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Case Studies:Solar Powered AirplanesPhilipp Oettershagen, Autonomous Systems [email protected] Systems Lab 12.12.2016 1

Topics in this case study OverviewHistory and state-of-the-art of solarpowered (unmanned) aircrafts Concept DesignEnergetic modeling for sustainedsolar powered flight*(*Or: How can we reach world-record endurance on/for asmall Unmanned Aerial Vehicle) Flight AutonomyAutonomous flight and Kalmanfiltering approaches for theautonomous tracking of thermalupdraftsAutonomous Systems Lab 12.12.2016 2

Part 1: OverviewHistory and State-of-the-artAutonomous Systems Lab 12.12.2016 3

Why Solar Powered Flight now? MotivationToday, realization of solar airplanes forcontinuous flight is possible efficient and flexible solar cells High energy density batteries Miniaturized sensors and processors Lightweight construction techniquesAutonomous Systems Lab 12.12.2016 4

Possible Solar UAS, May 15th 2008Disaster Scenario / Search and RescueWildfires in California October 2007Early Wildfire DetectionAutonomous Systems LabAgricultural and industrial inspectionAltair/SRHigh-Altitude Long Endurance (HALE) 12.12.2016 5

Working Principle of Solar-Electric AirplanesAutonomous Systems Lab 12.12.2016 6

Introduction – History of Solar Flight Premises of solar aviation with modelairplanes first flight of a solar-powered airplane:4th Nov. 1974, Sunrise I & II (Boucher, US)Wingspan 9.76 mMassSunrise II, 197512.25 kg4480 solar cells 600 W; Max duration: 3 hours In Europe, H. Bruss & F. Militky withSolaris in 1975 Since then, this hobby became „affordable“MikroSol, PiciSol, NanoSol 1995-1998Autonomous Systems LabSolaris, 1976Solar Excel, 1990 12.12.2016 7

Introduction – History of Solar Flight The dream of manned solar flight first attempts : battery charged on the groundwith solar power then flights of some minutesSolar Riser, 1979(Solar One of Fred To (UK) in 1978 and Solar Riserfrom Larry Mauro (US) in 1979) 1st solar manned flight without energy storage:Gossamer Penguin of Dr. MacCready (US) in 1979.Gossamer Penguin, 1980 Next version: Solar Challenger crossed theEnglish channel in 1981Solar Challenger, 1981Autonomous Systems Lab 12.12.2016 8

Introduction – History of Solar Flight The dream of manned solar flightSolair I, 1981 In 1983, Günter Rochelt (D) flies Solair Iduring 5 hours 41 minutes In 1986, Eric Raymond (US) starts buildingSunseeker. In 1990, he crossed the USA in 21solar-powered flights with 121 hours in the airSunseeker, 1990 In 1996, Icare 2 wins the “Berblinger Contest”in Ulm (D). In 2010, SolarImpulse A flies through the night(26h fully sustained flight) In 2015, SolarImpulse B flies for 117h 52min(World Endurance and Range record for solarpowered manned airplanes)Autonomous Systems LabIcare 2, 1996SolarImpulse, 2010 12.12.2016 9

Introduction – Historyof Solar Flight The way to High Altitude LongEndurance (HALE) platforms 1st continuous flight: Alan Cocconi ofAcPropulsion built SoLong in 2005 Use of Solar Power and Thermals22nd of April 2005 : 24 hours 11 min3rd of June 2005 : 48 hours 16 minSolong, 2005 Qinetiq (UK) built Zephyr in 2005 December 2005 : 6 hours at 7’925 mJuly 2006 : 18 hours flight(7 during night)Sept 2007 : 53 hoursAugust 2008 : 83 hoursJuly 2010: 336 hours (world flight endurance record)Zephyr, 2005Autonomous Systems Lab 12.12.2016 11

High Altitude Long Endurance platforms todayAirbus - ZephyrFacebook - AquilaGoogle - Titan22.86 m42 m50 m50 kg400 kg160 kg19.8 km18-28 km19 kmAutonomous Systems Lab 12.12.2016 12

Part 2: Concept DesignEnergetic modeling for sustained solar powered flightAutonomous Systems Lab 12.12.2016 13

Solar-Electric Airplane Conceptual DesignVarious missions High Altitude LongEndurance(HALE) Low AtmosphereSurveillance Different degreesof autonomy Mars mission?Various payloadrequirements Sensors(cameras) Communicationlinks Processing power Navigation system Human?Choice of DesignVariables Wingspan Aspect Ratio Battery SizeHow do I do this?What performance can I expect?Autonomous Systems Lab 12.12.2016 14

