Solar Based Propulsion System UAV Conceptual Design ( * )

Solar Based Propulsion System UAV Conceptual Design ( * ) Avi Ayele*, Ohad Gur, and Aviv Rosen* *Technion Israel Institute of Technology IAI Israel Aerospace Industries (*) Ayele A., Gur O., Rosen A., "Conceptual MDO of solar powered UAV," 53 rd Israel Annual Conference on Aerospace Sciences, March 6-7, 213, Israel 1

Ragone Chart Curtsey of Lidor A., Weihs D., Sher E. 1.E+9 1.E+8 Ragone Chart 1.E+7 Carbon Nano Tubes Specific Power [W/kg] 1.E+6 1.E+5 1.E+4 1.E+3 1.E+2 1.E+1 1.E+ Metal Spring Pneumatics Shape Memory Alloy Flywheel Phase Change Materials Li-Ion Battery Fuel Cell Internal Combustion Engine Solar Panels Radioisotope Thermoelectric Generator 1.E-1 Synthetic Muscle 1.E-2 1.E-2 1.E-1 1.E+ 1.E+1 1.E+2 1.E+3 1.E+4 1.E+5 Specific Energy [W-hr/kg] Lidor A., Weihs D., Sher E., Alternative Power-Plants for micro aerial vehicles (MAV), 53 rd Israel Annual Conference on Aerospace Sciences 2

Ragone Chart Curtsey of Lidor A., Weihs D., Sher E. 1.E+9 1.E+8 Ragone Chart 1.E+7 Carbon Nano Tubes Specific Power [W/kg] 1.E+6 1.E+5 1.E+4 1.E+3 1.E+2 1.E+1 1.E+ Metal Spring Pneumatics Shape Memory Alloy Flywheel Phase Change Materials Li-Ion Battery Fuel Cell Internal Combustion Engine Solar Panels Radioisotope Thermoelectric Generator 1.E-1 Synthetic Muscle 1.E-2 1.E-2 1.E-1 1.E+ 1.E+1 1.E+2 1.E+3 1.E+4 1.E+5 Specific Energy [W-hr/kg] Lidor A., Weihs D., Sher E., Alternative Power-Plants for micro aerial vehicles (MAV), 53 rd Israel Annual Conference on Aerospace Sciences 3

Firsts Steps 1 st Solar Vehicle Sunrise II, Nov. 1975 1 st Manned Solar Vehicle Solar Riser, April 1979 1 st Manned Solar Vehicle Gossamer Pinguin, May 198 Crossing the English Channel Endurance Record, 2 Weeks Flight Solar Challenger, July 1981 Qinetiq Zephyr, July 21 André Noth, History of Solar Flight, Autonomous System Lab, Swiss Federal Institute of Technology, Zürich, July 28 4

NASA HALEs (High Altitude, Long Endurance) Pathfinder Pathfinder-Plus Centurion Helios 1994-1998 1998-22 1997-1999 1999-23 7,5 ft, 1998 8,2 ft, 1998 8, ft (goal) 96,8 ft, 21 b = 3m b = 37m b=63m b=75m AR=12 AR=15 AR=26 AR=31 m=25 kg m=315 kg m=86kg m=93kg Dryden Flight Research Center Website, www.nasa.gov [cited: February 213) 5

Main Design Challenge Energy Balance Solar Panels Efficiency Energy Storage Weight / Volume Aerodynamics Structure (Weight) 6

Main Design Challenge Energy Balance Solar Panels Efficiency Energy Storage Weight / Volume Aerodynamics Structure (Weight) Solution MDO: Multidisciplinary Design Optimization 7

Performance, Like Sausages Power Mission Drag Weight Performance Laws, like sausages, cease to inspire respect in proportion as we know how they are made (John Godfrey Saxe, 1869) 8

Analysis Model Date, Time, Location, Attitude Air-Vehicle Geometry Mission Definition Solar Radiation Model Aerodynamic Model Weight Estimation Flight Condition Available Power Drag Polar Vehicle Weight Power Mission Drag Weight Energy Balance Mission Feasibility Performance 9

Solar Radiation Model Based on ESDU formulation Time (date / hour) Latitude / Longitude Altitude Attitude 16 14 12 August 212, Israel Total Solar Irradiance Outside Earth's Atmosphere Total Solar Irradiance at Sea Level Horizontal Surface to the Earth Israel Meteorological Service Watt/Sqrm 1 8 6 4 2 Sunrise Sunset : 2: 4: 6: 8: 1: 12: 14: 16: 18: 2: 22: : Time Engineering Sheet Data Units, "Solar heating: total direct irradiance within the earth s atmosphere," ESDU 6915, September 1975 1

Aerodynamic Drag Estimation FF IF Lift dependent drag Only induced Simple Oswald factor (e =.9) Zero lift drag i, Wing i, Wing Drag bookkeeping Form-Factor Interference-Factor Wing = 1. + 1.44 = 1.1 t c + 2 t c 2 FF IF i, Fuse. i, Fuse. = 1+ = 1 C C D = D i = Fuselage 6 C C D f i ( L W H ) Fuse. Fuse. Fuse. 2 + 1 πar FF IF i i +.25 S W e S C Wet i L Fuse. Fuse. H 2 L Fuse. Roy T. Schemensky, Development of an empirically based computer program to predict the aerodynamics characteristics of aircraft. Volume 1, Empirical methods, Air Force Flight Dynamic Laboratory, AD-78-1, November 1973 11

Weight Estimation Weight Bookkeeping Structure Propulsion system Batteries Solar Panel Payload Motor Weight Estimation A. Noth, "Design of Solar Powered Airplanes for Continuous Flight," Ph.D. Thesis, ETH, Eidgenössische Technische Hochschule Zürich, September 28 12

