Case Studies: Design of Solar Powered Airplanes

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1 Case Studies: Design of Solar Powered Airplanes Philipp Oettershagen, Fixed Wing UAS: Control and Fuel Case Studies

2 Introduction: Why Solar Powered Flight? Motivations Today, realization of Solar Airplanes for continuous flight is possible efficient and flexible solar cells (1 st 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 UAVs Fixed Wing UAS: Control and Fuel Case Studies

3 Working Principle of Solar-Electric Airplanes Fixed Wing UAS: Control and Fuel Case Studies

4 Possible Solar UAS Applications Yingxiu, May 15th 2008 Disaster Scenario / Search and Rescue Agricultural and industrial inspection Wildfires in California October 2007 Early Wildfire Detection Altair/SR High-Altitude Long Endurance (HALE) Fixed Wing UAS: Control and Fuel Case Studies

5 Introduction History of Solar Flight Premises of solar aviation with model airplanes first flight of a solar-powered airplane: 4 th Nov. 1974, Sunrise I & II (Boucher, US) Wingspan 9.76 m Mass kg Sunrise II, solar cells 600 W; Max duration: 3 hours In Europe, H. Bruss & F. Militky with Solaris in 1975 Since then, this hobby became affordable Solaris, 1976 MikroSol, PiciSol, NanoSol Solar Excel, 1990 Fixed Wing UAS: Control and Fuel Case Studies

6 Introduction History of Solar Flight The dream of manned solar flight first attempts : battery charged on the ground with solar power then flights of some minutes (Solar One of Fred To (UK) in 1978 and Solar Riser from Larry Mauro (US) in 1979) 1 st solar manned flight without energy storage: Gossamer Penguin of Dr. MacCready (US) in Solar Riser, 1979 Gossamer Penguin, 1980 Next version: Solar Challenger crossed the English channel in 1981 Solar Challenger, 1981 Fixed Wing UAS: Control and Fuel Case Studies

7 Introduction History of Solar Flight The dream of manned solar flight In 1983, Günter Rochelt (D) flies Solair I during 5 hours 41 minutes In 1986, Eric Raymond (US) starts building Sunseeker. In 1990, he crossed the USA in 21 solar-powered flights with 121 hours in the air 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) Solair I, 1981 Sunseeker, 1990 Icare 2, 1996 Solarimpulse, 2010 Fixed Wing UAS: Control and Fuel Case Studies

8 Introduction History of Solar Flight The way to High Altitude Long Endurance (HALE) platforms 1 st continuous flight: Alan Cocconi of AcPropulsion built SoLong in 2005 Use of Solar Power and Thermals 22nd of April 2005 : 24 hours 11 min 3rd of June 2005 : 48 hours 16 min Solong, 2005 Qinetiq (UK) built Zephyr in 2005 December 2005 : 6 hours at m July 2006 : 18 hours flight (7 during night) Sept 2007 : 53 hours August 2008 : 83 hours July 2010: 336 hours (world flight endurance record) Zephyr, 2005 Fixed Wing UAS: Control and Fuel Case Studies

9 High Altitude Long Endurance platforms today Airbus - Zephyr Facebook - Aquila Google - Titan m 42 m 50 m 50 kg 400 kg 160 kg 19.8 km km 19 km Fixed Wing UAS: Basics of Aerodynamics 23

10 Solar-Electric Airplane Conceptual Design Various missions High Altitude Long Endurance (HALE) Low Atmosphere Surveillance Different degrees of autonomy Mars mission? Various payload requirements Sensors (cameras) Communication links Processing power Navigation system Human? Choice of Design Variables Wingspan Aspect Ratio Battery Size How do I do this? What performance can I expect? Fixed Wing UAS: Control and Fuel Case Studies

