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Solar Powered UAV to set
the World's Endurance Record
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A team of students from the Technion Israel Institute
of Technology, Haifa is working on a new solar powered unmanned aerial
vehicle (UAV) which they hope will soon break a 17 year old world aviation
record. Although solar aviation is nothing new, it is still considered to be
in its infancy. The work done at the Technion as well as elsewhere around the
world is starting to attract the attention of the aviation industry with the
hope of creating green aircrafts with a much higher endurance threshold. Solar
powered UAV history
Sunrise I - the first
ever solar powered drone took to the sky at Camp Irwin Bicycle Lake,
California on November 4, 1974 It was built by the U.S. Company Astro Flight after receiving a
contract through Lockheed to build a flight demonstration model of a solar
powered drone. The Sunrise I used over 1000 solar cells located on the wings
to produce about 450 watts of power. Sunrise I had a 32 foot wing span and
weighed 26 pounds and had a service ceiling of about 20,000 feet on a clear
day. A year later an improved version named Sunrise II took its first flight.
The Sunrise II with it's 4480 solar cells delivered over 600 watts and
weighed only 4 lbs (1.8kg). With more power and a lighter weight the climb
rate of the Sunrise II reached about 300 ft per minute or 20,000 ft per hour
and the service ceiling was estimated to be about 75,000 feet (various
command and control issues limited this number considerably).
The next step in solar
aviation came in 1980. The U.S. Company AeroVironment (who invented the
ultra-light airplane), backed by the Dupont Corporation, attempted to build a
solar-powered piloted aircraft that could fly from Paris, France to England.
The first prototype, called the "Gossamer Penguin", was fragile and
not very airworthy, but led the way to an improved version called the
"Solar Challenger". The Solar Challenger had a wingspan of 14.3
meters (47 feet) and a weight of 200lbs (90kg). It had 16,128 photovoltaic
cells that covered the wings, with a total output power of a whooping 2,600
watts. The Solar Challenger was capable of reaching an altitude of 12,000
feet, and in July 1981 the aircraft became the first to cross the 163 miles
(262km) distance from Paris to Manston in the UK only using solar
power.
The success of the
Solar Challenger sparked an increasing interest among the US Government
regarding solar flight the and the funding of research into high altitude
long endurance solar powered drones. Due to this, AeroVironment was able to
begin work on the High Altitude Solar (HALSOL) drone project, which was first
launched in June 1983. HALSOL is a simple flying wing, spanning 98 feet (30
meters). The main wing was made of carbon fiber Styrofoam and Kevlar covered
by thin Mylar plastic film making it light and extraordinarily strong. The
development of the HALSOL was conducted in secrecy and nine HALSOL flights
took place in the summer of 1983 at the Groom Lake base in Nevada (where the
legendary F-117 stealth bomber, which entered service the very same year, was
tested). The flights were conducted using radio control and battery power,
since the aircraft had not yet been fitted with solar cells. HALSOL's
aerodynamics was validated, but the tests led to the conclusion that
photovoltaic technology had not matured enough at that time. It took more than 10
years before the HALSOL project was revived, this time by NASA. The now modified
solar aircraft named Pathfinder reached an altitude of 50,500 feet on
September 11, 1995, setting a new altitude record for solar-powered aircraft.
Three years later modifications to the Pathfinder resulted in a longer-winged
version called Pathfinder-Plus. On August 6, 1998, the modified aircraft was
flown to a record altitude for propeller-driven aircraft of 80,201 feet. The
goal of the flight was to validate new solar, aerodynamic, propulsion and
systems technology developed for the Pathfinder's successor, the Centurion,
which was designed to reach and sustain altitudes within the 100,000-foot
range. The Pathfinder-Plus incorporated several improvements to the original
Pathfinder. One of the more noticeable features being stronger solar cells
with 19% efficiency (the original Pathfinder had only 14%) developed by SunPower Corp. in Sunnyvale,
California. The new silicon solar cells boosted the maximum potential power
from about 7,500 Watts on Pathfinder to about 12,500 Watts on
Pathfinder-Plus.
