UAV Plane Project

i

University Of Adelaide

School of Mechanical Engineering

2008

Honours Project 637:

Design and Build of a Pulsejet UAV

Ryan Anderson 1132309

Nicholas Lukacs 1133184

Mitchell OCallaghan 1131620

Karn Schumacher 1133398

Michael Sipols 1133364

Terry Walladge 1133113

iii

Sir Ross and Sir Keith Smith Fund Acknowledgement and

Disclaimer

Research undertaken for this report has been assisted with a grant from the Sir Ross

and Sir Keith Smith Fund (Smith Fund) (www.smithfund.org.au). The support is

acknowledged and greatly appreciated.

The Smith Fund by providing funding for this project does not verify the accuracy of

any findings or any representations contained in it. Any reliance on the findings in any

written report or information provided to you should be based solely on your own

assessment and conclusions.

The Smith fund does not accept any responsibility or liability from any person,

company or entity that may have relied on any written report or representations

contained in this report if that person, company or entity suffers any loss (financial or

otherwise) as a result.

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Executive Summary

The pulsejet powered Unmanned Aerial Vehicle (UAV) was designed and

manufactured by a group of six undergraduate engineering students from the School

of Mechanical Engineering at the University of Adelaide. The students, studying a mix

of mechanical and aerospace engineering, aimed to design and build a UAV powered

by a valveless pulsejet engine, which was also developed throughout the year. The use

of pulsejets in aviation history has been almost non-existent since the end of World

War II. However, interest in pulsejet technology has increased in recent years, as they

offer a cheap and viable alternative from turbojet and ducted fan engines. The design

of the aircraft was based around the pulsejet engine and is ultimately intended for use

as a high speed target drone or decoy aircraft.

The development of the valveless pulsejet engines followed of from work completed

by Coombes et al in 2007, with the aim to produce an engine and fuel system capable

for use in flight. A wide range of development was undertaken on three different

engines throughout the year, with over 100 static tests performed by the students.

Significant improvements were achieved in the areas of engine thrust, thrust specific

fuel consumption, engine weight and engine fuelling; most notably achieving

successful operation using liquid fuels.

The allowance for pulsejet engine installation meant that a conventional airframe

design was not suitable. A classical approach was taken to determine the performance

and stability of the airframe. This design incorporated low swept wings, dual vertical

stabilizers and an elevated swept tail, to produce an airframe that is capable of

pulsejet powered flight. The airframe was manufactured by the students under the

supervision and assistance of the Mechanical Engineering Workshop staff, and was

constructed primarily from composite materials.

Successful flight of the aircraft was achieved on a ducted fan as it was seen as a more

conventional power source, which has similar operational characteristics to the

vi

pulsejet engines. The flight tests showed that the airframe was stable, controllable and

maneuverable. A cruise speed of 150km/hr was achieved during a four minute flight.

The aircraft performed all handling requirements during the test flight.

The project goals set by the students at the beginning of the project reflected the

ambitious nature of the project. The extension goals were particularly ambitious and

related primarily towards the performance of the aircraft and engine. While some

goals were not completely achieved, most were well within the performance

capabilities of the aircraft.

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Acknowledgements

The group would like to acknowledge the many people who have helped make this

project possible. We would especially like to thank our supervisor Dr. Maziar

Arjomandi, whose guidance, support and technical knowledge has been invaluable in

ensuring the projects success.

The group would like to acknowledge the Sir Ross and Keith Smith Fund, whose

generous contribution was vital for the success of the project. Without the funds

passion for the development of Aerospace design and technology in South Australia,

the project would not be possible.

The group would also like to thank the School Of Mechanical Engineering, ASC and

Australian Aerospace for their generous contributions to the project.

The authors would also like to thank and acknowledge all of the individuals who have

spent countless hours with the group throughout the year. In particular, a special

thanks to Bill Finch, from the Mechanical Engineering Workshop, whose technical

knowledge and dedication were invaluable. The personal contribution of James Irvine,

from Irvine Aeropulse, for his in-kind sponsorship, guidance and assistance in the

development and operation of pulsejet engines was greatly appreciated. Finally, we

would like to thank John Modistach, for both his time and effort spent assisting us with

aircraft manufacture, as well as for passing on a wealth of knowledge, which assisted

us in the manufacture of the airframe.

ix

Disclaimer

This statement confirms that the work presented in entirely our own, unless

identified otherwise. The work presented was completed as part of the

requirements for the Degree of Bachelor of Engineering (Aerospace and

Mechanical respectively) at the University of Adelaide. This document describes

the work carried out by the students, as recorded in individual project

workbooks throughout 2008. The students acknowledge the penalties for

plagiarism, fabrication and unacknowledged syndication and declare that the

work presented is free of these.

Ryan Anderson Nicholas Lukacs

------------------------------------------- ----------------------------------------

Date: Date:

Mitchell OCallaghan Karn Schumacher

------------------------------------------- ----------------------------------------

Date: Date:

Michael Sipols Terry Walladge

------------------------------------------- ----------------------------------------

Date: Date:

xi

Contents

Sir Ross and Sir Keith Smith Fund Acknowledgement and Disclaimer ............................ iii

Executive Summary........................................................................................................... v

Acknowledgements .........................................................................................................vii

Disclaimer .........................................................................................................................ix

Contents............................................................................................................................xi

List of Figures .................................................................................................................xvii

List of Tables ................................................................................................................. xxiii

1 Introduction .............................................................................................................. 1

1.1 Project definition................................................................................................ 2

1.2 Project Aims ....................................................................................................... 2

1.2.1 Pulsejet Development................................................................................. 2

1.2.2 Airframe Development ............................................................................... 3

1.3 Project Goals ...................................................................................................... 3

1.4 Extension Goals .................................................................................................. 3

1.5 Scope .................................................................................................................. 4

2 Feasibility Study ........................................................................................................ 5

2.1 What is a Pulsejet............................................................................................... 5

2.2 Advantages + Disadvantages.............................................................................. 6

2.3 Pulsejet Engines in Aviation History................................................................... 7

2.4 Market Research and Benchmarking................................................................. 7

2.4.1 V-1............................................................................................................... 8

2.4.2 ENICS Drones .............................................................................................. 9

2.4.3 AMT Pulsejet Hobby Aircraft .................................................................... 10

2.4.4 Comparison to turbine engine UAVs or Target Drones............................ 10

2.5 Mission Profile Specifications .......................................................................... 11

2.5.1 Mission Profile .......................................................................................... 11

2.5.2 System Requirements............................................................................... 11

2.5.3 Takeoff methods....................................................................................... 14

2.5.4 Landing Options ........................................................................................ 15

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2.6 Power plant Design...........................................................................................15