Solar-powered UAV Conceptual Design: A ToolDesign variables:Wingspan, aspect ratio,battery massTechnologicalparameters:Efficiencies, massmodels, rib or shell wingPayloadMass, power consumptionCore Module:AerodynamicsPower Train Mass EstimationStructure DimensioningMassesEnvironmentAltitude, latitude,longitude, day, .PolarsRun (constrained)optimizationPerformance EvaluationSimulation of the DayMode of Operation:Allow variable altitudeyes/noEndurance /Excess Time /Charge marginAutonomous Systems LabMax. Altitude forContinuous Flight[8]: S. Leutenegger, M. Jabas, and R. Y. Siegwart.Solar Airplane Conceptual Design andPerformance Estimation. Journal of Intelligent andRobotic Systems, Vol. 61, No. 1-4, pp. 545-561 12.12.2016 15

Basic System Modeling (1/2) Forward-integration of state equations: Power modelingI I (day,t,lat,h)ISolar irradiance [W/m²]AsmSolar module area [m²]ηsm, ηmppt Solar module and maximum power pointtracker efficiency [-]Pav, Ppld Avionics and payload power [W]Autonomous Systems LabηpropPropulsion system efficiencymtotTotal airplane mass 12.12.2016 17

Basic System Modeling (2/2)To derive the level flight power (constant altitude flight), we combinewithvAirspeed [m/s]AwingWing area [m²]CD, CL Drag / Lift coefficients [-]ρLocal air density [kg/m³]and minimize the resulting expression w.r.t. the airspeed to yieldCD and CL are functions of the airspeed v! They areretrieved from airplane and airfoil analysis tools such asXFOIL or XFLR5.Example (see image): AtlantikSolar UAV, MH139 airfoil, mtot 6.9kg,Awing 1.7m², vopt 7.6m/s, Plevel 21W.Autonomous Systems Lab 12.12.2016 18

Performance MetricsEbatBattery energy [J]SoCBattery state of charge [%]PoutnomNominal required output power [W]If perpetual flight is not possible, the main performance metric is the maximum endurance Tend.If perpetual flight is possible, we define:In the conceptual design phase, we optimize both Texc and Tcm togenerate sufficient safety margins for perpetual flight!Autonomous Systems Lab 12.12.2016 19

Conceptual Design Results Low-altitudeperpetual flight(700m AMSL) Currenttechnology Aspect ratio 12 Minimal payload:0.6kg, 7W Latitude37.34 N June 21 Clear skyAutonomous Systems Lab 12.12.2016 24

Example: SolarPowered Airliner? Payload 100 passengers, 12000 kg Speed: 600 km/h Height: 12 km: 0.31 kg/m3 Wing area and mass for AR 10:b22mgCL 0.5 A 2AR V CLm m pld m propulsion mstruct m pld b 0.043 m 3.1AR 0.25 kg m 13 t (unrealistically light),b 24 m, A 57 m2 Power for level flight / Drag:Assume glide ratio 1:30 CD CL/30Plevel 2AC DV 3 680 kWIt is – unfortunately – farfrom being realistic Solar Power Irradiance: max. 1.4 kW/m2Autonomous Systems Lab 12.12.2016 25

Solar-powered UAV Design Example AtlantikSolar UAVWingspanMassNominal cruise speedMinimum enduranceaRecord enduranceMax. solar powerPower consumption 5.65 m6.9 kg10 m/s13 hrs81.5 hrs280 W43 Wa – full battery with no solar chargingFor student projects, please contact us!Autonomous Systems Lab(e.g. [email protected]) 12.12.2016 29

PerceptionAvionicsAutopilot and SensorsCommunicationSensorpodExternal camerasPixhawk PX4AutopilotPrimary: 3DR radioLong-Range: IridiumSATCOMIMU: ADIS16448GoPro Hero 3 silverAirspeed Sensing:Sensirion SDP600Radio control:SpektrumGPS: U-Blox Lea-6HuBloxFirst person viewgogglesRobust EKF-basedState estimationLeutenegger, S.; Melzer, A.; Alexis, K.; Siegwart, R.,"Robust state estimation for small unmannedairplanes," in Control Applications (CCA), 2014Autonomous Systems LabOptical cameras:Aptina MT9V034,IDS UI-3251LEThermal camera:FLIR Tau 2Sony HDR AS100VSimultaneous Localization and Mapping (SLAM)Human detectionAgricultural inspection 12.12.2016 30

