and hence the

use of any commonly used beam ratio is warrented. Figure 3.1 displays a frequency histogram of the

beam ratio for the sample, while the desciptive statistics are summarised in Table 3.2. The beam

19

20 CHAPTER 3. CONCEPTUAL DESIGN

1 . 0 1 . 2 1 . 4 1 . 6 1 . 8 2 . 0 2 . 2 2 . 40

1

2

3

4

5

6

Freque

ncy

B e a m R a t i o ( L / W )

Figure 3.1: Beam Ratio Histogram

Table 3.2: Beam Ratio Descriptive StatisticsN 26

Mean 1.788Standard Deviation 0.31164

Lower 95% CI of Mean 1.66182Upper 95% CI of Mean 1.91357

Minimum 11st Quartile 1.63

Median 1.83rd Quartile 2.03Maximum 2.25

ratios for the sample encompass a wide range of possible values, with possible values ranging from 1

to 2.25. Despite this, the histogram shows that the far majority of the data is grouped between 1.5

and 2.3, which is confirmed by the borders of the interquatile range. Hence, while it is possible to

design hovercrafts with a beam ratio of unity, the majority of craft have ratios higher than 1.5. This

minimum beam ratio was selected as per the requirement to maximise the possible sensor sweep of

the craft for a given craft area.

3.1.3 Planform Sizing

As per the general requirments for the platform, the entire hovercraft is required to fit in a 1800

x 1200 mm rectangle. Allowing 100 mm for the protrustion of additional equipmemnt such as the

skirt and skirt attachments, reduces the maximum planform sizing to 1700 x 1100 mm. Given the

3.1. PRELIMINARY SIZING 21

0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 00

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

Empty

(kg)

P a y l o a d ( k g )

Figure 3.2: Linear Regression Model for Dry Weight Estimation

precribed beam ratio of 1.5, width becomes the limiting factor, and a planform sizing of 1100x1650

is appropriate. The length of the hovercaft was reduced to 1600 for simplicity, given a final planform

sizing of 1600 x 1100 mm.

3.1.4 Weight Estimation

Statistical relations based on the aforementioned market survey were used as the basis for the ini-

tial weight extimation of the platform. To determine the best available predictor variable of empty

wight; payload weight, length and width were assessed for their correlation with dry weight, for a

variety of hovercraft. The corresponding Pearson correlations are summarised in Table 3.1. Both

length and payload weight display high correlations with empty weight, with Pearsons coefficients of

0.89275 and 0.68036 respectively. Both correlations are statistically significant at the 99% confidence

level(p


3.2 Prototype Developement

Four prototype designs were generated using a combination of possible systems and configurations.

These prototypes are described and assessed in this section.

Development of the overall configuration was heavily influenced by existing configurations and bench-

marking, but the unique requirements of this platform also needed to be taken into consideration.

Three major configurations were considered:

1. Integrated Lift and Thrust Systems

Lift Dominant Systems

Thrust Dominant Systems

2. Independent Thrust and Lift system

3.2.1 Integrated Lift and Thrust Systems

Lift Dominant Systems

With a lift dominant system, the craft structure is centered primarily around lift system. The primary

advantage of such a configuration is the reliability of the lift system and limited effect on pitch and

roll stability of the craft given the low moment created by an integrated thrust system.

One of the initial designs conceived was a platform build around a centrifugal fan with the integration

of puff port around the craft which could be actuated by a series of butterfly values A high daylight

clearance is more probable given the nature of the lift system and its overcall influence on the vehicle.

One of the major conceived disadvantage would be high levels of precession excepted with a dominant

centralised lift system, however with the addition of puff ports the control of the hovercraft could be

highly refined mitigating such a risk. However, exceptional levels of maneuverability would come at

the price of low levels of thrust. Limitation in operational terrain would apply and most importantly

the inability to traverse ground with variable slopes would be lost. An additional disadvantage is that

puff porting could potentially cause variations in the pressure distributions of the air cushion. This

is undesireable for the application of mine detection as if the pressure lowers enough to cause contact

with the ground there is high risk of setting off mines.

3.2. PROTOTYPE DEVELOPEMENT 23

Figure 3.3: Splitter Configuration

3.2.2 Thrust Dominant System

A vehicle designed around its thrust system can be considered to be thrust dominant. The primary

advantages of such a system are the high levels of thrust and consequently high operational velocities.

Air from the thrust system is drawn off, in most cases by installing a splitter behind the axial thrust

fans, and directed at high velocity into the plenum chamber. This principle is shown in Figure 3.3.

The primary disadvantage of this system is that the platform is unable to statically hover as thrust is

required to generate lift. Due to the operational scenarios of the hovercraft, in particular the desired

ability to stop and confirm positive detection signals, this characteristic is undesireable.