2.6.1 Valveless Pulsejet - Thermodynamic Cycle ...............................................15

2.6.2 Review of Previous Work ..........................................................................17

2.6.3 Alternative Engine Designs........................................................................21

2.6.4 Exhaust Pipe Development .......................................................................24

2.6.5 Liquid Fuelling ...........................................................................................27

2.6.6 Thrust Augmentation ................................................................................29

2.7 Feasibility Study Summary................................................................................30

3 Conceptual Design...................................................................................................31

3.1 Aircraft Conceptual Design Introduction..........................................................31

3.2 Selecting Preliminary Aircraft Concept.............................................................31

3.2.1 General Configuration...............................................................................31

3.2.2 Fuselage Configuration..............................................................................32

3.2.3 Engine Configuration.................................................................................32

3.2.4 Wing Configuration ...................................................................................32

3.2.5 Empennage Configuration ........................................................................32

3.2.6 Landing Gear Configuration ......................................................................33

3.2.7 Basic Wing Parameters..............................................................................33

3.3 Developing concept for selected configuration ...............................................34

3.3.1 Concept Sketches ......................................................................................35

3.3.2 Statistical Calculations...............................................................................35

3.4 Designing technical parameters for concept....................................................38

3.4.1 Weight Estimation.....................................................................................38

3.4.2 Matching Diagram.....................................................................................39

3.4.3 Aerofoil Selection ......................................................................................42

3.5 Finalisation of Preliminary Aircraft Concept ....................................................45

3.5.1 Variation of Pulsejet Position in Concept Development...........................45

3.5.2 Empennage Design....................................................................................47

3.6 Finalization of Preliminary Aircraft Concept ....................................................52

3.6.1 Preliminary Conceptual Fuselage Design ..................................................52

3.7 Practical Modifications to Final Concept..........................................................53

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3.8 Engine Design ................................................................................................... 54

3.8.1 Exhaust Design Two Stroke Exhaust Similarities ................................... 54

3.8.2 Steady State Diffuser Design..................................................................... 57

3.9 FWE Bellmouth Development.......................................................................... 63

3.9.1 Starting Vortices........................................................................................ 63

3.9.2 Bellmouth Design...................................................................................... 64

3.9.3 Final Design............................................................................................... 67

3.9.4 Flight considerations................................................................................. 68

3.10 Flight Engine Development .......................................................................... 71

3.11 Liquid Fuel System Design ............................................................................ 76

3.11.1 Fuel Choice ............................................................................................ 77

3.12 Fuel Injector Design...................................................................................... 78

3.13 Conceptual Design Summary........................................................................ 83

4 Detailed Design ....................................................................................................... 85

4.1 Fuselage Structure Design................................................................................ 85

4.1.1 Fuselage Structural Layout ....................................................................... 85

4.1.2 Fuselage Structure Selection .................................................................... 88

4.2 Wing Design ..................................................................................................... 89

4.3 Wing Structural Design..................................................................................... 89

4.3.1 Lifting force profile.................................................................................... 89

4.3.2 Spar Design ............................................................................................... 95

4.3.3 Torsion ...................................................................................................... 97

4.4 Wing Connection............................................................................................ 101

4.5 Control Surface Sizing .................................................................................... 103

4.5.1 Aileron Sizing........................................................................................... 103

4.5.2 Elevator Sizing......................................................................................... 104

4.5.3 Servo Motor Sizing.................................................................................. 105

4.6 Pulsejet Engine Mount ................................................................................... 106

4.6.1 Mounting Locations ................................................................................ 106

4.6.2 Thermal Isolation .................................................................................... 107

4.6.3 Vibration Isolation .................................................................................. 108

4.6.4 Vibration Isolation Method: ................................................................... 110

xiv

4.6.5 Engine Mount Materials..........................................................................112

4.6.6 Final Design .............................................................................................113

4.6.7 Engine Modal Analysis.............................................................................117

4.7 Pulsejet Launch System ..................................................................................118

4.7.1 Launch process........................................................................................118

4.7.2 Launch Stand Components .....................................................................119

4.8 Electrical and Electronic Components............................................................121

4.8.1 Pump and related components...............................................................121

4.8.2 Radio Controller ......................................................................................122

4.9 Ducted Fan......................................................................................................123

4.9.1 Purpose of fan .........................................................................................123

4.9.2 Selection of fan system ...........................................................................123

4.9.3 Modifications to the airframe for Ducted Fan Testing ...........................127

4.10 Final Stability Analysis.................................................................................129

4.10.1 Longitudinal Moment Analysis ............................................................130

4.10.2 Roll Stability Analysis ...........................................................................134

4.10.3 Ground Performance...........................................................................135

5 Airframe Manufacture ..........................................................................................137

5.1 Available Manufacturing Methods.................................................................137

5.2 Wing Construction..........................................................................................138

5.3 Empennage Construction ...............................................................................140

5.4 Fuselage Construction ....................................................................................141

5.5 Internal Fuselage Construction ......................................................................144

5.6 Internal Access................................................................................................145

5.7 Propulsion System ..........................................................................................146

5.7.1 Ducted fan ...............................................................................................146

5.7.2 Pulsejet ....................................................................................................147

5.8 Landing Gears and Wheels .............................................................................148

5.9 Control System Installation ............................................................................149

6 Testing ...................................................................................................................151

6.1 Engine Testing.................................................................................................151

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6.1.1 Phase One Testing................................................................................... 152

6.1.2 Phase Two Testing .................................................................................. 155

6.1.3 Phase Three Testing................................................................................ 160

6.2 Aircraft Testing............................................................................................... 168

6.2.1 Wing Structural Testing .......................................................................... 168

6.2.2 Electrical Component Testing................................................................. 169

6.3 Aircraft Pre-flight Tests .................................................................................. 170

6.3.1 C.G. Test .................................................................................................. 170

6.3.2 Other pre-flight checks ........................................................................... 171

6.3.3 Location for flying ................................................................................... 172

6.3.4 Pilot ......................................................................................................... 173

6.3.5 Engine and Flight Tests ........................................................................... 173

6.4 Pulsejet Flight Test ......................................................................................... 179

6.5 Discussion of experimental results ................................................................ 180

7 Management......................................................................................................... 181

7.1 Time Management ......................................................................................... 182

7.2 Financial Management................................................................................... 184

7.3 Risk Management........................................................................................... 185

8 Conclusion and Future Work ................................................................................ 187

8.1 Review of project goals .................................................................................. 187

8.1.1 Extension Goals....................................................................................... 189

8.2 Project Concerns ............................................................................................ 190

8.3 Future Developments and Recommendations .............................................. 191

References .................................................................................................................... 195

Appendix A - Configuration Selection........................................................................... 199

Appendix B- Weight Calculation Method ..................................................................... 211

Appendix C Matching Diagram .................................................................................. 221

Drag polar estimation ........................................................................................... 221

Initial estimate of drag polar ................................................................................ 222

Climb requirements .............................................................................................. 223

Stall Requirement ................................................................................................. 223

Takeoff Field Length Requirement ....................................................................... 224

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Cruise Requirement...............................................................................................224

Adjusting to take-off values ..................................................................................225

Appendix D Sensitivity Analysis..................................................................................227

Appendix E Engine Mounting Calculations.................................................................233

Appendix F Liquid Fuels..............................................................................................235

Appendix G Component Weight Breakdown .............................................................239

Appendix H Test Log Books ........................................................................................241

Appendix I Fuselage Stress Analysis ...........................................................................279

Appendix J- Gantt Charts...............................................................................................281

