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A Process for the Design and Manufacture of Propellers forSmall Unmanned Aerial VehiclesbyBrian David RutkayA thesis submitted to the Faculty of Graduate and PostdoctoralAffairs in partial fulfillment of the requirements for the degree ofMaster of Applied ScienceinAerospace EngineeringCarleton UniversityOttawa, Ontario 2014, Brian David Rutkay

AbstractThe objective of this research was to develop a process for the design and manufacture ofmission- and aircraft-specific propellers for small unmanned aerial vehicles. Thisobjective was met by creating a computer program to design a propeller that meets userdefined aircraft performance requirements within the limitations of the motor, material,and manufacturing methods. The use of additive manufacturing (3D printing) in makingflightworthy propellers was explored through material testing and by manufacturingtrials. By testing the propellers in simulated flight conditions, it was found that thepropellers generated nearly the expected design thrust, but a series of manufacturing andinstrumentation issues prevented a complete evaluation of their performance. Testing wassufficient to demonstrate the feasibility of flightworthy propellers produced throughadditive manufacturing. Future work for the further development of the design programwas also outlined.ii

AcknowledgementsThis work was completed over the course of three years but probably would havetaken twice as long had it not been for the help of many individuals. I’d like to thank thedepartment of Mechanical and Aerospace Engineering lab staff – Steve Truttmann,Stephan Bilijan and David Raude – for their assistance during material and wind tunneltesting. I’d also like to thank Nagui Mikhail for his advice and for allowing me access tothe Department of Electronics’ resources throughout the development of theinstrumentation. Throughout my undergrad and graduate studies I’ve been grateful forAlex Proctor, Kevin Sangster and Ian Lloy for allowing me to work in the departmentmachine shop and patiently helping me produce what I’ve designed. My experiences inthe machine shop influenced everything I designed for my thesis and am grateful for theopportunities I had to learn from you.I’d like to thank all of my friends for their support throughout the course of thisproject. There are a few people I’d like to recognize in particular for their help on keyaspects of this work. Hristo Valtchanov’s advice on layout of my thesis led to adrastically better final product than I could have hoped for had I done it my way. I’d liketo thank John Polansky for his advice and support but in particular helping me polish mydefense presentation and selecting the appropriate firearms and ammunition for theballistic pendulum test. I’m grateful for Ryan Anderson for showing me some of thesheet metal fabrication practices he learned while working in the aviation industry and forthe great discussions on aircraft and mechanical design we had, especially back inundergrad when I was starting to develop my mechanical design skills. I’d like to thankJonathan Wiebe for his help on manufacturing the test rig - luckily for me even after he’diii

spent a full day work on his own research work he was willing to help me assemble andtroubleshoot problems with the test rig - and for his advice while I was writing the designprogram. I also need to thank Aaron Parton for the numerous shawarma-and-beerdiscussions during development and for “Jarome” which was used during the ballisticpendulum tests.I definitely need to thank my mom, dad and brother for putting up with me while Iwas working on my thesis, for the late-night rides home, and for helping me edit andformat my thesis. I owe a huge amount of thanks to my dad for spending long days withme in the wind tunnel rather than the golf course over his summer vacation. As rough astesting went, I really enjoyed the opportunity to work with you in the lab and I think it’ssafe to say it’d have been even more hellish – and possibly never completed - had it notbeen for your help.Most of all, I’m incredibly grateful for the unwavering and seemingly limitlesspatience, encouragement and support of my supervisor, Dr. Jeremy Laliberté. Thisproject took much longer than planned and grew significantly in scope, and few wouldhave been able to maintain your high level of enthusiasm throughout the course of theproject despite all of the difficulties I encountered. Between getting me into the master’sprogram to spending late nights looking over my thesis, thank you so very much for theamazing opportunities and help you’ve provided over the last few years.iv