The Centurion, like its
immediate predecessors Pathfinder and Pathfinder-Plus, was a lightweight,
solar-powered, remotely piloted flying wing that demonstrated the technology
of applying solar power for long-duration, high-altitude flight. The
Centurion had more than twice the wingspan of the Pathfinder and about 2/3
more than the Pathfinder-Plus (98 feet in the Pathfinder and 206 feet
Centurion). The Centurion's test flights were done by NASA in 1998 and a year
later was modified and renamed the Helios (after the Greek sun god).
Helios is the most
ambitious of NASA's solar UAV projects to date. With a 247-foot wingspan
(greater than a 747 Jumbo Jet), 62,120 bi-facial solar cells and a projected
maximum flying altitude of 100,000 feet, the Helios is the peak of two and a
half decades of solar aviation research. Like its predecessors the Helios was
built by AeroVironment and has been used on the Environmental Research
Aircraft and Sensor Technology (ERAST) program. The Helios applies hybrid
technology – solar energy using photovoltaic cells by day and fuel cells by
night. The Helios was designed to be the forerunner of high-altitude unmanned
aerial vehicles that could fly ultra-long duration environmental science or
telecommunications relay missions lasting for weeks or months without using
consumable fuels or emitting airborne pollutants. On August 13, 2001, Helios
demonstrated its capability when it reached an unofficial altitude record for
non-rocket-powered aircraft of 96,863 feet. Unfortunately, on June 26, 2003
during a test flight over the Pacific Ocean near Kauai, Hawaii the Helios
prototype was lost due to a structural failure caused by control
problems. Existing and
future solar powered UAV projects
In recent years
European countries are taking a more central role in the development of High
Altitude / Long Endurance (HALE) solar powered UAVs. Several projects are
either on going or being planed for advanced solar powered vehicles. From
2000-2003 a team from the Politecnico de Torino in Italy together with a team
from the University of York in the U.K developed a concept for the Heliplat -
a Very-Long Endurance Solar Powered Autonomous Aircraft (VESPAA). Heliplat
and other VESPAA UAVs could play the role of a "pseudo satellite",
with the advantages of being closer to the ground, more flexible and at a
cost much less than a real satellite.
Heliplat-like HALE
flying above a major city will be able to cover an area 1000 km across, and
process a predicted 425,000 cell phone conversations simultaneously. This
means a user community of 8.5 million per unit (although this does not take
into account data transmission).
While the Heliplat was
designed to have a large wingspan (70 meters), the German Aerospace Center
(DLR) is currently designing a much smaller HALE known as the SOLITAIR.
The SOLITAIR will only have a 5.2 meter wingspan and four solar panel
sections embedded into its body that will use small engines to rotate towards
the sun. Like the Heliplat, the SOLITAIR is also being developed in order to
replace some of the tasks currently done by satellites. Other interesting
projects currently under development in Europe are the Zephyr
light weight HALE UAV developed and tested by the U.K. company QinetiQ, and
the ultra-light weight (2.5 kg) Sky-Sailor
developed by the ETH university in Zurich, Switzerland for a
possible future mission to mars. Sunsailor UAV
project at the Technion
In 1990 Dr. Wolfgang
Schaeper from Germany set the world distance record in a closed circuit for a
small (Category F5) solar Radio Controlled Flight UAVs. Schaeper's 190km
record approved by the Fédération Aéronautique Internationale (FAI) stood
unchallenged for more than 17 years, but now a team of nine students from the
Technion is developing what they believe might be the next contender. In July
2006 the team tested the SunSailor, a 90 watt ultra light weight solar UAV
capable of 11 hours of sustained flight using 84 20% efficiency A300 solar
panels. During the first attempt to break the record the team reached only
25km before the SunSailor crashed to the ground due to flight control
problems. The team immediately began work on a second prototype,
appropriately named SonOfSunSailor, which took to the skies only two months
later. After a 40 minute successful flight test the team was optimistic that
the SonOfSunSailor (an improved version with an output of 140 watt) would be
able to break the record. On September 4,2006 another attempt was made which
ended in another crash. Although, solar
aviation is nothing new, it is still in its infancy. To date only prototypes
and demonstrators have been using solar energy as their main source of power.