Appendix K- Risk Register..............................................................................................285

Appendix L- Meeting Minutes.......................................................................................287

Appendix M- Drawings..................................................................................................367

xvii

List of Figures

Figure 1 - Valved and Valveless Pulsejet Designs ............................................................. 5

Figure 2 - Comparison of Engine Costs ............................................................................. 6

Figure 3-View of the V-1 ................................................................................................... 8

Figure 4-E-95 Ramp Launch .............................................................................................. 9

Figure 5- Flight Profile..................................................................................................... 11

Figure 6 - Statistical Trends of Target Drone UAVs ........................................................ 13

Figure 7 - Ideal Lenoir Cycle............................................................................................ 16

Figure 8-Pobezhimov modified Lenoir cycle................................................................... 17

Figure 9 - Valveless Pulsejet Engine (Carolina State University) .................................... 18

Figure 10 - Focus Wave Energy (FWE) Pulsejet Engine .................................................. 20

Figure 11-Chinese Valveless Pulsejet Engine.................................................................. 21

Figure 12-Lockwood Prototype ...................................................................................... 22

Figure 13-Escopette Valveless Engine ............................................................................ 23

Figure 14 - Interaction of Escopette Pressure Waves .................................................... 24

Figure 15 A Focused Wave (FWE) Pulsejet engine ...................................................... 25

Figure 16 A Lockwood-Hiller style Pulsejet engine,..................................................... 26

Figure 17 A Focused Wave engine variation, the FWE VIII - Lady Anne Boleyn. ..... 27

Figure 18- optimised thrust augmenter as used on a valved pulsejet ........................... 29

Figure 19-Configuration Concept Sketches .................................................................... 35

Figure 20: Statistical Thrust Loadings of Jet UAVs.......................................................... 36

Figure 21: Wing Loading Versus Weight of Jet UAVs ..................................................... 37

Figure 22: Statistical Concept ......................................................................................... 38

Figure 23: Matching Diagram......................................................................................... 40

Figure 24: Example of Early Design................................................................................. 46

Figure 25: Second Phase Design Example ...................................................................... 46

Figure 26: Final Engine Position...................................................................................... 47

Figure 27: Centre of Gravity Excursion Diagram............................................................. 49

Figure 28: Longitudinal X-Plot......................................................................................... 50

Figure 29: Lateral Stability X-Plot.................................................................................... 52

Figure 30 -Conceptual Fuselage Design.......................................................................... 53

xviii

Figure 31: Modifications to final aircraft concept...........................................................53

Figure 32- Advancements in Two Stroke Exhaust Design...............................................55

Figure 33 The effect of expansion angle on wave behaviour. .....................................56

Figure 34: Loss Coefficient for a Conical Diffuser ...........................................................58

Figure 35 The UFLOW1D model used to investigate expansion angles.......................59

Figure 36 Combustion chamber pressure extremes for different expansion angles. .60

Figure 37 - Statistical data showing exhaust expansion angles from similar engine

designs.............................................................................................................................61

Figure 38 - statistical data showing a trend between combustion chamber diameter

and expansion diameter..................................................................................................61

Figure 39 - The final expansion design............................................................................63

Figure 40 - PIV images of vortex interaction...................................................................64

Figure 41 - Bellmouth designs considered (Blair, Cahoon 2006) ....................................65

Figure 42 - Performance of bellmouth designs...............................................................65

Figure 43 - The data obtained in 2007 using UFLOW1D (blue) and textbook

recommendations (red) ..................................................................................................66

Figure 44 - The adjustable bellmouth design..................................................................68

Figure 45- Three intake geometries ................................................................................69

Figure 46- Domain Layout ...............................................................................................69

Figure 47- Effect of intake geometry on mass flow rate.................................................70

Figure 48 -Static Pressure Contours of Aerodynamic Flare at 80m/s.............................70

Figure 49-Static Pressure Contours on Standard Flare at 80m/s....................................71

Figure 50- Statistical trend of Chinese and FWE engines ...............................................72

Figure 51-Variation of material properties of 310 stainless steel with temperature.....73

Figure 52-Operating pressure of the Escopette pulsejet................................................74

Figure 53- full engine mesh.............................................................................................75

Figure 54-pressure loading input for flexible dynamic solver.........................................75

Figure 55-Stress Results on Combustion Chamber End Cap...........................................76

Figure 56- Final Results of the Axi Symmetric Model .....................................................76

Figure 57- 12 hole swirl injector......................................................................................79

Figure 58- 6 hole opposed spray injector........................................................................79

xix

Figure 59-BETE PJ Cone Spray Injector ........................................................................... 80

Figure 60-5mm stainless steel injectors ......................................................................... 81

Figure 61: Conceptual Design Three View...................................................................... 83

Figure 62: Overview of Fuselage Structural Layout....................................................... 85

Figure 63: Fuselage Internal Reinforcing Structure ........................................................ 86

Figure 64 - Schrenk's Approximation.............................................................................. 90

Figure 65 -Lifting Force Distribution ............................................................................... 91

Figure 66- wing shear distribution.................................................................................. 92

Figure 67 - wing bending force distribution ................................................................... 92

Figure 68 - Corrected Cl Distribution .............................................................................. 93

Figure 69 - Lift Distribution at 88m/s.............................................................................. 94

Figure 70 - Maximum spar thickness from root to tip of the wing ................................ 96

Figure 71 - Position of Centre of Pressure with AOA...................................................... 98

Figure 72 - Wing Torque at Takeoff (70km/hr)............................................................... 99

Figure 73 - Wing Torque at Climb Speed (150km/hr)..................................................... 99

Figure 74 - Wing Torque at Cruise Speed (300km/hr).................................................. 100

Figure 75- Wing Connection System............................................................................. 101

Figure 77 - The mounting extension on the front of the Chinese engine .................... 107

Figure 78 - Force transmissibility as a function of frequency ratio and damping ratio109

Figure 79 - Yield stress relative to room temperature as a function of temperature for

301,302,304,321,347 annealed stainless steels ........................................................... 113

Figure 80 - The final engine mount design. The modification made to the front of the

engine is shown in green. ............................................................................................. 114

Figure 81 - Thermal analysis results of the engine mount. .......................................... 114

Figure 82 - Stress distribution within the initial design under an 80N load................. 115

Figure 83 - Stress distribution within the design under dynamic loading of 40N +- 20N

...................................................................................................................................... 116

Figure 84 - 208Hz vibration mode of the engine, mounted at ends ............................ 117

Figure 85 - Release tab attached to the intake of the engine, and release tab on the

launch stand.................................................................................................................. 119

Figure 86 - Launch stand for pulsejet flight .................................................................. 120

Figure 87: Flight Works Fuel Pump .............................................................................. 121

xx

Figure 88 - Schubeler Ducted Fan .................................................................................123

Figure 89 - Lehner electric motors ................................................................................125

Figure 90 - ZIPPY-R battery pack ...................................................................................126

Figure 91 - Ducted fan mounted in the airframe..........................................................127

Figure 92 - Ducted Fan Mounting Tabs .........................................................................128