11 Solar-powered UAV Conceptual Design: A Tool Design variables: Wingspan, aspect ratio, battery mass Design variables Technological parameters (inputs) User parameters (inputs) Performance metrics (outputs) Technological parameters: Efficiencies, mass models, rib or shell wing Payload Mass, power consumption Environment Altitude, latitude, longitude, day,... Mode of Operation: Allow variable altitude yes/no Core Module: Aerodynamics Power Train Mass Estimation Structure Dimensioning Masses Polars Performance Evaluation Simulation of the Day Run (constrained) optimization Endurance / Excess Time / Charge margin Max. Altitude for Continuous Flight [8]: S. Leutenegger, M. Jabas, and R. Y. Siegwart. Solar Airplane Conceptual Design and Performance Estimation. Journal of Intelligent and Robotic Systems, Vol. 61, No. 1-4, pp Fixed Wing UAS: Control and Fuel Case Studies

12 Performance Metrics (1/2) Case 1: Perpetual flight not possible Performance metric: T end (Endurance). T end can be >24h (even though continuous flight is not possible) Power Required Power Endurance E_bat Solar Power Case 2: Perpetual flight possible Performance metrics: Excess time T exc Minimum state of charge Charge margin T cm Power 12 h 24 h Solar Power Excess time Time Required Power E_bat 12 h 24 h Fixed Wing UAS: Control and Fuel Case Studies Time

13 Performance Metrics (2/2) If perpetual flight is possible, we define: E bat Battery energy [J] SoC Battery state of charge [%] P out nom Nominal required output power [W] In the conceptual design phase, we optimize both T exc and T cm to generate sufficient safety margins for perpetual flight! Fixed Wing UAS: Basics of Aerodynamics 27

14 Basic System Modeling (1/2) Forward-integration of state equations: Power modeling I = I (day,t,lat,h) I A sm Solar irradiance [W/m²] Solar module area [m²] η sm, η mppt Solar module and maximum power point tracker efficiency [-] P av, P pld Avionics and payload power [W] η prop m tot Propulsion system efficiency Total airplane mass Fixed Wing UAS: Basics of Aerodynamics 28

15 Basic System Modeling (2/2) To derive the level flight power (constant altitude flight), we combine with v Airspeed [m/s] A wing Wing area [m²] C D, C L Drag / Lift coefficients [-] ρ Local air density [kg/m³] and minimize the resulting expression w.r.t. the airspeed to yield C D and C L are functions of the airspeed v! They are retrieved from airplane and airfoil analysis tools such as XFOIL or XFLR5. Example (see image): AtlantikSolar UAV, MH139 airfoil, m tot =6.9kg, A wing =1.7m², v opt =7.6m/s, P level =21W Fixed Wing UAS: Basics of Aerodynamics 29

16 Mass Models (1/2) Scaling of mass seems easy at first glance [6,7]: 3 W L mg b S b W / S 2 b W / S k W [6] (Assumption: Geometric similarity) Fixed Wing Aircraft

17 Mass Models (2/2) Fixed Wing UAS: Control and Fuel Case Studies

18 Improvements to the Mass Models Structure mass is depending on: Payload (mass) Payload location/distribution Wing geometry (also airfoil!) Structure concept Load cases Fixed Wing UAS: Control and Fuel Case Studies

19 Example: Solar Powered Airliner? Payload 100 passengers, kg Speed: 600 km/h Height: 12 km: = 0.31 kg/m 3 Wing area and mass for AR=10: b AR m 2mg V CL m 2 CL 0.5 A 2 m m m pld pld propulsion b m 3.1 AR struct 0.25 kg m 13 t (unrealistically light), b 24 m, A 57 m 2 Power for level flight / Drag: Assume glide ratio 1:30 C D =C L /30 P level AC V 3 D 680 kw 2 Solar Power Irradiance: max. 1.4 kw/m 2 It is unfortunately far from being realistic Fixed Wing UAS: Control and Fuel Case Studies

20 Conceptual Design Results (1/1) Low-altitude perpetual flight (700m AMSL) Current technology Aspect ratio 12 Minimal payload: 0.6kg, 7W Latitude N June 21 Skyclear Fixed Wing UAS: Control and Fuel Case Studies

