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Case Studies:
Design of Solar Powered Airplanes
23.11.2015 14 Fixed Wing UAS: Control and Fuel Case Studies
Philipp Oettershagen, Autonomous Systems Lab
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Motivations Today, 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 UAVs
Introduction: Why Solar Powered Flight?
24.11.2015 15 Fixed Wing UAS: Control and Fuel Case Studies
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Working Principle of Solar-Electric Airplanes
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Possible Solar UAS Applications
www.telegraph.co.uk
Yingxiu, May 15th 2008
Wildfires in California October 2007 Altair/SR
Disaster Scenario / Search and Rescue Agricultural and industrial inspection
High-Altitude Long Endurance (HALE) Early Wildfire Detection
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Premises of solar aviation with model
airplanes
first flight of a solar-powered airplane:
4th 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
Sunrise II, 1975 Wingspan 9.76 m
Mass 12.25 kg
4480 solar cells 600 W; Max duration: 3 hours
Solaris, 1976
Solar Excel, 1990 MikroSol, PiciSol, NanoSol 1995-1998
23.11.2015 18 Fixed Wing UAS: Control and Fuel Case Studies
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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)
1st solar manned flight without energy storage: Gossamer Penguin of Dr. MacCready (US) in 1979.
Next version: Solar Challenger crossed the
English channel in 1981
Introduction – History of Solar Flight
Solar Riser, 1979
Gossamer Penguin, 1980
Solar Challenger, 1981
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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 solar-powered manned airplanes)
Introduction – History of Solar Flight
Solair I, 1981
Sunseeker, 1990
Icare 2, 1996
Solarimpulse, 2010
23.11.2015 20 Fixed Wing UAS: Control and Fuel Case Studies
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The way to High Altitude Long Endurance (HALE) platforms
1st 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
Qinetiq (UK) built Zephyr in 2005 December 2005 : 6 hours at 7’925 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)
Introduction – History
of Solar Flight
Zephyr, 2005
Solong, 2005
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23.11.2015 Fixed Wing UAS: Basics of Aerodynamics 23
Google - Titan Facebook - Aquila
50 m
160 kg
19 km
42 m
400 kg
18-28 km
Airbus - Zephyr
22.86 m
50 kg
19.8 km
High Altitude Long Endurance platforms today
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How do I do this?
What performance can I expect?
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
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Solar-powered UAV Conceptual Design: A Tool
Run (constrained)
optimization
Core Module: Aerodynamics Power Train Mass Estimation Structure Dimensioning
Environment Altitude, latitude, longitude, day, ...
Design variables: Wingspan, aspect ratio, battery mass
Technological parameters: Efficiencies, mass models, rib or shell wing
Payload Mass, power consumption
Performance Evaluation Simulation of the Day Mode of Operation:
Allow variable altitude yes/no
Masses Polars
Endurance / Excess Time / Charge margin
Max. Altitude for Continuous Flight
23.11.2015 25 Fixed Wing UAS: Control and Fuel Case Studies
[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. 545-561
Design variables
Technological parameters (inputs) User parameters (inputs)
Performance metrics (outputs)
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Performance Metrics (1/2)
Time12 h 24 h
Power
E_batSolar Power
Required
Power
Endurance
Excess
time
Time12 h 24 h
Power
E_bat
Solar Power
Required Power
23.11.2015 26 Fixed Wing UAS: Control and Fuel Case Studies
Case 1: • Perpetual flight not possible
• Performance metric:
• Tend (Endurance). Tend can be
>24h (even though continuous
flight is not possible)
Case 2: • Perpetual flight possible
• Performance metrics:
• Excess time Texc
• Minimum state of charge
• Charge margin Tcm
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Performance Metrics (2/2)
If perpetual flight is possible, we define:
In the conceptual design phase, we optimize both Texc and Tcm to
generate sufficient safety margins for perpetual flight!
Ebat Battery energy [J]
SoC Battery state of charge [%]
Poutnom Nominal required output power [W]
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Basic System Modeling (1/2)
Forward-integration of state equations:
Power modeling
I Solar irradiance [W/m²]
Asm Solar module area [m²]
ηsm, ηmppt Solar module and maximum power point
tracker efficiency [-]
Pav, Ppld Avionics and payload power [W]
ηprop Propulsion system efficiency
mtot Total airplane mass
I = I (day,t,lat,h)
| | Autonomous Systems Lab 23.11.2015 Fixed Wing UAS: Basics of Aerodynamics 29
Basic System Modeling (2/2)
To derive the level flight power (constant altitude flight), we combine
v Airspeed [m/s]
Awing Wing area [m²]
CD, CL Drag / Lift coefficients [-]
ρ Local air density [kg/m³]
with
and minimize the resulting expression w.r.t. the airspeed to yield
CD and CL 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, mtot=6.9kg,
Awing=1.7m², vopt=7.6m/s, Plevel=21W.