Figure 93 - The cover design for the ducted fan ...........................................................129

Figure 94 - The cover installed on the plane.................................................................129

Figure 95: Centre of Gravity and Aerodynamic Centre Excursion Diagram..................131

Figure 96:Cm-Cl Graph (Power On)...............................................................................132

Figure 97: Cm-Cl Graph (Power On)..............................................................................132

Figure 98: Cm-Cl Graph (Pulsejet) .................................................................................133

Figure 99: Roll Stability Contributions...........................................................................135

Figure 100 - Rib Installation in Wings............................................................................139

Figure 101 - Wing structure schematic .........................................................................140

Figure 102 - Servo Installation.......................................................................................140

Figure 103 - a) Horizontal tail joined as a single piece, b) horizontatal tail after glassing,

c) installation of vertical tail onto fuselage...................................................................141

Figure 104 - Fuselage plug.............................................................................................142

Figure 105 - Gel coat being applied to plugs in preparation for creating the moulds..143

Figure 106 - Fuselage.....................................................................................................144

Figure 107 - Location of bulkheads (blue) and longerons (red)....................................145

Figure 108 - The aircraft showing the both access panels a) removed and b) attached

.......................................................................................................................................146

Figure 109 Schubeler ducted fan (Schubeler Jets, 2008)...........................................147

Figure 110 - Front pulsejet engine mount ....................................................................148

Figure 111 - Front landing gear steering system...........................................................149

Figure 112 - Test System Layout ...................................................................................151

Figure 113 Reducing thrust during extended operation............................................153

Figure 114 Effect of fuel injection position on engine performance .........................153

Figure 115 Effect of exhaust and intake length on engine performance ..................154

xxi

Figure 116 - The adjustable FWE engine with expanding tail section and 100mm

extension....................................................................................................................... 156

Figure 117 - Affect of injector position on engine thrust ............................................. 157

Figure 118 - Thrust Results ........................................................................................... 158

Figure 119 - Visible damage to ceramic coating........................................................... 159

Figure 120 - liquid fuel injectors placed mid way along the intake tube ..................... 161

Figure 121 - Opposed injector configuration................................................................ 163

Figure 122 - Performance of the Chinese engine with different injector placements. 163

Figure 123 - engine performance on various fuels....................................................... 164

Figure 124 - Performance of the Chinese engine for various lengths.......................... 166

Figure 125 - Aircraft testing flow chart......................................................................... 168

Figure 126 Load zones for wing structural testing .................................................... 168

Figure 127 - Experimental Wing Deflection.................................................................. 169

Figure 128 - C.G. Test Setup.......................................................................................... 170

Figure 129 - C.G. Test Photo ......................................................................................... 171

Figure 130 - Ground Roll Test at Gawler Airfield.......................................................... 174

Figure 131 - Plotted flight path from GPS logger.......................................................... 176

Figure 132-Compact Gantt Chart.................................................................................. 183

Figure 133-Cost Breakdown.......................................................................................... 185

Figure 134: Mock graphic of selected configuration ................................................... 209

Figure 135- Graph of WE/WO Vs WO........................................................................... 212

Figure 136- Graph of WE/WO Vs WO........................................................................... 217

Figure 137- Graph of WE/WO Vs WO for Consistent Data........................................... 219

Figure 138: First Estimate of Drag Polar ...................................................................... 222

Figure 139: Sensitivity to fuel consumption ................................................................ 227

Figure 140: Sensitivity to Engine Weight ..................................................................... 228

Figure 141: Sensitivity of Cruise Speed to W/S ............................................................ 228

Figure 142: Sensitivity of Takeoff Distance to W/S ...................................................... 229

Figure 143: Sensitivity of Climb Rate to W/S................................................................ 229

Figure 144 : Sensitivity of Stall Speed to W/S............................................................... 230

Figure 145: Sensitivity of Cruise Speed to T/W ............................................................ 230

Figure 146 : Sensitivity of Takeoff Distance to T/W ..................................................... 231

xxii

Figure 147 : Sensitivity of Climb Rate to T/W ...............................................................231

Figure 148- Engine during Test......................................................................................245

Figure 149- Thrust Vs Time for Test 6 ...........................................................................247




Figure 153- Thrust Vs Time for Test 10 .........................................................................250




Figure 157- Thrust Vs Time with injector 32mm from intake mouth ...........................259

Figure 158- Time Vs Thrust for FWE with expanding Exhaust ......................................268

Figure 159 - Engine performance on liquid fuels ..........................................................278

xxiii

List of Tables

Table 1- Specifications of the V-1 ..................................................................................... 8

Table 2- Specifications of ENICS E95 Target Decoy .......................................................... 9

Table 3- Specifications of AMT Pulsejet aircraft............................................................. 10

Table 4- Lockwood Performance Data ........................................................................... 23

Table 5 : Requirements and Input Data of Matching Diagram....................................... 40

Table 6 Characteristics of Suitable Aircraft.................................................................. 41

Table 7: Characteristics of Possible Aircraft ................................................................... 41

Table 8- Initial Aerofoil Analysis ..................................................................................... 43

Table 9: NACA 4 Digit Aerofoil Analysis .......................................................................... 43

Table 10- Suitable Tail Aerofoils ..................................................................................... 44

Table 11........................................................................................................................... 82

Table 12: Fuselage Stress Analysis Results ..................................................................... 88

Table 13 - Aileron Dimensions ...................................................................................... 104

Table 14- Servo Requirements...................................................................................... 105

Table 15 - Spring stiffness and deflection under a 40N thrust load, for various frequecy

ratios. ............................................................................................................................ 110

Table 16: Material Selection for Engine Mount............................................................ 112

Table 17 - Ducted Fan Parameters ............................................................................... 124

Table 18 - Parameters of Lehner 1950 Electric Motor ................................................. 125

Table 19 - Expanding Exhaust Test Results................................................................... 156

Table 20 - Maximum control surface/servo motor deflection..................................... 170

Table 21 - Flight data from GPS logger ......................................................................... 176

Table 22- Hours Worked By Group Members .............................................................. 184

Table 23: General Configuration Decision Matrix ........................................................ 201

Table 24: Fuselage Configuration Decision Matrix ....................................................... 202

Table 25: Engine Configuration Decision Matrix .......................................................... 203

Table 26: Wing Configuration Decision Matrix............................................................. 204

Table 27: Wing Height Decision Matrix ........................................................................ 205

Table 28: Wing Sweep Decision Matrix ........................................................................ 206

Table 29: Empennage Configuration Decision Matrix .................................................. 207

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Table 30: Landing Gear Type Decision Matrix...............................................................208

Table 31: Landing Gear Arrangement Decision Matrix.................................................208

Table 32- Weight Data for Piston UAVs ........................................................................211

Table 33- Table of First Iterations .................................................................................216

Table 34- UAV Data .......................................................................................................216

Table 35- Consistent UAV Weight Data ........................................................................218

Table 36- Iteration Results ............................................................................................220

Table 37- Fuel Flash Point Data.....................................................................................235

Table 38: Fuel Energy Density Data...............................................................................236

Table 39: Fuel Optimal AFR Data...................................................................................236

Table 40- Fuel Flammability Limit Data.........................................................................237

Table 41- Latent Heat of Vaporisation Data..................................................................238

Table 42 : Component Weight Breakdown...................................................................239

1

1 Introduction

The purpose of this project was to design and manufacture a Valveless Pulsejet

Powered Unmanned Aerial Vehicle (UAV), suitable for use as a Target Drone or Decoy

UAV. The project aimed to develop an understanding of valveless pulsejet engines, as

well as developing a prototype engine, with the aim of showing that they are a cheap

and viable alternative form of propulsion.

