University of Cincinnati Aerospace Engineering and Engineering Mechanics Masters of Science Thesis Transition of Quadcopter Box-Wing UAV between Cruise and VTOL Modes A thesis submitted to the Graduate school, University of Cincinnati in partial fulfillment of requirements for the degree in Master of Science in Aerospace Engineering and Engineering of the College of Engineering and Applied Sciences by Gaurang Gupta Committee Chair: Shaaban Abdallah, Ph.D August 2, 2018 Abstract The aim of this thesis is to present an algorithm for autonomous control of a quadcopter Unmanned Aerial Vehicle, (UAV), equipped with a box-wing, which is capable of transition between hover and forward flight mode. In particular, this re- search work describes position and attitude control in such a quadcopter equipped with a wing. UAVs perform missions which require efficient operation in both hover and forward flight. This project discusses the incorporation of these two different flight modes in one single aircraft. The quadcopter UAV equipped with a box-wing is a structural advancement of traditional quadcopter and it provides improved cruising efficiency of the aircraft during flight. In conventional quadcopter, the two diagonally opposite propellers rotate in clockwise direction and other two propellers rotate in counter clockwise direction to balance the effective yawing moment of the system. The variation in rotational speeds of the four propellers, is utilized for maneuvering and achieving the desired transition from hover to cruise by pitching the aircraft by almost 90 degree or vice-versa. The proposed UAV is equipped with a box-wing and quadcopter in `X' config- uration, with gross takeoff weight of around 2 kg. The aerodynamic characteristics of the box-wing are estimated through a series of Computational Fluid Dynamics (CFD) simulations. A new PID control strategy is developed using the lineariz- ing technique of non-linear governing equations of motion, which works towards achieving stable transition between hover and forward flight modes with as less oscillations as possible. MATLAB simulations of these maneuvers are performed which have successfully shown the ability to achieve desired attitude along with performing hover, transition and roll maneuvers. A model is constructed to test and validate the newly developed control strategy and its ability to achieve desired altitude and perform various maneuvers as listed above. The box-wing is fabricated out of foam using hot-wire cutting method and iii the quadcopter frame sits right on the top of the leading edges of the upper and the lover wing. The control hardware is placed in the center of the frame, which is con- sidered to be the body center and is located not far away from the center of mass of the entire system. The entire control strategy is developed around this body center. Overall, the quadcopter equipped with a box-wing, has proven to be an efficient and effective multi-role vehicle. This vehicle type is valuable from a commercial standpoint of view as it offers high maneuverability with small payload delivery capabilities. iv Acknowledgement I would like to thank all my friends an colleges who helped and supported me throughout this research. I would like to specially thank Siddharth Sridhar for helping me quadcopter dynamics and hardware; Bryan Brown for helping with hardware as well; Karthick Vigneshwar for helping me with CFD simulation; Gaurav Patil for helping me with 3D printing; Robert Ogden for helping me with super-computer resources for CFD simulations and lastly Curtis Fox for helping me with all tools and resources for fabricating the wing. Thank you all. vi Contents Abstract iii Acknowledgement vi List of figures xi List of tables xii 1 Introduction 1 1.1 Motivation .................................1 1.2 Literature survey .............................2 1.3 Vehicle configuration ...........................6 1.3.1 Fixed wing UAV . .6 1.3.2 Rotary wing UAV . .7 1.3.3 Flapping wing UAV . .7 1.3.4 Hybrid vehicle configuration . .8 1.3.5 Tilt-wing vehicle . .8 1.3.6 Tilt-rotor vehicles . .9 1.3.7 Fan-in-wing vehicle . .9 1.3.8 Tail-sitter vehicle . 10 2 Preliminary design 13 2.1 Design requirements ........................... 13 2.2 Objective .................................. 13 2.3 Required lift and thrust estimate for the aircraft ........ 14 3 Box-wing design 17 3.1 Aerodynamics ............................... 18 3.1.1 Lifting area sizing . 18 3.1.2 Stagger and gap sizing . 19 3.1.3 Airfoil selection . 21 vii 3.2 CAD model ................................. 23 4 CFD simulation 25 4.1 Meshing and grid independency ................... 26 4.2 CFD solver selection ........................... 29 5 Dynamic Model 33 5.1 Frame of reference ............................ 