Coaxial Rotary-Wing Mini Aerial Vehicle Aeromechanics

381 Pages·2010·31.92 MB·English

Coaxial Rotary-Wing
Mini Aerial Vehicle
Aeromechanics
Alexander P. K. Hall
A thesis submitted in fulfillment
of the requirements for the degree of
Doctor of Philosophy
UAV Group
School of Aerospace, Mechanical and Mechatronic Engineering
The University of Sydney
March 2009
Declaration
I hereby declare that this submission is my own work and that, to the best of my knowl-
edge and belief, it contains no material previously published or written by another person
nor material which to a substantial extent has been accepted for the award of any other
degree or diploma of the University or other institute of higher learning, except where due
acknowledgement has been made in the text.
Alexander Hall
30 March 2009
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Abstract
Alexander Hall Doctor of Philosophy
The University of Sydney March 2009
Coaxial Rotary-Wing Mini Aerial
Vehicle Aeromechanics
This thesis presents novel methodology for analysing the aeromechanical performance of
small coaxial helicopters for use as Unmanned Aerial Vehicles. Fundamentally, the focus of
this work is on developing a simple yet robust analysis methodology for investigating the
aeromechanicalbehaviourofhighlydynamiccoaxialrotors. Inparticular, focusisplacedon
creating a method which is computationally inexpensive yet retains accuracy. By retaining
these objectives throughout the development process, a design tool with characteristics
which are beneficial to platform design optimisation has been created.
Specifically, a Proxflyer type rotorcraft was chosen as the desired target of investigation.
This platform places particularly challenging requirements on any analysis methodology
used. The combination of highly dynamic flapping coaxial rotors, which are positioned
in close proximity, places high demands on aerodynamic modelling. This is made more
challenging by low Reynolds number at which the rotors are operating. In this region,
there is little known about the flow characteristics which drive rotor performance. Original
analysis methodology has been developed to encapsulate these effects.
Newanalysismethodsformodellingcoaxialrotorinteractionaswellashighlydynamicrotor
flapping has also been developed. A method which accounts for the interaction between
coaxial rotors has been developed for use within Blade Element Momentum Theory. This
method is characterised as Velocity Augmentation, which operates by mapping rotor effects
between the coaxial rotors. Verification of this theory was conducted and shows that the
computational model agrees well with experimental tests. To account for complex rotor
dynamics, a model which represents the flapping of the rotor blades was developed. This
model allows the rotor characteristics which effect flapping performance to be investigated.
The developed analysis methodology has been applied to the study of the stability, control-
lability and efficiency of Proxflyer type rotorcraft. Two studies centred on this rotorcraft
type show that the developed analysis can be used for configuration design and optimisa-
tion. Firstly, an existing rotorcraft configuration has been studied with improvements seen
in both stability and efficiency. Secondly, a new rotorcraft configuration has been analysed
withresultsleadingtogoodperformanceinstability, controllabilityandefficiency. Through
these studies, the new analysis methodology is shown to give rise to many new avenues of
research, and also provides important new techniques for the analysis and design of Coaxial
Rotary-Wing Mini Aerial Vehicles.
Project Publications
Full Paper Reviewed
Hall, A., Wong, K.C. and Auld, D., “Coaxial Rotor Interaction Modelling Using Blade El-
ement Momentum Theory”, Proceedings of the 7th Australian Pacific Vertiflite Con-
ference on Helicopter Technology, Melbourne, Australia, 9 - 12 March, 2009
*Received best paper award.