A feasibility study was initially conducted in order to develop project goals and define a

realistic scope. This stage included an extensive study of all valveless pulsejet engines,

developed by academics and enthusiasts, in order understand the working

characteristics of the engines, and to better understand how to optimise and improve

the operating characteristics of these engines. A study of target drones and decoy

aircraft, powered by both pulsejet and turbo jet engines was undertaken to help

develop the fundamentals of the aircraft, as well as to identify some of the key issues

which needed to be addressed in the following design stages.

The engine design was initially a continuation and modification of a Focused Wave

Energy (FWE) valveless pulsejet engine developed by Coombes et al in 2007 at the

University of Adelaide.

The aircraft design was produced initially using a combination of statistical and

numerical analysis, in consultation with aircraft design literature. The aircraft design

was then progressively refined in an iterative manner.

This project has involved a significant testing section, with over 100 static engine tests,

conducted, and two successful aircraft flights. The data obtained from this project has

helped to better develop the understandings of valveless pulsejet operational

characteristics, particularly with liquid fuels.

This report shows the development steps which were utilised to ensure the project

was completed on time; on budget and that all goals were achieved. This project has

Chapter 1 Introduction

2

shown through proof of concept that valveless pulsejet engines are a viable form of

propulsion for short range target drones and decoy UAVs.

1.1 Project definition

The project continues on from the work conducted by Coombes et.al in 2007. This

project expands from that work to concern the development of a valveless pulsejet

powered UAV.

The preceding data and research from the detailed feasibility study and bench-marking

has been synthesised to produce this project definition, which outlines the aims and

objectives of the project. This project definition is categorised into the Pulsejet and

Airframe development areas.

1.2 Project Aims

The project aims to show that valveless pulsejets are a viable alternative engine for

short range and low cost UAV aircraft. To ensure the project is completed the

following must be achieved.

1.2.1 Pulsejet Development

Continued development of a valveless pulsejet, with the aim of increasing the

overall thrust of the engine and a reduction in engine weight based on 2007

results.

Research and development of a liquid fuel delivery system for pulsejet engines.

Develop a fuel system that is of suitably low weight for flight.

Successfully test and record key performance criteria of the pulsejet on both

gas and liquid fuel mixes.

Development of alternative engine designs which may be suitable for future

development.

Completion of all tasks within the allocated budget.

Section 1.3 Project Goals

3

1.2.2 Airframe Development

Successful design of a low weight air-frame, based on the parameters of an

estimated 3kg of thrust and of plausible 300km/hr max speed.

Successful manufacture of the airframe using composite materials within the

specified weight.

Successful flight of the UAV.

Completion of all tasks within the allocated budget.

1.3 Project Goals

The project success was based on the completion of the following goals:

To modify, build and manufacture a valveless pulsejet, with the aim of

producing 3kg of thrust, with an engine weight of 1.5kg or less. This goal will be

quantified by the output received from the thrust measurement stand

constructed during the 2007 Project.

Develop a liquid fuelled system for a pulsejet engine and integrate a flight

weight version into the UAV design.

Based on the desired pulsejet specifications; design, develop and build a

lightweight UAV capable of sustaining flight for 10 minutes with thrust supplied

by a valveless pulsejet engine.

Achieve a cruise speed of over 200km/h. As measured by onboard GPS or a

similar system.

Achieve a flight time of 10 minutes

Gain a better engineering perspective on the workings of pulsejets, with the

aim of developing different engine design alternatives.

1.4 Extension Goals

Completion of extension goals will show above expected outcomes from the project:

Achieve 3.5kg of thrust from a valveless pulsejet engine.

Chapter 1 Introduction

4

Achieve a cruise speed of 250 km/h or above.

Increase flight time of the proposed liquid fuelled pulsejet UAV to over 15

minutes.

Manufacture an alternative engine design for future development.

1.5 Scope

The project scope is limited to the successful completion of the goals specified above.

The project aimed to design an airframe capable of supporting a pulsejet engine. While

this involved some optimisation of the airframe structure, the project only intended to

develop a proof of concept aircraft. The project is aimed to develop an aircraft capable

of flight, the scope of the project is limited to the initial development and

manufacturing stages, further alteration and optimisation after successful flight was

minimal.

The engine and fuel delivery systems were designed to be capable of producing 3kg of

static thrust for an estimated 10 minute flight time. The scope of this project was

therefore limited to the development of these systems to a level which will allow the

aircraft to sustain flight for the desired time period. Continued development of the

systems to optimise flight of the aircraft is not anticipated unless project goals are not

fulfilled.

5

2 Feasibility Study

The aim of this feasibility study was to construct realistic project goals, understand the

challenges and risks involved with the project and formulate a logical and progressive

development plan for the remainder of the project. This was completed through a

literature review and market survey of both the airframe and pulsejet components of

the project.

2.1 What is a Pulsejet

A pulsejet engine is a form of combustion engine with few to no moving parts. The

engine comes in two forms, valved or valveless (Figure 1). Both engines have similar

layouts, consisting of an intake, combustion chamber and exhaust.

Figure 1 - Valved and Valveless Pulsejet Designs

(Pulse-jet.com 2008)

The main difference between the two engines is in the use of a valve to direct the flow

out of the exhaust tube. This valve was the main source of problems in early pulsejets.

As can be seen in Figure 1, the valve in the valved engine is positioned inside the

combustion chamber. The combination of extreme heat and violent closing movement

of the valve meant that valved pulsejets often experienced lifetimes only lasting

several minutes before the vales fatigued.

Chapter 2 Feasibility Study

6

The valveless pulsejet uses an aerodynamic valve, created by the differences in length

between the intake and exhaust, in order to sustain operation. This means the engine

has no internal parts, and thus is significantly more reliable once and effective engine

layout has been created. It is for this reason that valveless pulsejet engines have been

investigated in this project.

2.2 Advantages + Disadvantages

The main advantage of valveless pulsejet engines is in their extreme low cost, as

shown in Figure 2. This is due to the engines simple design, and use of low cost and

readily available materials and manufacturing methods. This makes them an excellent

power plant for low cost target drones and decoy UAV (Tao 2006).

Figure 2 - Comparison of Engine Costs

Pulsejet engines however suffer mostly from their poor thermodynamic efficiency

(outlined in section 2.6.1), which means the specific fuel consumption of the engines is

significantly greater than that of common turbojet or turbofan aircraft.

The other disadvantage of pulsejet engines is the extreme levels of noise and vibration

they emit. This factor rules out the use of pulsejets in anything other than military

applications.

