conceptual design of high-lift propeller systems for small electric aircraft

277 Pages·2016·4.19 MB·English

CONCEPTUAL DESIGN OF HIGH-LIFT PROPELLER
SYSTEMS FOR SMALL ELECTRIC AIRCRAFT
A Dissertation
Presented to
The Academic Faculty
by
Michael D. Patterson
In Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy in the
School of Aerospace Engineering
Georgia Institute of Technology
August 2016
Copyright (cid:13)c 2016 by Michael D. Patterson
CONCEPTUAL DESIGN OF HIGH-LIFT PROPELLER
SYSTEMS FOR SMALL ELECTRIC AIRCRAFT
Approved by:
Professor Brian J. German, Advisor Dr. Nicholas K. Borer
School of Aerospace Engineering Aeronautics Systems Analysis Branch
Georgia Institute of Technology NASA Langley Research Center
Professor Marilyn J. Smith Dr. Erik D. Olson
School of Aerospace Engineering Aeronautics Systems Analysis Branch
Georgia Institute of Technology NASA Langley Research Center
Professor Lakshmi N. Sankar Date Approved: 27 April 2016
School of Aerospace Engineering
Georgia Institute of Technology
To the One “who is able to do immeasurably more than all we ask or
imagine”1 and to my son Isaac who is living proof of His
immeasurable power
1Ephesians 3:20 (NIV)
ACKNOWLEDGEMENTS
This work would not have been completed without the help and encouragement of
many people. There is simply not sufficient time or space to acknowledge everyone
who has helped me make it through graduate school and finish this document.
Firstandforemost, mywife, Laura, hashelpedkeepmesanethroughoutthemany
stressful times and transitions that have occurred in my life since beginning grad
school. From providing me encouragement when things were getting overwhelming,
to picking up the slack around our home when I was slammed with work, to being
an awesome mother to our kids, she has helped me more than any other person to
complete this work.
All the other members of my family have also provided love, support, encour-
agement, and much-needed diversions from work throughout grad school. My boys,
William and Isaac, have helped me keep perspective on what’s really important in
life (particularly recently). The rest of my extended family, not least of which are my
parents and parents-in-law, have also been great sources of support throughout my
life and in particular through this last year.
Perhaps the single most influential person in helping to guide the general direction
ofmyresearchhasbeenMarkMooreofNASALangley. Iwouldcertainlynotbewhere
I am today physically or professionally if Mark had not taken a chance in funding my
advisor and one of his young grad students to help with the Zip Aviation study back
nearly five years ago. Mark has also been instrumental in promoting electric aircraft
andon-demandmobilityresearchatNASA,andtheSCEPTORproject(amongmany
others) simply would not have happened without his tireless efforts.
I would also like to thank my entire thesis committee for their guidance, feedback,
iv
and inspiration. I am very thankful for Dr. German’s decision to bring me into
his research group and for the many conversations and meetings we had together
throughout my time in grad school. He has been a great advisor, and I am certainly a
betterresearcher,engineer,andwriterbecauseofhim. Dr.Borerhasbeenanawesome
mentor at NASA. Virtually every aspect of this dissertation has come either directly
or indirectly from conversations I’ve had with him. Without his encouragement and
pragmatic advice, I would not have completed this document. It was in Dr. Sankar’s
class where I first learned about rotor design, and many elements of this document
would likely not have come about without his teaching. Dr. Smith’s teaching and
technical excellence have pushed me to perform as high-quality work as possible. I
have been inspired by Dr. Olson’s work in applying corrections to lower-order tools
to obtain more accurate results, and I emulate some of his general techniques in this
document.
Big thanks are also due to all the members of the “German Research Group”
(formal and honorary) for their friendship, doubt raising, humor, and all-around
awesomeness throughout grad school. Y’all made life in asbestos-laden ESM and
the dungeon of Weber much more enjoyable than it could have been. David Pate
deserves special thanks, as I’m not sure if I would have made it through qualifying
exams without him.
The OVERFLOW CFD results presented in Chapter III would not have been
possible without Dr. Joe Derlaga of NASA Langley. He was quite patient with me
in helping get me set up to run cases for which I am very thankful. His practical
aerodynamic knowledge has been a huge asset to me and the broader SCEPTOR
project team. Joe has been a great colleague, and I look forward to continuing to
work along side him into the future.
IwouldalsoliketothanktheentireSCEPTORprojectteamincludingeveryoneat
Joby Aviation, Empirical Systems Aerospace (ESAero), and across NASA. In terms
v
of technical content in this document, the FUN3D CFD results from the LEAPTech
configuration discussed in Chapter III were performed by Karen Deere, Salley Viken,
and Steve Bauer of NASA Langley, and the STAR-CCM+ CFD results for the same
configuration were run by Alex Stoll of Joby Aviation. I’m also grateful for Alex’s
help in tracking down and discussing various simplified methods of estimating lift
increases due to propeller blowing. Brandon Litherland of NASA Langley performed
the parasite drag estimation of the SCEPTOR aircraft without flaps and helped me
get up and running in VSPAero.
I would also like to acknowledge the funding that has made this work possible.
First, theNASAAeronauticsScholarshipProgramprovidedfundingformyfinalyears
on campus. Second, much of this work has been performed while I have been working
at NASA Langley Research Center on the Convergent Aeronautics Solutions (CAS)
and Transformational Tools and Technologies (TTT) Projects, which are both part of
the NASA Aeronautics Research Mission Directorate’s Transformative Aeronautics
Concepts Program.
