Case Studies: Design Of Solar Powered Airplanes

Case Studies:Design of Solar Powered AirplanesPhilipp Oettershagen, Autonomous Systems Labphilipp.oettershagen@mavt.ethz.chAutonomous Systems LabFixed Wing UAS: Control and Fuel Case Studies 23.11.2015 14

Introduction: Why Solar Powered Flight? MotivationsToday, realization of Solar Airplanes for continuous flight is possible efficient and flexible solar cells (1st solar cell in 1954) High energy density batteries Miniaturized MEMS and CMOS sensors Small and powerful processors Lightweight construction techniques Goals Study the feasibility of solar powered sustained flight Develop a conceptual design methodology Provide overview and design examples of fixed-wing UAVsAutonomous Systems LabFixed Wing UAS: Control and Fuel Case Studies 24.11.2015 15

Working Principle of Solar-Electric AirplanesAutonomous Systems LabFixed Wing UAS: Control and Fuel Case Studies 24.11.2015 16

Possible Solar UAS Applicationswww.telegraph.co.ukYingxiu, May 15th 2008Disaster Scenario / Search and RescueWildfires in California October 2007Early Wildfire DetectionAutonomous Systems LabAgricultural and industrial inspectionAltair/SRHigh-Altitude Long Endurance (HALE)Fixed Wing UAS: Control and Fuel Case Studies 23.11.2015 17

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“Solaris, 1976MikroSol, PiciSol, NanoSol 1995-1998Autonomous Systems LabSolar Excel, 1990Fixed Wing UAS: Control and Fuel Case Studies 23.11.2015 18

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 LabFixed Wing UAS: Control and Fuel Case Studies 23.11.2015 19

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, 2010Fixed Wing UAS: Control and Fuel Case Studies 23.11.2015 20

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 LabFixed Wing UAS: Control and Fuel Case Studies 23.11.2015 22

High Altitude Long Endurance platforms todayAirbus - ZephyrFacebook - AquilaGoogle - Titan22.86 m42 m50 m50 kg400 kg160 kg19.8 km18-28 km19 kmAutonomous Systems LabFixed Wing UAS: Basics of Aerodynamics 23.11.2015 23

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 LabFixed Wing UAS: Control and Fuel Case Studies 23.11.2015 24

Solar-powered UAV Conceptual Design: A ToolDesign variables:Wingspan, aspect ratio,battery massTechnologicalparameters:Efficiencies, massmodels, rib or shell wingPayloadMass, power consumptionDesign variablesTechnological parameters (inputs)User parameters (inputs)Performance metrics (outputs)Core 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. 545-561Fixed Wing UAS: Control and Fuel Case Studies 23.11.2015 25

Performance Metrics (1/2)Case 1: Perpetual flight not possiblePerformance metric: Tend (Endurance). Tend can be 24h (even though continuousflight is not possible)PowerEnduranceRequiredPowerE batSolarPowerCase 2: Perpetual flight possiblePerformance metrics: Excess time Texc Minimum state of charge Charge margin Tcm12 hPowerSolarPowerRequiredPowerExcesstimeE bat12 hAutonomous Systems Lab24 h Time24 hFixed Wing UAS: Control and Fuel Case Studies Time23.11.2015 26

Performance Metrics (2/2)EbatIf perpetual flight is possible, we define:Battery energy [J]SoCPoutnomBattery state of charge [%]Nominal required output power [W]In the conceptual design phase, we optimize both Texc and Tcm togenerate sufficient safety margins for perpetual flight!Autonomous Systems LabFixed Wing UAS: Basics of Aerodynamics 23.11.2015 27

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 massFixed Wing UAS: Basics of Aerodynamics 23.11.2015 28

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 LabFixed Wing UAS: Basics of Aerodynamics 23.11.2015 29

Mass Models (1/2) Scaling of mass seemseasy at first glance [6,7]:W L mg b3S b2W /S bW / S k1 W13[6](Assumption: Geometric similarity)Autonomous Systems LabFixed Wing Aircraft

Mass Models (2/2)Autonomous Systems LabFixed Wing UAS: Control and Fuel Case Studies 23.11.2015 32

Improvements to theMass Models Structure mass isdepending on: Payload (mass)Payload location/distributionWing geometry (also airfoil!)Structure conceptLoad casesAutonomous Systems LabFixed Wing UAS: Control and Fuel Case Studies 23.11.2015 33

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 0.25kg 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 LabFixed Wing UAS: Control and Fuel Case Studies 23.11.2015 34

Conceptual Design Results (1/1) Low-altitudeperpetual flight(700m AMSL) Currenttechnology Aspect ratio 12 Minimal payload:0.6kg, 7W Latitude37.34 N June 21 SkyclearAutonomous Systems LabFixed Wing UAS: Control and Fuel Case Studies 23.11.2015 36

Solar-powered UAV Design Example Hand-launchable and rapidlydeployable Fully autonomous, minimalsupervisory requirements Versatile sensor payloadAtlantikSolar UAVWingspanMassNominal cruise speedMinimum enduranceaRecord enduranceMax. solar powerPower consumption5.65 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. philipp.oettershagen@mavt.ethz.ch)

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: 43W 15WSoCmin: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 storageFixed Wing UAS: Control and Fuel Case Studies 24.11.2015 40

Technical Progress and Scaling ConsiderationsEnergy Generation and StorageAbsoluteCharacteristicsmtotWing spanBattery massAspect AtlantikSolar(2014)23%255Wh/kg(Li-Ion)Autonomous Systems LabSlow but steadyprogress on PV andbattery technology!But sensors andavionics haveminituarized, too.Fixed Wing UAS: Control and Fuel Case Studies 24.11.2015 41

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 estimationAPPLICATIONSLeutenegger, 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

Sensorpod: Sensor and Processing UnitVisual-inertial SLAM sensor Autonomous Systems LabDeveloped at ETH ZurichFPGA board for visual-inertial odometryHardware synchronized IMU andcamera dataUp to four camerasJanosch 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

Autonomous Systems LabFixed Wing UAS: Control and Fuel Case Studies 23.11.2015 48

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 LabFixed Wing UAS: Control and Fuel Case Studies 23.11.2015 49

Thanks for your attention! Questions?Autonomous Systems LabFixed Wing UAS: Control and Fuel Case Studies 23.11.2015 50

first flight of a solar-powered airplane: th4 Nov. 1974, Sunrise I & II (Boucher, US) In Europe, H. Bruss & F. Militky with Solaris in 1975 Since then, this hobby became „affordable“ 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