However the most interesting and exciting area of pulsejet engines is in the

combustion mechanism. Pulsating combustion is self compressing, so that the air fuel

Section 2.3 Pulsejet Engines in Aviation History

7

mixture does not burn steadily, but in bursts. This makes pulsejet engines an excellent

research engine, as many of the fundamental theories have been investigated on

pulsejets, before the construction of a large scale Pulse Detonation Engines (Wilson,

Dougherty 2002).

2.3 Pulsejet Engines in Aviation History

The pulsejet engine first found application in aircraft in 1891. Pulsejet engines have

been used throughout aviation history in several applications, including unmanned

military vehicles, early missile development, and vertical takeoff and landing (VTOL)

research, however much of the recent research has been undertaken by model aircraft

enthusiasts.

Sometime after the invention of the Pulsejet the Pulsejet powered German V-1 Missile

was produced. This missile is the pulsejet powered aerial vehicle produced in the

largest quantities with approximately 30,000 units manufactured. The V-1 missile

utilised a valved pulsejet engine and during tests of the V-1 significant failures

occurred, even though the aircraft only flew for less than 20 minutes (Goeble 2003).

In modern times much development in pulsejet engines has come from model aircraft

hobbyists, due to its low cost and comparable ease of manufacture.

The Pulsejet Engine has been of interest to commercial manufacturers throughout

several brief periods in history. Pulsejets have been used commercially and for the

military as propulsion devices for target drones.

2.4 Market Research and Benchmarking

The aim of this section was to gain an understanding into the capabilities and aircraft

configuration styles of pulsejet powered aircraft. Due to the lack of such aircraft, the

study was extended to both hobby aircraft and jet powered target drones and decoy

aircracft.


8

2.4.1 V-1

The V-1 was the first pulsejet powered aircraft, used by the German Air force during

World War II as a low cost and high quantity missile. It was the first mass-produced

guided missile and first jet powered aircraft.

Specifications of the V-1 can be seen in Table 1. The design of the V-1 is shown in

Figure 3.

Figure 3-View of the V-1

(Naughton 2001)

Table 1- Specifications of the V-1

(Combined from: Werrel 1985, Goebel 2003, Naughton 2001)

Engine Argus valved pulsejet 109-014

Thrust (kg) 272

Take-off weight (kg) 2150

Speed (kph) 630

Span (m) 5.3

While the size and weight of the aircraft is significantly larger than the anticipated UAV

weight, it useful for analysis as it is one of few aircraft which has been powered by a

pulsejet engine.

Section 2.4 Market Research and Benchmarking

9

2.4.2 ENICS Drones

ENICS is a Russian company which provides pulsejet powered decoy aircraft for

military training. ENICS produces fully manufactured drones and engines in three

different configurations. Full details of their E95 target decoy can be seen in Table 2.

Table 2- Specifications of ENICS E95 Target Decoy

(Enics 2006a)

Engine Enics M44D pulsejet

900 mm length, 75mm diameter

Engine weight (kg) 0.9

Thrust (kg) 20

SFC (kg/kg/hr) 6.61

Take-off weight (kg) 70

Span (m) 2.4

Speed (kph) 400

Range (km) 70

Endurance (min) 30

Launch Ramp, pneumatic

Figure 4-E-95 Ramp Launch

(Enics 2006b)

The aircraft is larger than the estimated project design, however its use as a target

drone and use of a valveless pulsejet engine make it an excellent aircraft for analysis.


10

2.4.3 AMT Pulsejet Hobby Aircraft

Pulsejets are moderately popular as propulsion systems for jet model aircraft. Pulsejets

are attractive to many pilots as they are low cost and offer good thrust to weight

ratios. In most cases commercially available valved engines are used.

This AMT Pulsejet is a custom built delta wing aircraft with a modified valved pulsejet

producing 8.7kg of thrust. The specifications of this aircraft can be seen in Table 3. This

aircraft is useful for analysis as it is close to the expected weight of the aircraft and its

use of a pulsejet allows analysis of expected fuel consumption during flight.

Table 3- Specifications of AMT Pulsejet aircraft

(AMT 1998)

Engine Custom valved pulsejet

Engine length (mm) 880

Engine diameter (mm) 90

Thrust (kg) 8.7

Take-off weight (kg) 7.5

Empty weight (kg) 5.9

Speed (kph) 390

Span (m) 1.12

Fuel Consumption 500 mL/min

[50% Kerosene, 40% Gasoline, 10% Propylene

Oxide]

2.4.4 Comparison to turbine engine UAVs or Target Drones

Turbine engines UAVs similar in size to the project aircraft have a large advantage in

terms of thrust to weight comparison to pulsejet engines. This is due to the

compactness of the engines, as well as comparably lower fuel consumption figures.

However the main disadvantage of these types of engines is the cost of the engine for

the similar amount of thrust, as shown in Section 2.2. For the statistical design of the

aircraft, turbine powered UAVs will be included in the analysis, due to the low number

of pulsejet powered aircraft, specifically of comparable size to the anticipated design

size of the aircraft.

Section 2.5 Mission Profile Specifications

11

2.5 Mission Profile Specifications

2.5.1 Mission Profile

Based on the analysis of the aircraft in Section 2.4 , the mission profile of the aircraft

was developed. As the aircraft was aimed to be developed as a proof of concept

aircraft, it was decided that the mission profile would be kept simple. The profile can

be seen in Figure 5.

Figure 5- Flight Profile

Further details are specified for some sections of this profile:

Start up and warm up - with pulsejets this is especially critical, as the engines

must be stable before launch. As a result, the fuel consumption during this

period will be significantly higher than for other engine types.

Loiter The goal of the flight is top remain airborne for 10-15 minutes with no

set range goal therefore the flight will take place within the line of sight of the

pilot.

2.5.2 System Requirements

The system requirements define the abilities of the aircraft and its components. These

values are determined from know requirements, calculations and the market research

performed on similar aircraft.


12

Cruise Speed Requirements

In section 2.4, different aircraft that utilized pulsejet engines or jet engines for power

were analysed. A suitable requirement for the cruise speed can be decided based on

that data and other calculations. A realistic cruise speed requirement was determined

based on numerous things.

Direct Bench Marking

The direct bench marking here refers to other pulsejet aircraft of similar size. A small

pulsejet aircraft presented earlier that was similar was the AMT. This had a top speed

of 390 kph, but also had a thrust to weight ratio greater than what we are aiming for.

Collated statistics of other Jet UAVs

Of the aircraft identified in the research and benchmarking section it can be seen that

most jet powered target drone aircraft have a cruise speed of approximately

400km/hr. However these aircraft have high thrust loadings and also high wing

loadings which reduce wing area and thus drag/weight. These characteristics are

allowed by the use of rocket-assisted launch and/or ramp launches and multiple or

more powerful engines. The following graph shows the thrust loading for a variety of

aircraft. It can be seen that the mean thrust loading is approximately 0.3. This was the

basis for all further aircraft development.