Sensorpod: Sensor and Processing UnitVisual-inertial SLAM sensor Autonomous Systems LabJanosch Nikolic, Joern Rehder, Michael Burri, Pascal Gohl,Stefan Leutenegger, Paul T Furgale, Roland Siegwart,A synchronized visual-inertial sensor system with FPGApre-processing for accurate real-time SLAM, Robotics andAutomation (ICRA), 2014 IEEE International Conference on,pp.431–437, 2014 12.12.2016 31

Flight-endurance record: 81h flight (14.07.15) Conditions Excellent irradiance Significant thermalsduring the day Achievements Duration:81h23mDistance:2316kmAv. airspeed: 8.6 m/sP mean:43WSoCmin:39%World record in flightendurance for allaircrafts with mtot 50kgAutonomous Systems Lab Continuous flight proven to befeasible with good energetic marginsand without using thermals orpotential energy storage 12.12.2016 32

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Part 3: Flight AutonomyAutonomous flight and recursive filtering approaches for the autonomoustracking of thermal updraftsAutonomous Systems Lab 12.12.2016 39

Flight Autonomy:Example: Autonomous Thermal Updraft TrackingColumn ofrising airAutonomous Systems Lab 12.12.2016 40

Flight Autonomy:Example: Autonomous Thermal Updraft Tracking 𝑀𝑎𝑥. 𝑢𝑝𝑑𝑟𝑎𝑓𝑡 𝑖𝑢𝑠𝑋 𝑥𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑛𝑜𝑟𝑡ℎ 𝑜𝑓 𝐴/𝐶𝑦𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑒𝑎𝑠𝑡 𝑜𝑓 𝐴/𝐶00𝑋𝑘 1 𝑓 𝑋𝑘 𝑋𝑘 𝑣𝑤𝑖𝑛𝑑,𝑛𝑜𝑟𝑡ℎ Δℎൗ𝑣𝑐 𝑣𝑤𝑖𝑛𝑑,𝑒𝑎𝑠𝑡 Δℎൗ𝑣𝑐𝑧1 𝑤 𝑊, 𝑅, 𝑥, 𝑦 𝑊 Autonomous Systems Lab𝑥 2 𝑦 2 𝑒 𝑅2vwind 12.12.2016 41

Flight Autonomy:Example: Autonomous Thermal Updraft Tracking2𝑐 𝑟 𝑊 𝑟 2𝑧2 𝑒 𝑅 sin 𝜁 cos 𝜙𝑅2𝜙 Roll angle. 𝜓 Yaw Angle. 𝜁 Direction of. thermal center𝑟 𝑥2 𝑦2𝑠𝑖𝑛𝜁 𝜙𝜓 0 cos 𝜓 𝑦 sin 𝜓 𝑥𝑟𝜁 90 Autonomous Systems Lab 12.12.2016 42

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References[1] B.W. McCormick. Aerodynamics, Aeronautics and Flight Mechanics – 2nd Edition. John Wiley &Sons, 1995[2] J. Wildi. Grundlagen der Flugtechnik / Ausgewählte Kapitel der Flugtechnik. Lecture Notes ETHZurich[3] B. Etkin. Dynamics of Atmospheric Flight. Dover Publications, 2005[4] G. J. J. Ducard. Fault-Tolerant Flight Control and Guidance Systems for a Small Unmanned AerialVehicle. PhD Thesis ETH Zurich No. 17505, 2007[5] R.W. Beard and T.W. McLain. Small Unmanned Aircraft: Theory and Practice. Princeton UniversityPress, 2012. ISBN: 9780691149219.[6] A. Noth. Design of Solar Powered Airplanes for Continuous Flight. PhD Thesis ETH Zurich No.18010, 2008[7] H. Tennekes. The Simple Science of Flight. From Insects to Jumbo Jets. Revised and ExpandedEdition, 2009. MIT Press. Paperback ISBN 978-0-262-51313-5[8] S. Leutenegger, M. Jabas, and R. Y. Siegwart. Solar Airplane Conceptual Design and PerformanceEstimation. Journal of Intelligent and Robotic Systems, Vol. 61, No. 1-4, pp. 545-561, DOI:10.1007/s10846-010-9484-xAutonomous Systems Lab 12.12.2016 44

Thanks for your attention! ous Systems Lab 12.12.2016 45

Introduction –History of Solar Flight Wingspan 9.76 m Sunrise II, 1975 Mass 12.25 kg 4480 solar cells 600 W; Max duration: 3 hours Solaris, 1976 MikroSol, PiciSol, NanoSol 1995-1998 Solar Excel, 1990 12.12.2016 7