Hall, A. and Wong K.C., “Coaxial Helicopter with Fully Controlled Flapping Feedback
Rotors”, Proceedings of the 3rd Australasian Unmanned Air Vehicles Conference,
Melbourne, Australia, 9 - 12 March, 2009
Hall, A. and Wong, K.C., “Development of an Analysis Package for Increased Stability
Rotary-Wing Micro Air Vehicles”, Proceedings of the 6th Australian Vertiflite Con-
ference on Helicopter Technology, Melbourne, Victoria, March 19-22, 2007
Extended Abstract Reviewed
Hall, A., Wong, K.C. and Auld, D., “Analysis and Conceptual Design of a Novel MAV
Rotorcraft”,Proceedingsofthe34thEuropeanRotorcraftForum,Liverpool,England,
2008
Hall, A., Wong, K.C. and Auld, D., “Coaxial Aero-Mechanical Analysis of MAV Rotor-
craft with Rotor Interaction for Optimisation”,Proceedingsofthe12thAIAA/ISSMO
Multidisciplinary Analysis and Optimization Conference, Victoria, Canada, 2008
Hall, A., Wong, K.C. and Auld, D., “Simple Rotor Dynamics Analysis of MAV Rotorcraft
for Optimisation”, Proceedings of the 11th AIAA/ISSMO Multidisciplinary Analysis
and Optimization Conference, Portsmouth, Virginia, 2006, AIAA-2006-7076
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Acknowledgements
Over the past four years I have both enjoyed and hated the process of completing my PhD.
Although I have always thoroughly enjoyed working on coaxial helicopters, I almost always
took the road less travelled. And with the support and guidance of my supervisors, KC and
Doug, have turned my ideas into something useable. For this I thank them.
I appreciate the encouragement and support that my family has shown over the never-
ending last four years. Mum, for always listening to me (for better or worse) when I needed
it, as well as for being put through the painful task of reading all my draft chapters. James,
for annoying me as an older brother should. Liz and Pat, for coming to Sydney to distract
me from my project, always when I needed it. And, Dette and Sarah for giving me the
drive to get a real job.
Alana has my deepest thanks and appreciation for her support through the crunch time of
this project. She has given me someone to laugh, smile and joke with, as well listening to
my occasional rants, and telling me that I am just being silly. It certainly has been a much
easier and more enjoyable ride with her.
To all my friends who have supported me over the never ending four years, I thank you. In
particular, Brettfor being mycoffee dealer; andKaneandStu (Alexander)fortempting me
to distraction, oh so many times. My office-mates (Peter, Josh, Angus, Juan and James)
over the years have provided me with not only good company, but a wall to bounce ideas
off. This is especially useful when you have created one too many problems for yourself.
And lastly, but not least, Stuart and Duncan for distracting me so much, that I needed the
full four years!
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The helicopter approaches closer than any other vehicle to fulfillment of mankind’s ancient
dreams of the flying horse and the magic carpet.
Igor Sikorsky
Engineers like to solve problems. If there are no problems handily available, they will
create their own problems.
Scott Adams
Contents
Declaration i
Abstract ii
Project Publications iii
Acknowledgements iv
Contents vi
List of Figures xiv
List of Tables xxiii
List of Symbols xxv
List of Abbreviations xxviii
1 Introduction 1
1.1 Thesis Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.3 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Rotary-Wing Aircraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1 Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1.1 Conventional . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.1.2 Coaxial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
vi
CONTENTS vii
1.2.1.3 Tandem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.1.4 Multi-Rotor . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.2 Rotary-Wing UAVs . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Proxflyer Rotorcraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 Rotary-Wing Conventions and Definitions . . . . . . . . . . . . . . . . . . . 9
1.5 Thesis Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.5.1 Summary of Completed Work . . . . . . . . . . . . . . . . . . . . . . 10
1.5.2 Chapter Layouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.5.2.1 Chapter 2 - Background and Motivation. . . . . . . . . . . 11
1.5.2.2 Chapter 3 - Blade Element Momentum Theory . . . . . . . 12
1.5.2.3 Chapter 4 - Coaxial Rotor Interaction Modelling . . . . . . 12
1.5.2.4 Chapter 5 - Interaction Model Verification . . . . . . . . . 12
1.5.2.5 Chapter 6 - Blade Flap Modelling . . . . . . . . . . . . . . 12
1.5.2.6 Chapter 7 - Coaxial Rotorcraft Analysis . . . . . . . . . . . 13
1.5.2.7 Chapter 8 - Design Studies . . . . . . . . . . . . . . . . . . 13
1.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2 Background and Motivation 14
