DESIGN AND IMPLEMENTATION OF A LOW COST THERMAL SOARING SYSTEM FOR UNINHABITED AIRCRAFT A Thesis by Zachary Robert Timm Hazen Bachelor of Science, University of Colorado Boulder, 2007 Submitted to the Department of Aerospace Engineering and the faculty of the Graduate School of Wichita State University in partial fulfillment of the requirements for the degree of Master of Science May 2012 © Copyright 2012 by Zachary Hazen All Rights Reserved DESIGN AND IMPLEMENTATION OF A LOW COST THERMAL SOARING SYSTEM FOR UNINHABITED AIRCRAFT The following faculty members have examined the final copy of this thesis for form and content, and recommend that it be accepted in partial fulfillment of the requirement for the degree of Master of Science with a major in Aerospace Engineering. _________________________________ Leonard Scott Miller, Committee Chair _________________________________ Kamran Rokhsaz, Committee Member _________________________________ John Watkins, Committee Member iii Flock together, soar forever. iv ACKNOWLEDGMENTS Many thanks are due to several individuals that made my pursuit of this work possible. Kevin Hagen provided manufacturing and operations support well beyond his age. I hope that you learned and enjoyed crashing planes with me, Kevin. You are ahead of the curve. Thanks to Dr. Miller for allowing a student with a big idea to bury himself in it. I could not have learned as much as I have without your guidance, support, and genuine enthusiasm (which can be rare in professionals in your position). Thanks to Jimmy Prouty of Hangar 18 UAV, who provided ground crew support, donated a vehicle to the project, helped me build prototypes, and flew my UAVs on several occasions when my head was buried in the ground computer data. Jimmy you and your planes rock. Period. Thanks to Ashley Archiopoli for encouraging me to pursue my Master’s Thesis and supporting my efforts. Thanks to Steve Morris of MLB Co for providing helpful insight into the problem of UAV soaring, helping me find a suitable test site in Northern California, and always offering any resources that could help me in my crazy pursuit to get robotic birds soaring together. Many thanks to Austin Howard and Jen Founds for providing ground crew support. I’m glad we finally got your Jetta out of the cow farm mud, Jen. Thanks to Jordan Jensen for building wings for the CoSoar III and IV. I hope you enjoyed learning the vacuum bagging process and get to apply it to a cool model in the future. Thanks to my committee for making time for me in a compressed schedule for my oral defense, and providing valuable feedback on my work on the whole. Huge Thanks to Meabon Burns, PE, for not only editing my work over many hours of her personal time, but for helping me stay focused on the goal at hand. Your work ethic is contagious. Thanks to Michael Allen and Dan Edwards. You guys helped inspire me to work on autonomous soaring. Finally, I would like to thank all of the students I met while assistant teaching at Wichita State. You guys sure know how to mess up a lab but you also do a great job keeping me grounded with the perspective and unspoiled imagination that undergraduate aerospace students possess – looking skyward and thinking of your senior design/DBF plane. It was a pleasure working with each and every one of you. v ABSTRACT The use of atmospheric updrafts as an energy source for long endurance flight has proven to be extremely advantageous for birds, remote control sailplanes, and manned soaring vehicles. Recent research conducted by Michael Allen at NASA and Dr. Dan Edwards at North Carolina State University has demonstrated the viability of using a UAV to search for, detect, and gain altitude using thermal updrafts. This approach can be taken a step further by introducing multiple cooperating vehicles to reduce the time spent searching for thermal lift while simultaneously increasing the time spent in thermal lift gaining altitude and/or saving fuel. UAV missions calling for multiple vehicles can use this approach to reduce the demand for on board energy storage by using environmental energy more effectively than a vehicle flying alone. This research aims to complement existing autonomous soaring efforts by developing a low cost thermal soaring system that is capable of working with single or multiple cooperating vehicles to find and utilize thermal updrafts. Early simulations developed to validate this idea have given rise to further analysis and experimentation with two custom airframes, each equipped with instruments to detect updrafts and autonomous capabilities to test cooperative soaring algorithms in the real world. The system developed used a sub $1000 commercial off- the-shelf autopilot and custom ground control software to achieve many autonomous soaring flights with a single vehicle. Several flights with two autonomous vehicles were also performed and cooperative behavior was demonstrated. vi TABLE OF CONTENTS Chapter Page 1. BACKGROUND .................................................................................................................. 1 1.1 Energy Demands on Small UAVs ....................................................................................1 1.2 Thermal Soaring in Manned Aircraft and Nature ..............................................................3 1.3 Previous Work in UAV Thermal Soaring .........................................................................4 2. AUTONOMOUS SOARING IN SIMULATION .................................................................. 7 2.1 Motivation .......................................................................................................................7 2.2 Simulation Architecture ...................................................................................................7 2.3 Modeling the Convective Boundary Layer .......................................................................8 2.4 Modeling the UAV and Autopilot .................................................................................. 11 2.5 Thermal Soaring Controller Development ...................................................................... 13 2.6 Simulation Parameters and Results................................................................................. 19 3. AUTONOMOUS SOARING IN PRACTICE ...................................................................... 26 3.1 Experiment Goals and Limitations ................................................................................. 26 3.2 Hardware Selection ........................................................................................................ 28 3.3 Software Development ................................................................................................... 35 4. RESULTS ........................................................................................................................... 39 4.1 Single Vehicle Soaring................................................................................................... 39 4.2 Cooperative Soaring....................................................................................................... 45 5. CONCLUSIONS ................................................................................................................. 49 5.1 Review of Major Findings.............................................................................................. 49 5.2 Future Work .................................................................................................................. 50 5.3 Lessons Learned ............................................................................................................ 52 REFERENCES ......................................................................................................................... 55 vii TABLE OF CONTENTS (continued) Chapter Page APPENDIX .............................................................................................................................. 56 Project Timeline .................................................................................................................... 57 viii LIST OF TABLES Chapter Page Table 1 - Energy Generation Strategies to Improve the Usefulness of Small UAVs .....................2 Table 2 - Comparison of airframes and autopilots among Autonomous soaring projects ..............5 Table 3 -Thermal Model Parameters.......................................................................................... 10 Table 4 - Cooperative Control Logic ......................................................................................... 17 Table 5 - Simulation Parameters ................................................................................................ 19 Table 6 - Noteworthy Attributes of May 8th 2010 Autonomous Soaring Flight ......................... 41 Table 7 - Summary of requirements and results of cooperative soaring experiments .................. 48 ix LIST OF FIGURES Chapter Page Figure 1 - 3 Paragliders Work COOPERATIVELY to Core a Thermal (7) ..................................4 Figure 2 - Simulation Architecture ..............................................................................................8 Figure 3 - Thermal field produced using the NASA thermal model .............................................9 Figure 4 - SBXC speed polar as measured by Dan Edwards ...................................................... 12 Figure 5 - The SBXC, which was modeled in simulation ..........................................................