21 Solar-powered UAV Design Example Hand-launchable and rapidly deployable Fully autonomous, minimal supervisory requirements Versatile sensor payload (e.g. AtlantikSolar UAV Wingspan Mass Nominal cruise speed Minimum endurance a Record endurance Max. solar power Power consumption a full battery with no solar charging For student projects, please contact us! 5.65 m 6.9 kg 10 m/s 13 hrs 81.5 hrs 280 W 43 W

22 Flight-endurance record: 81h flight ( ) Conditions Excellent irradiance Significant thermals during the day Achievements Duration: Distance: 81h23m 2316km Av. airspeed: 8.6 m/s P_mean: 43W+15W SoC min : 39% World record in flight endurance for all aircrafts with m tot <50kg Continuous flight proven to be feasible with good energetic margins and without using thermals or potential energy storage Fixed Wing UAS: Control and Fuel Case Studies

23 Technical Progress and Scaling Considerations Energy Generation and Storage Absolute Characteristics SkySailor (2008) SenseSoar (2012) AtlantikSolar (2014) m tot 2.5kg 5.1kg 7.0kg Wing span 3.2m 3.1m 5.6m Battery mass 1.05kg 1.9kg 2.9kg Aspect ratio P max solar 90W 140W 280W E bat 252Wh 460Wh 710Wh Slow but steady progress on PV and battery technology! But sensors and avionics have minituarized, too. Technological Progress SkySailor (2008) SenseSoar (2012) AtlantikSolar (2014) η SolarModule 17% 19% 23% e bat 240Wh/kg (Li-Ion) 245Wh/kg (Li-Ion) 255Wh/kg (Li-Ion) Fixed Wing UAS: Control and Fuel Case Studies

24 Avionics Perception Communication Autopilot and Sensors Sensorpod External cameras Primary: 3DR radio Pixhawk PX4 Autopilot Long-Range: Iridium SATCOM IMU: ADIS16448 GoPro Hero 3 silver Radio control: Spektrum Airspeed Sensing: Sensirion SDP600 Optical cameras: Aptina MT9V034, IDS UI-3251LE First person view goggles GPS: U-Blox Lea-6H ublox Thermal camera: FLIR Tau 2 Sony HDR AS100V APPLICATIONS Robust EKF-based State estimation Leutenegger, S.; Melzer, A.; Alexis, K.; Siegwart, R., "Robust state estimation for small unmanned airplanes," in Control Applications (CCA), 2014 Simultaneous Localization and Mapping (SLAM) Human detection Agricultural inspection

25 Sensorpod: Sensor and Processing Unit Visual-inertial SLAM sensor Developed at ETH Zurich FPGA board for visual-inertial odometry Hardware synchronized IMU and camera data Up to four cameras Janosch Nikolic, Joern Rehder, Michael Burri, Pascal Gohl, Stefan Leutenegger, Paul T Furgale, Roland Siegwart, A synchronized visual-inertial sensor system with FPGA pre-processing for accurate real-time SLAM, Robotics and Automation (ICRA), 2014 IEEE International Conference on, pp , 2014

26 Fixed Wing UAS: Control and Fuel Case Studies

27 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 ETH Zurich [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 Aerial Vehicle. PhD Thesis ETH Zurich No , 2007 [5] R.W. Beard and T.W. McLain. Small Unmanned Aircraft: Theory and Practice. Princeton University Press, ISBN: [6] A. Noth. Design of Solar Powered Airplanes for Continuous Flight. PhD Thesis ETH Zurich No , 2008 [7] H. Tennekes. The Simple Science of Flight. From Insects to Jumbo Jets. Revised and Expanded Edition, MIT Press. Paperback ISBN [8] S. Leutenegger, M. Jabas, and R. Y. Siegwart. Solar Airplane Conceptual Design and Performance Estimation. Journal of Intelligent and Robotic Systems, Vol. 61, No. 1-4, pp , DOI: /s x Fixed Wing UAS: Control and Fuel Case Studies

28 Thanks for your attention! Questions? Fixed Wing UAS: Control and Fuel Case Studies