Section 2.5 Mission Profile Specifications

13

Figure 6 - Statistical Trends of Target Drone UAVs

Estimated available thrust

The amount of thrust currently available from the engine that is to be used for this

aircraft is 2.3kg (Coombes et.al 2007). This is described in more detail in Section 2.6.2

Estimated possible speed

Using calculations that estimate the drag based on the estimated drag in conjunction

with thrust and weight, it was possible to estimate the possible top. For thrust around

2.3 kg, and with a thrust loading of 0.3, from the mean of the collated data, top speeds

of 200-250 kph are possible.

Plausible Cruise Speed Requirement

Based on the above considerations, a realistic cruise speed requirement was deemed

to be 200 kph.

Control and Electronic Requirements

There were two separate control functions for the aircraft, control of the flight and

control of the engine.

Control of Flight


14

In selecting a control mechanism for the flight of the UAV it was determined that

simplicity was of importance, due to this a common remote controlled system was

deemed appropriate over other systems.

Control of the Engine

The thrust produced by the engine could be controlled by varying the fuel flow rate

supplied to the engine by the fuel pump.

2.5.3 Takeoff methods

There are numerous ways that a UAV system can be launched including trolley

launched and fixed gear. These methods have significantly different characteristics and

will be discussed.

Trolley Launched

The idea of a UAV being launched from a trolley or with a detachable landing gear is

that once the aircraft leaves the ground the trolley or gears detach from the aircraft.

This can be done using the propulsive power of the aircrafts own propulsion system

and or with a supplementary propulsion system such as rockets or sling shot. This take-

off method requires that the aircraft has an alternate landing method other than via

landing gear. The advantage of this launch method is that it has no need for a landing

gear which would decrease drag during flight. However the main disadvantage is that

it requires an alternate landing method such as a parachute.

Fixed Gear

For an aircraft taking off from an attached landing gear both fixed and retractable

types of landing gear designs can be considered. The main advantage of a fixed gear is

that the system is reliable and simple however it has a disadvantage of increased drag

during flight.

Section 2.6 Power plant Design

15

2.5.4 Landing Options

There are several alternative landing methods for UAVs without a conventional landing

system. These options have been considered to determine the overall risk and

feasibility of designing an aircraft without a conventional style landing gear. The four

options considered are parachute, belly landing, net catch and air cushioned landing.

Parachute

There are numerous advantages to landing an aircraft with a parachute. Recovery

parachutes are commercially available at a relatively low cost and they produce

minimal extra drag in comparison to a fixed landing gear system. The main

disadvantages of a parachute recovery are the complexity and weight of the system

and the high loads experienced when the parachute is first deployed.

Belly Landing

The use of a belly landing for an aircraft has numerous benefits, primarily the minimal

effect on drag, the slight effect on the weight of the aircraft and the low complexity of

the system. For a belly landing the underside of the aircraft is reinforced to withstand

the forces created by the impact of the aircraft with the ground, which is the main

disadvantage of this system.

2.6 Power plant Design

The power plant for the engine was defined by the initial project outline. This section

outlines the initial research that was conducted by the group into the workings,

research and challenges that exist in designing a valveless pulsejet engine.

2.6.1 Valveless Pulsejet - Thermodynamic Cycle

Pulsating combustion is the main area of confusion for researchers attempting to

successfully understand the operation of pulsejet engines. In the research conducted,

it has been noticed that different authors associated the behaviour of the engines to


16

different phenomenon. The self sustaining, periodical nature of the combustion is

generally associated with either wavy, acoustic or vortex nature (Pobezhimov 2006),

however models using these analysis generally can only describe parts of the

combustion process accurately. A thermodynamic approach can be used to explain the

operating process of a pulsejet engine, and show the advantages that exist in pulsating

combustion. The operating cycle of a pulsejet engine can be described by

modifications to the Lenoir Cycle which can be seen in Figure 7.

Figure 7 - Ideal Lenoir Cycle

(Pobezhimov 2006)

The operating cycle is described in thee steps:

1-2 Constant volume (isochoric) heat addition

2-3 isentropic expansion.

3-1 Constant pressure (isobaric) heat rejection - compression to the volume

at the start of the cycle.

The main difference between the Lenoir cycle and a pulsejet cycle is that during heat

addition the process is neither isochoric or isobaric, as there is a combination of

pressure release, and heat release (McCalley 2006). This is because the engine

operates from wave compression which is relatively weak; therefore combustion is not

confined to the combustion chamber, but occurs down the length of the engine. A

more realistic diagram can be seen in Figure 8.


17

Figure 8-Pobezhimov modified Lenoir cycle

(Pobezhimov 2006)

2.6.2 Review of Previous Work

From the research conducted, it was found that the development of pulsejet engines

has been the recent study of several universities. The two of interest to this project

were studies conducted by North Carolina State University and The University of

Adelaide. The work conducted by these two bodies allowed for a better understanding

on the fundamentals of pulsejet engine operation and optimisation.

North Carolina State University

Within the past decade, numerous investigations have been conducted by North

Carolina State University Masters students, under the direction of Dr. William L.

Roberts into various areas of pulsejet engine development. Studies have included:

Experimental Investigations into Pulsejet Engines

Experimental Investigations Into The Operational Parameters of a 50

Centimetre Class Pulsejet Engine

Experimental Investigations in 15 Centimetre Class Pulsejet Engines

Experimental Investigations of 8 Centimetre Class Pulsejet Engines

Experimental Investigations of Liquid Fuelled Pulsejet Engines

Numerical Simulations of Pulsejet Engines


18

These investigations have aimed to better understand the operating characteristics of

valved and valveless pulsejet engines, as well as attempting to develop small scale

engines for use with small size UAV and MAV aircraft, as the efficiency of commonly

used turbojets becomes lower as the size of the engine decreases (Tao 2006).

This section covers some of the key research conducted by these projects, with focus

on fundamental operating theories and engine performance. Work into the

development of liquid fuelled pulsejet engines, as conducted by McCalley in 2006, is

covered in section 27.

Valveless Engine Studies

Valveless engines studies conducted at Carolina State University have revolved around

the analysis of straight exhaust valveless engines, known as Schubert jets, (Figure 9),

with varying lengths and diameters of the intake and exhaust pipes. Schubert jets are

known for their ease of manufacture, but low thrust and high specific fuel

consumption.

Figure 9 - Valveless Pulsejet Engine (Carolina State University)

Experimental data was taken from the engines via a number of different mechanisms,

including instantaneous pressure sensors, manometers, thermocouples and SPL

meters.


19

Experiments in varying the length of the valveless pulsejet engine showed a direct

correlation between operating frequency and length. This frequency can be linked

directly to the Helmholtz frequency for the intake pipe (Equation 1) and a 1/4 wave

tube frequency for the exhaust (Equation 2).

Equation 1

Equation 2

LCf4

=

It was found that both these frequencies act together to give the engine operating

characteristics which are similar to that of a 1/6 wave tube. This was compared to

tested data and was found to be accurate to within 5%. The equation is temperature

dependant, which suggests that changes in area in the engine can cause a change in

the operation frequency. Also, changes in fuel will alter the burn temperature and thus

affect the engines operating characteristics. However it was found that if the intake

and exhaust frequency are within 10% of each other, the engine will successfully

operate.

