Powertrain Design for Hand- Launchable Long Endurance Unmanned Aerial Vehicles Stuart Boland Derek Keen 1 Justin Nelson Brian Taylor Nick Wagner Dr. Thomas Bradley 47 th AIAA/ASME/SAE/ASEE JPC
Outline 2 Introduction Motivation Technical Approach Design Structure Matrix Test Case Testing
Introduction 3 The use of Unmanned Aerial Vehicles (UAVs) is widespread. The United States, alone, has exceeded 500,000 flying hours as of January 2008. The most widely used of these MUAVs is the RQ-11 Raven. It can be transported by Humvee and then carried by one person, deployed in approximately 15 minutes, launched by hand and capable of 110 minutes flight endurance.
Introduction 4 Sample of current Miniature UAV designs. Flight Endurance vs. Takeoff Mass
Introduction 5 Design Trade-Offs: Endurance versus Take-Off Requirements Increased endurance increases mass which requires more thrust for hand-launchability. Endurance versus Packability Increased endurance increases mass which increases mass of entire system. Understanding and optimization among these trade-offs may lead to better designs.
Motivation 6 Development of successful back-packable, hand-launchable, long endurance UAVs requires the understanding three competing qualities: 1. Hand-launchability 2. Back-packability 3. Endurability
Motivation 7 Hand Launchability (Prelim Analysis): User can only throw so fast Lower stall velocity leads to much larger wings, but easier launch. Can we overcome the difference in throwing velocity and stall velocity with thrust? Wing Area vs. Stall Velocity for 2.5 kg Aircraft *Using Newton s Laws
Motivation 8 Backpackability (Prelim): Low Weight Soldier Maximum Load = 60 lbs. Fighting Load = 35 lbs. Leaves 25 lbs for UAS Small Form Factor To maintain maneuverability max pack dimensions for height and width must be set. Elbow to Elbow Breadth for 95 th Percentile Male = 50.5 cm Normal Sitting Height for 95 th Percentile Male = 93 cm
Motivation 9 Packing Concepts: Folding Wings Detachable Wings Inflatable Wings Telescoping Wings Plot assumes constant chord length of 30cm.
Motivation 10 Endurability (Prelim): Increase the mass of the batteries on the airplane or increase the cost with better battery technology. We consider the battery to be 50% of the total aircraft mass.
Technical Approach 11 Problem Statement Calculate Endurance Values for MPUAVs Build An Aircraft Meeting Design Specifications Demonstrate Endurance Through Flight and HiL Testing
Technical Approach 12 Design Space: Partial Matrix of Alternatives Attributes Alternative 1 Alternative 2 Alternative 3 Vehicle Conventional Canard Flying Wing Configuration Planform Straight Tapered Elliptical Wing Position High Wing Mid Wing Low Wing Fuselage Tadpole Cylindrical Streamlined Propulsion Tail Configuration Conventional T-Tail V-Tail Energy Storage NiMH Lithium Polymer PEM Fuel Cell Propeller Position Tractor Pusher Structures Materials Wood Composite Combination Process Monocoque Space Frame Landing Gear Fixed Retractable None Decisions made by either qualitative or quantitative analysis.
Technical Approach 13 Contributing Analyses: Aerodynamics CA Hand-Launch CA Propeller CA Motor CA Lithium Polymer Battery CA Performance CA
Technical Approach 14 Contributing Analyses: Aerodynamics CA Hand-Launch CA Propeller CA Motor CA Lithium Polymer Battery CA Performance CA
Technical Approach 15 Hand-Launch Contributing Analysis Equations of Motion Derived By FBD Initial Velocity Determined Experimentally ~8 m/s
Technical Approach 16 Lithium Polymer Battery Contributing Analysis Scalable Static Battery Polarization Linear Model Improved Computational Efficiency
Technical Approach 17 Performance Contributing Analysis Calculates Motor and Propeller Efficiencies at Launch and Cruise To make sure the aircraft is real. (Windmilling, efficiencies > 100%, negative efficiencies) Calculates Launch and Cruise Thrust Error To make sure the aircraft will meet launch and cruise requirements. Calculates Aircraft Endurance
Design Structure Matrix 18
Design Structure Matrix 19 DSM Optimization Methods Darwin Genetic Algorithm (Advanced Design and Optimization Technologies) Multiple near optimal designs Better chance of finding global optimum Objectives Minimize Motor Mass Maximize Endurance Results in Pareto Optimal Trade Study Importance of Motor Mass Or Endurance Used to Select Proper Powertrain.
Design Structure Matrix 20 DSM Optimization Methods Optimization Constraints 0 < Motor Efficiency <.85 0 < Propeller Efficiency <.90-0.01N < Thrust Errors < 0.01N Design Constraints 0 cm < Propeller Diameter 0 cm < Propeller Pitch 0 < Number of Battery Cells
Test Case 21 Wing/Tail Powertrain Payload Autopilot/Remot e Control Control Surface Servo Motors Airframe, Fuselage, Linkages and Wiring Pack
Test Case 22 Preliminary Design Choices Aircraft Mass 2.5 kg Wing Area -.54 m2 Stall Velocity = ~10 m/s Wing Span - 1.8 m Constrained to Pack Dimensions Wing Chord - 30 cm
Test Case 23 Wing and Tail Design XFLR5 Analysis Software aided: Wing and tail configuration Flight behavior prediction Parameters considered: Airfoil choices Size of tail surface Length of tail boom Wing/Tail angles-ofincidence Analysis results validated against hand calculations XFLR5 aircraft analysis software
Test Case 24 Taperless, Straight Wing Ease of manufacture Packability Simplicity Wing Airfoil, HQ 2.5-9 B Balance of Low-drag High-lift Flight behavior Tail Airfoil, NACA 0009 Balance of Low-drag Linear lift properties XFLR5 aircraft analysis software
Test Case 25
Test Case 26 Pareto Optimal Powertrain Design Batteries Motor Propeller Endurance (est.) 4x ThunderPower RC 3S ProLite MS 4000 mah Hacker A40-14L RFM 20 x13 +9 Offset Spinner ~5 Hours
Test Case 27 Fuselage Design Airframe designed around system layout of powertrain and payload. Adjustable center of gravity and multiple battery placement options. Materials chosen for high strength-to-weight ratio. Carbon fiber supports Nylon components Fiberglass-Rohacell sandwich, later replaced with Birch-ply Pro/Engineer used to visualize system layo
Test Case 28
Testing 29 Initial flight tests were completed to determine the baseline endurance of the aircraft in steady level flight conditions. Average wattage, 40W. Not ideal testing conditions. Future testing will be completed with autopilot enabled. These tests were also used to determine hand launchability.
Testing 30 Hardware in the Loop Testing: Hardware in the loop endurance testing was completed to determine the ultimate endurance of the aircraft. One test was conducted and found the ultimate endurance of the aircraft to be 3.2 hours. Schematic and control system causality flowchart for HIL simulation.
Testing 31 Major Sources of Error: Battery Capacity Actual Battery Storage is 11.41 Ah vs. 16 Ah rated capacity. Endurance drops from ~5 hrs to ~3.6 hrs. This equates to a -6% error on actual power consumption. Linear Battery Model A state of charge resolved battery model will provide greater endurance calculation accuracy. Pilot vs. Autopilot Cruise Conditions Steady level flight not necessarily achieved by pilot. The effect of this has not been measured to date.
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33 Preliminary results indicate that optimizing aircraft power plants make significant improvements in aircraft endurance. Future Work: Complete full endurance flight test. Test other powerplant designs from the optimization.
Questions? 34