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Scaling of mass seems easy at first glance [6,7]:
Fixed Wing Aircraft
Mass Models (1/2)
3W L mg b
2S b
/W S b1
31/W S k W
[6]
(Assumption: Geometric similarity)
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Mass Models (2/2)
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Structure mass is
depending on:
Payload (mass)
Payload location/distribution
Wing geometry (also airfoil!)
Structure concept
Load cases
Improvements to the
Mass Models
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Payload 100 passengers, 12000 kg
Speed: 600 km/h
Height: 12 km: = 0.31 kg/m3
Wing area and mass for AR=10:
Power for level flight / Drag:
Assume glide ratio 1:30 CD=CL/30
Solar Power Irradiance: max. 1.4 kW/m2
Example: Solar
Powered Airliner?
L
LCV
mg
AR
bAC
2
2 25.0
kgm
043.0 25.0
1.3
ARb
m
mmmm
pld
structpropulsionpld
m ≈ 13 t (unrealistically light),
b ≈ 24 m, A ≈ 57 m2
kW 6802
3 VACP Dlevel
It is – unfortunately – far
from being realistic…
23.11.2015 34 Fixed Wing UAS: Control and Fuel Case Studies
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Low-altitude
perpetual flight
(700m AMSL)
Current
technology
Aspect ratio 12
Minimal payload:
0.6kg, 7W
Latitude
37.34°N
June 21
Skyclear
Conceptual Design Results (1/1)
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39
Hand-launchable and rapidly deployable
Fully autonomous, minimal supervisory requirements
Versatile sensor payload
AtlantikSolar UAV
Wingspan 5.65 m
Mass 6.9 kg
Nominal cruise speed 10 m/s
Minimum endurancea 13 hrs
Record endurance 81.5 hrs
Max. solar power 280 W
Power consumption 43 W a – full battery with no solar charging
For student projects, please contact us! (e.g. [email protected])
Solar-powered UAV Design Example
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Conditions
Excellent irradiance
Significant thermals
during the day
Achievements
Duration: 81h23m
Distance: 2316km
Av. airspeed: 8.6 m/s
P_mean: 43W+15W
SoCmin: 39%
World record in flight
endurance for all
aircrafts with mtot<50kg
Flight-endurance record: 81h flight (14.07.15)
Continuous flight proven to be
feasible with good energetic margins
and without using thermals or
potential energy storage
24.11.2015 40 Fixed Wing UAS: Control and Fuel Case Studies
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Technical Progress and Scaling Considerations
Energy Generation and Storage
24.11.2015 41 Fixed Wing UAS: Control and Fuel Case Studies
Absolute
Characteristics
SkySailor
(2008)
SenseSoar
(2012)
AtlantikSolar
(2014)
mtot 2.5kg 5.1kg 7.0kg
Wing span 3.2m 3.1m 5.6m
Battery mass 1.05kg 1.9kg 2.9kg
Aspect ratio 13 12 18.5
Psolarmax 90W 140W 280W
Ebat 252Wh 460Wh 710Wh
Technological
Progress
SkySailor
(2008)
SenseSoar
(2012)
AtlantikSolar
(2014)
ηSolarModule 17% 19% 23%
ebat 240Wh/kg
(Li-Ion)
245Wh/kg
(Li-Ion)
255Wh/kg
(Li-Ion)
Slow but steady
progress on PV and
battery technology!
But sensors and
avionics have
minituarized, too.
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Communication
Primary: 3DR radio
Long-Range: Iridium SATCOM
Radio control: Spektrum
Autopilot and Sensors
IMU: ADIS16448
Airspeed Sensing: Sensirion SDP600
GPS: U-Blox Lea-6H
uBlox
Sensorpod
First person view goggles
External cameras
Optical cameras: Aptina MT9V034, IDS UI-3251LE
Thermal camera: FLIR Tau 2
APPLICATIONS
Sony HDR AS100V
GoPro Hero 3 silver
Robust EKF-based State estimation
Simultaneous Localization and Mapping (SLAM)
Human detection
Pixhawk PX4 Autopilot
Agricultural inspection Leutenegger, S.; Melzer, A.; Alexis, K.; Siegwart, R.,
"Robust state estimation for small unmanned
airplanes," in Control Applications (CCA), 2014
Avionics Perception
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Visual-inertial SLAM sensor
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.431–437, 2014
Sensorpod: Sensor and Processing Unit
Developed at ETH Zurich
FPGA board for visual-inertial odometry
Hardware synchronized IMU and camera data
Up to four cameras
| | Autonomous Systems Lab 23.11.2015 48 Fixed Wing UAS: Control and Fuel Case Studies
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[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. 17505, 2007
[5] R.W. Beard and T.W. McLain. Small Unmanned Aircraft: Theory and Practice. Princeton University
Press, 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 Expanded
Edition, 2009. MIT Press. Paperback ISBN 978-0-262-51313-5
[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. 545-561, DOI:
10.1007/s10846-010-9484-x
References
23.11.2015 49 Fixed Wing UAS: Control and Fuel Case Studies
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Thanks for your attention! Questions?
23.11.2015 50 Fixed Wing UAS: Control and Fuel Case Studies