Structure Weight Estimation mstructure, kg 1 9 8 7 6 5 4 3 2 1 Actual Mass Noth Stender Rizzo Rizzo X 1.5 Icare II Pathfinder Pathfinder Plus m m Structure, Noth Structure, Rizzo 1.5 m m Structure, Rizzo Structure, Stender =.44b 3.1 = 15.19b 1.312 = 22.8b = 8.763b Centurion AR 1.556.25 AR 1.312 AR.5 1 2 3 4 5 6 7 8 AR.311 Helios.5 b, m 13

Mission Definition Sunset Sunset 7, ft <7, ft S.L 2 ft/min 2 ft/min Sunrise Sunrise 14

Mathematical Programming Formulation minf x R s. t. g n ( x) ( x) f(x) cost function Vehicle mass Night time altitude Payload mass x design variables Wing dimension Battery mass g(x) design constraints Energy balance 15

Numerical Implementation Matlab & ESTECO modefrontier environment 16

Design Case A Design Variables Design Variable Battery mass, m Battery Minimum Cruise Altitude Aspect Ratio, AR Wing Span, b Cost Function 1 m Night Time Altitude - Maximize Total Vehicle Mass - Minimize Design Constraint Energy balance Minimum Value 1 kg 5, ft 5 Maximum Value 1 kg 7, ft 4 1 m 17

Design Case A, Pareto Front m Payload = 2 kg m Battery,kg Total Vehicle Mass, kg b,kg (Diameter) Night Time Altitude, ft 18

Design Case A, Pareto Front m Payload = 2 kg m Battery,kg Battery Mass, mbattery, kg 1 9 8 7 6 5 4 3 2 1 55 575 6 625 65 675 7 Night Time Altitude, ft Total Vehicle Mass, kg b,kg (Diameter) Night Time Altitude, ft 19

Design Case A, Pareto Front Designs Wing Span, b, m 15 95 85 75 65 55 45 35 25 15 5 525 55 575 6 625 65 675 7 Night Time Altitude, ft Wing Aspect Ratio, AR 35 3 25 2 15 1 5 5 525 55 575 6 625 65 675 7 Night Time Altitude, ft Wing Area, S, m 2 35 3 25 2 15 1 5 5 525 55 575 6 625 65 675 7 Structural Mass, mstructure, kg 1 9 8 7 6 5 4 3 2 1 5 525 55 575 6 625 65 675 7 Night Time Altitude, ft Night Time Altitude, ft 2

Technology Improvements Design Case A Two main technologies: Solar panels efficiency Nominal 22%, Improved: 4% Batteries energy density Nominal 35 W-hr/kgf, Improved: 5 W-hr/kgf 21

Technology Improvements Total Mass Total mass, kg 2 18 16 14 12 1 8 6 4 2 5 525 55 575 6 625 65 675 7 Night Time Altitude, ft η Sol. =.22 ρ Bat. =35 W-hr/kg η Sol. =.4 ρ Bat. =35 W-hr/kg η Sol. =.22 ρ Bat. =5 W-hr/kg η Sol. =.4 ρ Bat. =5 W-hr/kg 22

Technology Improvements Battery Mass Battery mass, kg 1 9 8 7 6 5 4 3 2 1 5 525 55 575 6 625 65 675 7 Night Time Altitude, ft η Sol. =.22 ρ Bat. =35 W-hr/kg η Sol. =.4 ρ Bat. =35 W-hr/kg η Sol. =.22 ρ Bat. =5 W-hr/kg η Sol. =.4 ρ Bat. =5 W-hr/kg 23

Design Case B Design Variables Design Variable Battery mass, m Battery Aspect Ratio, AR Wing Span, b Cost Function Minimum Value 1 kg 5 1 m Payload Mass - Maximize Maximum Value 5 kg 25 1 m Total Vehicle Mass Minimize Two cases Night time altitude 65 kft Night time altitude 5 kft Design Constraint Energy balance Required Payload Power, Watt 35 3 25 2 15 1 5 2 4 6 8 1 12 Payload Mass, kg 24

Design Case B, Pareto Front 18 16 14 Total Mass, kg 12 1 8 6 Battery Mass, mbattery, kg 6 5 4 3 2 4 2 1 2 3 4 5 6 7 8 9 1 11 Payload Mass, kg Night Altitude 5, ft Night Altitude 65, ft 1 1 2 3 4 5 6 7 8 9 1 11 Payload Mass, kg Night Altitude = 5, ft Night Altitude = 65, ft 25

Design Case B, Pareto Front Designs Payload Mass / Total Mass.16.14.12.1.8.6.4.2 Night Altitude = 5, ft Night Altitude = 65, ft 1 2 3 4 5 6 7 8 9 1 11 Payload Mass, kg (Payload Mass + Battery Mass) / Total Mass.6.5.4.3.2.1 1 2 3 4 5 6 7 8 9 1 11 Payload Mass, kg Night Altitude = 5, ft Night Altitude = 65, ft.7 Structural Mass / Total Mass.6.5.4.3.2.1 Night Altitude = 5, ft Night Altitude = 65, ft 1 2 3 4 5 6 7 8 9 1 11 Payload Mass, kg 26

Conclusions Solar UAV design is a MDO problem Staying aloft forever requires very big vehicles Even for a very modest payload Low feasibility for constant altitude HALE Lower night time altitude is required Crucial importance of improved technologies Main effort: Energy storage weight and volume Solar panels efficiency Structure (Weight) 27