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2 Problem to Solve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3 Configuration Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.4 Coaxial Helicopter Configuration . . . . . . . . . . . . . . . . . . . . . . . . 18
2.4.1 Existing Aircraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.4.2 Benefits and Drawbacks . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.4.3 Configuration Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.5 Helicopter Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5.1 Rotor Aerodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5.2 Rotor Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5.3 Rotorcraft Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5.4 Analysis Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.6 Design Optimisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
CONTENTS viii
3 Blade Element Momentum Theory 36
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2 Basic Blade Element Momentum Theory . . . . . . . . . . . . . . . . . . . . 37
3.2.1 Hover and Vertical Flight . . . . . . . . . . . . . . . . . . . . . . . . 40
3.2.2 Momentum Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.2.3 Aerodynamic Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.2.4 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.2.5 Example Implementation of Basic Theory . . . . . . . . . . . . . . . 45
3.3 Tip Loss Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.4 Multiple Blade Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.5 Translational Flight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.6 Aerodynamic Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.7 Problem Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
4 Coaxial Rotor Interaction 63
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.1.2 Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.2 Background and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.2.1 Previous Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.2.2 Available Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.2.2.1 Empirical Relations . . . . . . . . . . . . . . . . . . . . . . 65
4.2.2.2 Vortex Methods . . . . . . . . . . . . . . . . . . . . . . . . 67
4.2.2.3 Additional Methods . . . . . . . . . . . . . . . . . . . . . . 68
4.2.2.4 BEMT Methods . . . . . . . . . . . . . . . . . . . . . . . . 68
4.2.3 Summary and Method Choice . . . . . . . . . . . . . . . . . . . . . . 70
4.3 Overview of Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.4 Rotor Interaction Method within BEMT . . . . . . . . . . . . . . . . . . . . 73
4.5 Simple Test Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.6 Method Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
CONTENTS ix
4.6.1 Centred Around Hover . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.6.2 Static Streamtube . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.6.3 Steady State Flow Between Rotors . . . . . . . . . . . . . . . . . . . 82
4.6.4 Incompressible Inviscid Flow . . . . . . . . . . . . . . . . . . . . . . 83
4.7 Full Method Explanation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.7.1 Convergence Procedure Outline . . . . . . . . . . . . . . . . . . . . . 83
4.7.2 Geometric Calculation Outline . . . . . . . . . . . . . . . . . . . . . 84
4.7.3 Geometric Calculation Explanation . . . . . . . . . . . . . . . . . . . 87
4.7.3.1 Azimuth Location . . . . . . . . . . . . . . . . . . . . . . . 87
4.7.3.2 Flap Angles . . . . . . . . . . . . . . . . . . . . . . . . . . 88
4.7.3.3 Radial Location . . . . . . . . . . . . . . . . . . . . . . . . 89
4.7.3.4 Stream Contraction Angle . . . . . . . . . . . . . . . . . . 94
4.7.3.5 Vertical Separation . . . . . . . . . . . . . . . . . . . . . . 96
4.7.3.6 Radial Interpolation . . . . . . . . . . . . . . . . . . . . . . 98
4.7.4 Implementation Method . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.7.4.1 Pre-Loop Calculations . . . . . . . . . . . . . . . . . . . . . 100
4.7.4.2 Loop Calculations . . . . . . . . . . . . . . . . . . . . . . . 100
4.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
5 Interaction Model Verification 105
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.2 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
5.2.1 Rotor Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
5.2.2 Rotor Drive Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . 109
5.2.3 Load Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
5.2.4 Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
5.2.5 Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
5.3 Coded Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
5.4 Test Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
5.5 Post Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
5.6 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123