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TABLE OF CONTENTS
ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . iv
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii
LIST OF SYMBOLS OR ABBREVIATIONS . . . . . . . . . . . . . . . xvii
SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi
I INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Electric Aircraft Propulsion . . . . . . . . . . . . . . . . . . . 2
1.1.2 Integrated, Distributed Propulsion and Distributed Electric
Propulsion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.1.3 Past NASA Distributed Electric Propulsion Research . . . . 14
1.1.4 Potential Benefits of Distributed Electric Propulsion for Small
Aircraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.2 NASA’s SCEPTOR Project . . . . . . . . . . . . . . . . . . . . . . . 25
1.2.1 Project Background . . . . . . . . . . . . . . . . . . . . . . . 25
1.2.2 Distributed Electric Propulsion System . . . . . . . . . . . . 26
1.2.3 Research Challenges . . . . . . . . . . . . . . . . . . . . . . . 29
1.3 Scope and Organization of this Thesis . . . . . . . . . . . . . . . . . 30
1.3.1 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . 30
1.3.2 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
II TRADITIONALPROPELLERANALYSISANDDESIGNMETH-
ODS AND PROPELLER-WING INTERACTION . . . . . . . . . 33
2.1 A Brief Overview of General Aerodynamic Modeling Techniques for
Lifting Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.2 Propeller Analysis and Design Methods . . . . . . . . . . . . . . . . 35
2.2.1 Momentum Theory . . . . . . . . . . . . . . . . . . . . . . . 35
2.2.2 Blade Element Momentum Theory . . . . . . . . . . . . . . . 39
vii
2.2.3 Vortex Theory and Minimum Induced Loss Design Methods . 42
2.3 Propeller-Wing Interaction . . . . . . . . . . . . . . . . . . . . . . . 45
2.3.1 Propeller Slipstream Flow Characteristics . . . . . . . . . . . 45
2.3.2 General Impacts of Tractor Propellers on Downstream Wings 47
2.3.3 Modeling Propeller-Wing Interaction . . . . . . . . . . . . . 51
2.3.4 Desire for New Theory . . . . . . . . . . . . . . . . . . . . . 58
2.4 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
III A SIMPLE HIGH-LIFT PROPELLER LIFT AUGMENTATION
THEORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.1 A Two-Dimensional Model for Predicting Wing Lift Augmentation
from High-Lift Propellers . . . . . . . . . . . . . . . . . . . . . . . . 61
3.1.1 Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.1.2 General Model . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.1.3 Specific Propeller Installations . . . . . . . . . . . . . . . . . 66
3.1.4 Extension to Three Dimensions . . . . . . . . . . . . . . . . . 71
3.1.5 Intermediate Summary of the Two-Dimensional Model . . . . 75
3.2 Accounting for Propeller Slipstream Height . . . . . . . . . . . . . . 77
3.2.1 Quantifying Slipstream Height Impacts . . . . . . . . . . . . 80
3.2.2 Modifying the Simple Theory . . . . . . . . . . . . . . . . . . 98
3.3 Comparison of Model to Experimental Results and Other Methods . 100
3.3.1 LEAPTech . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
3.3.2 Kuhn and Draper Experiments . . . . . . . . . . . . . . . . . 105
3.3.3 Gentry et al. Experiments . . . . . . . . . . . . . . . . . . . 107
3.3.4 Summary of Simple Models . . . . . . . . . . . . . . . . . . . 111
3.4 Implications of Model . . . . . . . . . . . . . . . . . . . . . . . . . . 112
3.5 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
IV A SIMPLE METHOD FOR HIGH-LIFT PROPELLER CONCEP-
TUAL DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
4.1 Motivation for a New Propeller Design Method . . . . . . . . . . . . 116
viii
4.2 High-Lift Propeller Design Method . . . . . . . . . . . . . . . . . . . 119
4.2.1 Blade Design for a Desired Induced Velocity Distribution . . 120
4.2.2 Example Propeller Design and Comparison to a Minimum In-
duced Loss Propeller . . . . . . . . . . . . . . . . . . . . . . 128
4.2.3 Additional Comments on the Optional Steps . . . . . . . . . 138
4.3 Cautionary Statements . . . . . . . . . . . . . . . . . . . . . . . . . 142
4.4 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
V DETERMINING THE DESIGN POINT FOR THE HIGH-LIFT
PROPELLERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
5.1 Approach Considerations . . . . . . . . . . . . . . . . . . . . . . . . 145
5.1.1 Regulations Related to Stall and Approach Speeds . . . . . . 146
5.1.2 ExplorationofLiftCoefficientMarginandPotentialApproach
Profiles of Aircraft with High-Lift Propellers . . . . . . . . . 153
5.2 Altitude Considerations . . . . . . . . . . . . . . . . . . . . . . . . . 188
5.3 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
VI SELECTING THE NUMBER AND POSITION OF HIGH-LIFT
PROPELLERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
6.1 High-Lift Propeller Installation Considerations . . . . . . . . . . . . 194
6.1.1 Propeller Orientation Relative to the Wing . . . . . . . . . . 194
6.1.2 Propeller Placement Relative to the Wing . . . . . . . . . . . 196
6.2 Design Space Exploration for Selecting the Number of High-Lift Pro-
pellers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
6.2.1 Design Assumptions and SCEPTOR Aircraft Information . . 202
6.2.2 Design Space Exploration Process . . . . . . . . . . . . . . . 205
6.2.3 Linking the Process to Wing Design . . . . . . . . . . . . . . 219
6.3 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
VIICONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
7.1 Summary and Implications of Results . . . . . . . . . . . . . . . . . 226
7.1.1 Summary of Contributions . . . . . . . . . . . . . . . . . . . 232
7.2 Potential Directions for Further Research . . . . . . . . . . . . . . . 233
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APPENDIX A — OVERFLOW SIMULATION RESULTS AND SUR-
ROGATE MODEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
VITA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
x