Table of ContentsAbstract . iiAcknowledgements . iiiTable of Contents . vList of Tables . xiiiList of Appendices . xviiNomenclature . xviii1 Chapter: Introduction. 221.1Motivation . 221.2Objectives. 221.3Methods . 221.4Scope . 242 Chapter: Literature Review . 252.1Overview . 252.2Small Unmanned Aerial Vehicles . 252.3Propeller Design . 282.3.1Propeller Operation . 282.3.2Design Methods . 332.3.2.1Early Propeller Design Approaches . 332.3.2.2Traditional Methods of Design . 352.3.2.3UAV Propeller Design . 382.3.32.4Airfoils for Propellers . 402.3.3.1Propeller Airfoil Series . 402.3.3.2Airfoil Data . 43Design and Testing Requirements for UAV Propellers . 48v

2.4.1Certification Requirements . 482.4.1.1Federal Aviation Regulations - Part 35 (FAR 35). 522.4.1.2ASTM F2506 Standard Specification for Design and Testing of Light SportAircraft Propellers. 562.4.22.5Other Design Requirements . 59Materials and Manufacturing . 622.5.1Overview of Materials for Propellers . 622.5.1.1Wood . 622.5.1.2Metal . 642.5.1.3Composites and Plastics . 642.5.1.4Reinforced Plastics . 662.5.2Additive Manufacturing . 662.5.2.1Overview of Additive Manufacturing . 662.5.2.2Additive Manufacturing of Aerospace Components . 683 Chapter: Development of the Propeller Design Program . 713.1Introduction . 713.2Design Constraints . 723.2.1Propeller Size and Speed Constraints . 733.2.2Aircraft Performance . 733.2.3Powerplant Characteristics . 753.2.4Airfoil Family . 753.2.5Lift Coefficient Conditions . 763.2.6Manufacturing Method and Material Properties . 773.2.7Methods of Blade Design . 783.33.3.1Initial Propeller Sizing . 78Single-Point Performance Method. 79vi

3.3.23.4Scoring Process . 85Detailed Propeller Blade Design . 873.4.1Optimum Blade Loading Conditions . 873.4.2Thrust Coefficient and Power Coefficient Modes . 913.4.3Blade Design . 923.4.4Simplified Blade Structural Analysis. 943.4.5Sweep at Speed . 993.4.6Trailing Edge Correction . 1003.4.7Selecting an Airfoil for a Blade Station . 1033.5Propeller Blade Selection . 1043.6Detailed Structural Analysis of Propeller Blades . 1053.6.1Aerodynamic Loads . 1053.6.2Mass Loads . 1074 Chapter: Material Testing . 1114.1Introduction . 1114.1.1The Need for Material Testing. 1114.1.2Tensile Stress Rupture . 1124.1.3Objectives of Material Testing . 1134.2Material Testing . 1144.2.1Overview. 1144.2.2Materials Tested. 1154.2.3Guidance for Testing . 1164.2.4Test Specimen Design . 1164.3Tensile Testing . 1174.3.1Overview. 1174.3.2Test Equipment & Procedures . 117vii

4.3.3Round 1 Tensile Testing . 1184.3.3.1Summary . 1184.3.4Lessons Learned From Round 1 Testing . 1224.3.5Round 2 Tensile Testing . 1234.3.5.1Summary of Testing . 1234.3.5.2Lessons Learned From Round 2 Testing. 1294.4Stress Rupture Testing . 1314.4.1Overview. 1314.4.2Initial Testing . 1314.4.3Stress Rupture Test Rig . 1314.4.4Stress Rupture Testing . 1334.4.5Effect of Tensile Stress on Strength. 1344.5Conclusions . 1345 Chapter: Design and Testing of the Wind Tunnel Propeller Test Rig . 1375.1Introduction . 1375.2Propeller Test Stand . 1385.2.1Overview. 1385.2.2Review of Existing Test Rigs . 1385.2.3Design and Operation of the Test Stand . 1405.2.3.1Measurement Head. 1415.2.3.2Blade-Off Arrestor . 1425.2.3.3Frame . 1435.2.3.4Nacelle and Pylon . 1445.2.4Test Stand Design and Construction Details . 1455.2.4.1Water-Jet Cutting and CNC machining . 1455.2.4.2Standard Aircraft Hardware . 146viii