3.2.3 Independant Thrust Lift Systems

A combination of the two systems can be seen in the independant thrust lift system. In such a

configuration, no one system is dominant, allowing for better control of design variables. Although a

weight penalty must be endured for incorporating a independent systems, greater levels of reliability

and high levels of maneuverability are achieved.

An independent thrust and lift system allows for an inherent fail safe mechanism in the platform. In

the event the thrust system fails, the craft is still in hover. This is ideal for the operational environment

of the platform.


3.2.4 Prototype Generation

Some characteristics of the platform were able to be selected prior to the generation of different

configurations. It was decided initially that a skirted craft was required to maintain an acceptable

level of efficiency and controllability to the platform. This left the main prototype decisions to be

between independant and integrated lift and thrust, and the method of manoeuverability control.

Prototype 1

Prototype 1 represents a typical small hovercraft design in that a single, large, engine and fan is used

to provide both lift and propulsion. The flow from the single ducted fan is split into two streams,

generally using a splitter plate, with approximately one third of the flow being redirected in the plenum

chamber to generate lift. The remaining flow is used for propulsion. Control of the craft is provided

by rudders to adjust the direction of the thrust vector and cause a torque in yaw. The design is skirted

to increase stability and efficiency of the craft.

Prototype 2

Prototype 2 incorporates three fans and engines, one for lift and the other two for propulsion. The

lift fan is the standard horizontally orientated, axial fan and petrol engine combination. The two

propulsion sources are electric motor controlled propellers free to rotate around the vertical axis to

provide vectored thrust. These two fans are positioned at the aft edges of the craft, and each system has

two degrees of freedom, angular position and throttle. This configuration boasts high manoeuvrability

and the ability to move in reverse and brake.

Prototype 3

Prototype 3 was used to demonstrate the possibility of differential thrust as a control mechanism. The

dual hull configuration has unecessary complexity in that two skirts and two air sources (or splitting

of one source) is required to achieve lift. The main disadvantages of this design is stability analysis

of the platform becomes complex and as the cushion does not cover the entire area of the platform,

pressures may exceed the limit for preventing the detonation of landmines.


Figure 3.4: Prototype 1 and Prototype 2

Figure 3.5: Prototype 3 and Prototype 4


Prototype 4

Prototype 4 implements integrated lift and thrust systems by using a single, horizontally orientated

axial fan and engine combination. The outlet air from this system is split, with part of the flow

being directed into the air cushion as lift. The remaining flow is fed into a duct network with several

fixed outlets positioned around the perimeter of the craft. Each of these outlets have variable valves

attached to them to vary the output thrust from each. Selective operation of these valves relative

to each other allows the hovercrafts net thrust vector to be manipulated for propulsion and control

of the craft. The main disadvantage of this system is that difficult control strategies are required to

achieve control with so many variables, and an accumulator may be required to maintain sufficient

pressures in the piping for thrust.

3.2.5 Prototype Selection

The dominating factor for the selection of lift and thrust system integration was the ability to statically

hover. Static hover is defined as a necessary component of performance to achieve the operational

requirements of the platform. It was therefore selected to use independant lift and thrust systems and

account for extra weight requirements.

Manoeuvrability Control Mechanism

Three primary methods of manoeurability control were recognised

Rudder & Elevon Configurations

Control surface maneuvrability, as implemented on conventional aircraft, is inefficient at low speeds

(Amyot, 1989). Implementation on a hovercraft therefore requires installation within the slip stream

of a propeller or air jet. There are two main control surfaces implemented on hovercraft, rudders

and elevons. Rudders are used for controlling the hovercraft in yaw and allow the generation of a

turning moment through the redirection of the thrust. Rotation of the rudder surface effects this

force. Elevons work on the same principal as rudders however are orientated horizontally to create a

moment in the direction of pitch (Bliault and Yun, 2000). They are primarily used to dynamically

trim the craft and ensure pitch stability during operation. The limitation of such control surfaces is

that they are only effective for a range of less than 180 degrees.


Differential Thrust

Differential thrust may only be implemented in multiple propeller configurations and involves the

creation of a yawing moment through a differential in output between two sources. Differential thrust

is effective at driving yaw, however has the disadvantage that decreasing the thrust on one side

decreases the overall speed of the craft (Amyot, 1989). Additionally there is no mechanism to produce

a sidewards force, meaning this form of propulsion has inherent low maneuverability relative to other

thrust vectoring methods. (Amyot, 1989) Differential thrust is relatively simple to implement as no

complex mechanisms are required.