33 5.2 Inertial properties ............................. 36 5.3 Quaternion formulation ......................... 37 5.4 Angle of attack and heading angle .................. 40 5.5 Aerodynamic forces and moments .................. 41 5.6 Governing equations of motion .................... 44 6 Linearization of governing equations of motion 47 6.1 Longitudinal Motion ........................... 47 6.1.1 Summary of linearized longitudinal equations of motion . 50 6.2 Lateral Motion ............................... 51 6.2.1 Summary of linearized lateral equations of motion . 53 6.3 Aerodynamic derivatives ........................ 54 6.3.1 Summary of linearized partial aerodynamic derivatives . 56 6.4 Kinematics ................................. 57 6.5 Linearized governing equations of motion ............. 59 7 Control laws 61 7.1 Position error law ............................. 61 7.2 Attitude error law ............................. 63 7.3 Motor input ................................. 64 8 Simulations and results 67 8.1 Hover simulations ............................. 67 viii 8.2 Transition along with roll maneuver simulations ......... 68 8.3 Summary .................................. 74 9 Prototype 79 10 Conclusion 85 11 Future work 87 11.1 CFD result validation .......................... 87 11.2 Strength analysis and fabrication of box-wing .......... 87 11.3 Dynamic model of box-wing ...................... 87 11.4 Controller development ......................... 87 11.5 Flight simulations ............................. 88 References 89 ix List of Figures 1 Harrier with VTOL capability . .3 2 F-35 with VTOL capability . .3 3 Eagle - Eye . .5 4 Skytote . .5 5 Google: Project Wing . .5 6 Black Widow . .6 7 Dragonfly . .8 8 Box-wing . 18 9 Box-wing . 19 10 Cm vs. alpha curve for MH-83 airfoil . 22 11 MH-83 airfoil . 23 12 Bell 540 (modified NACA 0012) airfoil . 23 13 CAD model of box-wing . 24 14 Fluid domain . 27 15 Far field pressure variation . 27 16 Mesh density around airfoil . 28 17 Combined Cl vs. alpha for upper and lower wing section of box wing . 31 18 Combined Cd for entire box-wing . 32 19 Combined Cm vs. alpha for upper and lower wing section of box wing . 32 20 Combined Cm vs. alpha for upper and lower wing section of box wing . 33 21 Euler angle rotation sequence . 34 22 Angle of attack as defined in body frame . 40 23 Heading angle as defined in body frame . 41 24 Aerodynamic forces, moments and mean aerodynamic center (MAC) rep- resentation . 44 25 Quadcopter motor forces and moments . 45 26 Hover: Position vs. Time . 69 27 Hover: Velocity vs. Time . 70 x 28 Hover: Euler angles vs. Time . 71 29 Hover: Angular velocity vs. Time . 72 30 Transition - Roll: Position vs. Time . 75 31 Transition - Roll: Velocity vs. Time . 76 32 Transition - Roll: Euler angles vs. Time . 77 33 Transition - Roll: Angular velocity vs. Time . 78 34 Prototype of proposed model . 79 35 Airfoil section cut . 80 36 Joint flushing cut for side and lower wing . 80 37 Box-wing . 80 38 Mount . 81 39 Quadcopter secured to box-wing . 81 40 Quadcopter frame . 82 41 Pixhawk V2 flight controller . 82 42 Futaba R617FS 2:4GHz receiver . 82 43 NTM 1350kv motor . 83 44 Afro 30A ESC . 83 45 9 x 4.7 propeller . 83 46 5200mAh Turnigy Graphene Li-Po battery . 84 xi List of Tables 1 Initial weight estimate of aircraft components . 15 2 Final weight estimate of aircraft components . 37 xii 1 Introduction 1.1 Motivation UAVs can perform various missions such as surveillance, patrolling, targeting, bio-chemical sensing, environment mapping, search and rescue, \over the hill" or \around the corner" reconnaissance, agricultural observation, wildlife protection, traffic monitoring, medical supply, consumer package delivery, fire-fighting and other tasks that may be hazardous and inconvenient for human involvement. Proving their usefulness in military and civil application for several decades, there still lies a prominent scope of improvement and innovation, in the design and working of UAVs with the ever-changing mission require- ments. There are various types and subsets of UAVs, each being designed for its own specific operational objective. Each of these different configurations have their own sets of advantages and disadvantages depending on the design and the kind of mission they are being used in. Many missions require multiple flight modes like vertically taking-off or landing, hov- ering in one place and cursing to long distances to supply payload, etc. Vertical take-off and landing (VTOL) aircraft and fixed-wing aircraft have their advantages and disadvan- tages. Multi-rotor aircraft can take off and land vertically, but they cannot fly forward with high speed carrying large payloads. Hovering for several minutes at a given location and in one position is the most important