5.2.5Instrumentation . 1475.2.5.1Strain Gauge Installation . 1475.2.5.2Measuring Strain Gauge Voltages . 1495.2.5.3Calibration . 1505.2.6Tunnel Calibration . 1525.2.6.1Effect of Test Stand. 1525.2.6.2Wind Tunnel Interference . 1555.3Shroud . 1585.3.1Overview. 1585.3.2Shroud Testing . 1595.3.2.1Kinetic Energy of an Ejected Propeller Blade . 1595.3.2.2Drop Tower Testing . 1625.3.2.3Ballistic Pendulum Testing . 1636 Chapter: Process Testing . 1686.1Introduction . 1686.2Overview of Testing. 1686.3Propeller Design . 1736.4Propeller Manufacturing . 1766.5Propeller Performance Testing . 1796.5.1Initial Propeller Testing . 1796.5.2Wind Tunnel Testing . 1796.5.2.1Test Technique . 1806.5.2.2Data Collection . 1816.6Data Reduction . 1846.7Results . 1856.7.1As-Manufactured Propeller Performance . 185ix

6.7.2Epoxy-Coated Propeller . 1886.7.3Meeting Mission Requirements . 1907 Chapter: Conclusions and Recommendations . 1927.1Conclusions . 1927.1.1Thoughts on the Design of the Propeller . 1927.1.2Thoughts on Materials and Manufacturing . 1937.1.3Thoughts on Wind Tunnel Testing . 1947.1.3.1Thrust and Torque Transducers . 1947.1.3.2Instrumentation . 1957.1.3.3Overall Approach to Testing . 1967.1.47.2Overall Feasibility. 196Future Work . 1977.2.1Correcting Issues Identified During Testing . 1977.2.1.1Improved Structural Analysis Methods and Integration . 1977.2.1.2Improved Transducers and Instrumentation . 1977.2.2Improvements to the Process . 1987.2.2.1Interfacing XFOIL with the Design Program . 1987.2.2.2Modelling the Airflow Around the Airframe . 1987.2.2.3Externally-Reinforced Blade Structure . 1997.2.2.4Designing Flexible Propellers or Ground-Adjustable Propellers . 1997.2.2.5Complete Modelling of a UAV’s Propulsion System . 2007.2.2.6Improved Instrumentation . 2007.3Implications of Work . 2017.3.1Use for Manned-Aircraft Propeller Design. 2017.3.23D Printed Mission-Specific UAVs. 201x

Bibliography . 203Appendix AAircraft Performance Methods . 219A.1Required and Maximum Thrust. 219A.2Operating Assumptions . 219A.3Take-Off . 220A.4Best Rate of Climb . 230A.5UAV Performance in Cruise . 236A.5.1Maximum Endurance, Range, and Design Cruise Speed . 237A.5.1.1Maximum Endurance . 237A.5.1.2Maximum Range . 237A.5.1.3Design Cruise Speed. 239A.5.2Thrust Required in Cruise . 239A.5.2.1Normal Required Thrust . 239A.5.2.2Maximum Required Thrust . 240A.5.2.2.1 Additional Thrust – Climb in Cruise . 240A.5.2.2.2 Additional Thrust – Turning Flight . 241A.5.3Comparison of Predicted Cruise Performance to Flight Test Data . 242Appendix BB.1Brushless Direct-Current Motor Analysis & Optimization . 247Basic BLDC Motor Analysis. 247B.1.1Shaft Speed. 248B.1.2Mechanical Torque. 249B.1.3Shaft Power . 250B.1.4Thermal Effects . 250B.2Simplified BLDC Motor Optimization. 252B.2.1Optimum Shaft Power with Thermal Effects Neglected . 252B.2.2Optimum Shaft Power with Thermal Effects Included . 254xi

B.3Comparing Predicted and Actual Motor Performance . 255B.3.1Predicted and Actual Performance of the S-4035-460KV Motor . 257B.3.2Predicted and Actual Performance of the S-5535-190KV Motor . 259B.3.3Conclusions . 259Appendix CCalculations for Blade Sizing and Design . 266C.1Propeller Sizing . 266C.2Determining the Initial Maximum and Minimum Induced Velocity . 267C.3Single Point Method of Estimating Thrust and Power Coefficient . 268C.4Detailed Blade Shaping Process . 272C.5Estimating Propeller Performance Using Both Single-Point and Full-Blade Methods274xii