Direct Thrust Vectoring

Direct vecotoring of a thrust stream is the most effective method in terms of maneuverability as it

allows 360 degree rotation of the control vector. Direct thrust vectoring is complex to implement

relative to other methods as a complex mechanism is required to rotate the propeller assembly itself.

It maintains the high efficiency of air-screw propulsion systems, however, safety must be considered

due to the exposure of propeller blades. Additionaly, rotation of the propeller assembly demands

expensive spacial requirements. This method is effective as yawing moments can be created without

slowing the speed of the craft. Propellers may be completely reversed to provide backward thrusting

or braking of the platform.

The ability to statically hover was considered critical to the operational scenarios of the platform, and

therefore lift dominant methods were eliminated. Traditionally integrated propulsion methods do not

allow the hovercraft to remain stationary while in hover. This is because the propulsion fan must

be on to produce lift, and results in an accompanying thrust force. This incurred the elimination of

thrust dominant systems. Due to the application of the platform in mine detection it was necessary

to ensure the platform does not lower in operation. In order to achieve this, it was necessary to

ensure that pressure distribution in the air cushion remained constant. As such, air cushion integrated

methods such as puff ports were also eliminated. Control surface based control systems were considered

however were unable to provide the 360 degree of rotation required to provide the backward movement

and braking capability necessary to achieve the platforms operational behaviour. Another braking

mechanism was identified to integrate with control surface systems. The ability to drop or expand

the skirt at the front of the craft induces a drag at the front resulting in very effective braking. These

methods were disregarded due to high drag increasing the risk of mine detonation.

Based on these evaluations, Prototype 2 was selected. This configuration include


3.2.6 Prototype Specific Requirements

Prototype selection brought about a range of specific criteria used as limitations in detail design.

These requirements are summarised below:

The craft should be skirted to optimise efficiency

A plenum chamber configuration of the hull should be adopted.

The propulsion system should be vectored thrust and be capable of 360 degree vectoring, two

fans were selected so that smaller propellers could be used.

The lift system should idependently achieve the flow rates required to lift 100kg.

3.3 Power Requirements

Weight minimisation is a key feature of hovercraft design. While ideally the overall weight of a

hovercraft should be as low as is possible, in reality, there are only so many resources that should be

invested to this end. As such, sensitivity analysis is a valuable design tool that aids the designer when

comparing the selection of certain configurations and items. The following section considered two such

analyses, being the sensitivity of propulsion and lift requirements to the overall weight of platform.

3.3.1 Lift Power

The lift system must produce a steady state cushion pressure that will provide enough force to coun-

teract the weight of the craft, shown by equation 3.2

Pc = f(M, g) (3.2)

The sensity of lift requirements to weight were derived by differentiating the governing equations

(calculations detail in Appendix Q).This resultant graph is approximately linear, giving a sensitivity

of 29 W/kg for the lift system.

3.3.2 Propulsion Power

The power requirements for propulsion are dictated by the equation of drag, and thrust required to

overcome the inertia of the craft. The gross thrust is described by equation Q.5. Substituting in

3.3. POWER REQUIREMENTS 29

60 70 80 90 100

1.0

1.2

1.4

1.6

1.8

2.0

2.2

Power Lift System (kW)

Figure 3.6: Sensitivity of Lift Power to Mass

the equations for drag, equation Q.7 respresents the total thrust requirement. By differentiating this

equation we obtain the sensitivity of propulsion to weight.

TGross = TNET +DA +DC +DT +Df (3.3)

TGross = (ma) + (12V 2) +

QV

+ (mgsinT ) (3.4)

Figure Q.2 shows a calculated sensitivty of 7.8 W/N.

3.3.3 Preliminary Thrust and Power Estimates

As discussed is section 3.3.2, the gross thrust requirements can be calculated as a function of net forces

required to overcome drag. A Free Body Diagram (FBD) of the craft in Figure 3.8 shows the force

loading on the craft.

The drag forces associated with aerodynamics, the slope of the ground, and momentum of the cushion

air can be calculated using the standard equations in section 3.3.2. The preliminary calculations are

done respective to the design weight of 100kg. DA can be estimated using equation 3.5, giving a

value of 3.5N. This calculation is based on a light breeze of 2m/s acting against a wedge shape cross

sectional area. For this geometry Cd can be estimated at 0.5. (Munson et al., 2002)


4 0 5 0 6 0 7 0 8 0 9 0 1 0 001 02 03 04 05 06 07 08 09 01 0 0

Thrust

(N)

W e i g h t ( k g )

N o S l o p e 1 d e g 2 d e g 3 d e g 4 d e g 5 d e g

Figure 3.7: Sensitivity of Thrust to Weight and Terrain Slope

Figure 3.8: FBD of Forces

DA =12C

Final Report Compressed

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