Studies by Ordon in 2006 showed that this frequency characteristic is altered

significantly by changes in geometry, as these cause reflections in the waves, which

effect how the jet operates. It was found later by Kiker that the operating frequency of

the pulsejet scales as the inverse of the inlet length and reducing the exhaust diameter

of the pulsejet has very little effect on its operating frequency. With respect to

combustion chamber pressures, Kiker found that pressure scaled inversely with exit

diameter and directly to fuel flow rates. He also investigated the use of platinum

coating in a 5cm pulsejet to act as a catalyst and increase chemical reaction time.


20

2007 Study University of Adelaide

In 2007, a study by Coombes et.al Al 2007, was conducted at Adelaide University into

the devolvement and testing of a valveless pulsejet engine and thrust measurement

stand. The work aimed to create an engine capable of 3kg of thrust, with an engine

weight of under 2kg, a stand capable of accurately measuring the engines thrust during

tests and a software package to be used to predict pulsejet performance and allow the

optimization of engines

The groups work focused on the development of a Focus Wave Energy (FWE) Valveless

pulsejet engine, as shown in Figure 10, which was originally developed by notable

pulsejet engine developer, Larry Contril.

Figure 10 - Focus Wave Energy (FWE) Pulsejet Engine

Two engines were developed, the first based on statistical design, with adjustable

lengths. This engine aimed to investigate the effect of the intake and exhaust lengths

on engine performance, and a fixed length engine, developed based on findings from

the engine prediction program.

The work completed produced an optimum engine configuration which produced

2.392kg of static thrust with a total length of 1035mm. The second engine developed

was not successful in achieving sustained combustion.


21

The notable areas of interest are in the relationships which lead to the design of their

statistical based engine, the testing procedure they utilized, the theory behind the

development of the engine design software, and finally the problems and risks they

encountered throughout the project.

2.6.3 Alternative Engine Designs

Numerous different valveless engine designs have been developed, with the aim of

improving the performance of the engines. In selecting a valveless engine for use on a

UAV, thrust output, fuel consumption and aerodynamic performance must be

considered. This section outlines some of the most successful pulsejet engines which

have been developed, with the aim of identifying the most suitable engine for a flight

weight aircraft.

Chinese Pulsejet Engine

The Chinese Pulsejet engine was developed in the 1960s by CS manufacturing, a 2-

stroke motor designer from Shanghai. The engine is characterised by its expanding tail

exhaust and cylindrical combustion chamber (Figure 11). CS manufactured two

commercially available engines, which were designed to run on regular gasoline. In

1993 the designs for the engine became public, and it has since been developed by

enthusiasts for use with propane fuel systems.

Figure 11-Chinese Valveless Pulsejet Engine

(Beck 2008)


22

The engine is streamline in design, with rearward facing exhaust and intake to ensure

all thrust created acts in the same direction. No analytical research has been

conducted into this specific design, however specific fuel consumptions of between

3kg/kg/hr and 6kg/kg/hr have been noted from enthusiasts. Thrust to weight ratios of

between three and five have been achieved.

Lockwood Valveless Engine

The Lockwood valveless engine has been the most successful valveless pulsejet

developed in recorded history. The engine was investigated between during the 1960s

as a form of propulsion for vertical takeoff and landing (VTOL) aircraft. The engine is a

U-shape, with the exhaust bent around 180 degrees to direct both the intake and

exhaust thrusts in the same direction. A table of the final engine performance claims

can be seen in Table 4, however it should be noted that these values have never been

achieved using the patented design, specific fuel consumptions closer to 5kg/kg/hr

have been seen, with thrust results approximately 25% less than claimed. The

aerodynamic performance of the engine is also poor, in comparison to the Chinese and

FWE designs shown earlier.

Figure 12-Lockwood Prototype

(Lockwood 1957)


23

Table 4- Lockwood Performance Data

(Lockwood 1957)

Model HH 5.25-7

Valveless Engine

Military max thrust (lbs) 300

Maximum continuous (lbs) 280

Minimum idle (lbs) 30

Idle to mil. max time (secs) 0.1

Fuel/thrust (lb/lb/hr) 0.85

Dry weight (lbs) 30

Escopette

The Escopette was developed by the French research agency SNECMA (Societe

Nationale d'Etude et de Construction de Moteurs d'Aviation) in 1950. The engine was

the first developed with a rearward facing intake, and with expanding sections in the

exhaust.

Figure 13-Escopette Valveless Engine

The engines operating characteristics are different to a normal pulsejet, due to the

unique exhaust design and separation between the curved intake and the main engine.

The split intake allows the engine to behave as if its length were variable long during

the exhaust phase of the cycle and short during the intake phase. During expansion, it

treats the curved intake as a part of the effective length of the engine and uses it to

turn the escaping gas around and increase thrust (Ogorelec 2004). During the intake

cycle the curved section is not used. This reduces the effective length of the intake and

lets the engine inhale more easily.

The tailpipe is a series of steps of increasing section. Each transition from a straight


24

section into a diffusing section represents a point from which the pressure waves

travelling up and down the tube will reflect. Each of these waves reflects in an area of

varying temperature, and therefore they all travel at different speeds. The interaction

and timing of these waves are critical to the engines operation (Figure 13).

Figure 14 - Interaction of Escopette Pressure Waves

(Belfast University 1983)

The unique design of the engine means that it inhales twice for each expansion cycle,

with the aim of increasing the amount of cool air drawn into the exhaust section. This

increases the mass of the air in the exhaust and thus allows energy from the

combustion process to be converted more efficiently into thrust.

The original engine produced 108N of thrust, with a fuel consumption of 19.8kg/hr.

The engine however was extremely long at over 2.6m.

2.6.4 Exhaust Pipe Development

From the analysis of the pulsejet engines in Section 2.6.3, it can be seen that the

performance of a pulsejet engine is reliant on the behavior of the dominant waves in

the engines exhaust. Modifications of the engine exhaust characteristics can have a

dramatic effect on the engine performance. Studies by Artt and Balair in 1983 found

that altering the exhaust of a valved pulsejet engine could improve its performance by

up to 25%. The following section investigates the various exhaust designs,


25

characteristics and theories, in order to provide a knowledge base from which

modifications to the existing engines can be made.

Straight Pipe

Straight pipe exhausts are generally found on basic engines designed for first time

builders. The most common engine design to use a straight pipe is the Focused Wave

Engine, shown in Figure 15.

Figure 15 A Focused Wave (FWE) Pulsejet engine

(Beck, 2008)

The advantage of this type of exhaust is primarily ease of manufacture and cost

reduction, as commercially available pipe can be used, without the hassle of forming

conical sections. The section only operates on a single refraction wave returning from

the end of the exhaust, significantly reducing the engines throttle range, and thrust

output (Artt 1983).

Expansion Pipe

This type is the most common exhaust found on designs that produce reasonable to

high levels of thrust. Popular designs include the Lockwood-Hiller engine (Figure 16), as

well as the Chinese engine.


26

Figure 16 A Lockwood-Hiller style Pulsejet engine,

(Kontou 2007)

The most common justi

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