No commercial or known operational military UAV is currently using solar
energy. But the Technion's small experimental drone has sparked some interest
in the industry. The Israeli Aircraft Industries (IAI), one of the largest
manufacturers of UAVs in the world, decided to give support to the SunSailor
and its team. A third attempt is planned for around May 2007 and with the
previous problems fixed the team believes it can break the world
record.
TFOT
recently covered several other ground braking projects developed by students
from the faculty of aerospace engineering in the Technion. Students, under
the supervision of Prof. Benjamin Landkof and Robert Zickel, worked on
developing a concept for UAV
to UAV refueling. A different team worked on developing a small
canister launched UAV equipped with day/night cameras and weaponry (both
lethal and non lethal). Both projects as well as the SunSailor were put on
display at the 47th
Israel Annual Conference on Aerospace Sciences, that took place on
February 21, 2007 in Tel Aviv and at the Technion. In 2006 TFOT covered
another Technion project to develop a high speed ramjet
rocket called Ramtech which was successfully tested on May 9 of
that same year, near the coast of Palmachim. Sunsailor interview
To learn more about the
Sunsailor, TFOT
talked to Professor Omri Rand, head of the faculty of Aerospace Engineering
at the Technion as well as interviewed Idan Regev from the IAI (who was one
of the nine students who worked on the project). Q: When did the SunSailor project begin and how many people
participated in it? A: The
project began on spring 2005. 9 final year undergraduate students took the
challenge and started designing the soon-to-be-launched SunSailor with the
guidance of faculty staff and the supervision of Mr. Shlomo Tsach of the IAI.
The real beginning of the project started a few months before that when one
of these students, Hanan Levy, came to me with the idea of breaking a "green"
world record. The idea was soon nurtured by Prof. Benjamin Landkof who made
this project possible. So, that's how it all started. During the flight tests
we had many undergraduates and graduates students that helped us out. Q: What was the purpose and motivation of the project?
A: There were
three main purposes here. One is obvious and driven by the faculty education
to always going further, higher and longer, even if that means breaking the
world record. The second was a more selfish one, as final year students both
we and the staff saw this as a great opportunity to apply all that we have
learned – the theory, to reality and gaining the priceless experience
of DBF – Design, Build and Fly. The third and probably the most ambitious
purpose has been to set off an avalanche of solar technology use throughout
the whole Israeli Hi-tech industry. Here you must bare in mind two important
facts. The first being that the space and aviation industry products of today
are tomorrow's every household products, i.e Magnesium lightweight
structures, athletic shoe design and water purifiers are all Apollo program
products. Second fact is that Israeli Hi-Tech companies set the standard for
the future of millions of people in and outside of Israel. These two combined
with the most appealing idea of a solar powered UAV can change the future for
the better and this is the third, hidden purpose. Q: Could you briefly describe the Sunsailor project? A: The
project started out with a preliminary design dictated mostly by the FAI
regulations for achieving the record. After insuring feasibility the students
completed the design and started manufacturing the SunSailor at the Aerospace
Engineering Faculty's workshop. This SunSailor completed 6 flights before
crashing. The next one, that was built after a short redesigning process was
built at the Technion in between the sirens of the Second Lebanon War that
were sounded in Haifa in July/August 2006. This improved version was made,
with the generous help of the IAI, in a record time of 54 days. After it
crashed it took only a few days until we started building the third SunSailor
at the IAI with the constant help and support of the Technion. Q: What's next for the Sunsailor? A: The
SunSailor intends on breaking the World record and probably a few more
surprises to come. Q: What do you see as the biggest obstacle in creating a functioning
commercial solar UAV? A: The
greatest obstacle is probably reliability. Especially in the civil market,
reliability is very important. We have noticed that these systems, being very
light-weight and having many problems, starting from structure to control
issues are our main concerns. The solar panels are not that reliable as they
must be handled carefully and there's not much redundancy available. The last
thing is the initial price. These products are going to cost almost twice as
much than other UAVs of their size. However, after only a short period of
usage, it will pay for itself as there's no fuel and pollution costs and time
between landings is not a day or two but more likely to be a few weeks. Q: Commercial Photovoltaic cells still have fairly low efficiency
(typically >20%). At what level of efficiency do you believe they will
start proving to be more useful in commercial aviation (both manned and
unmanned)?
A: Truthfully,
Solar cells low efficiency is only half of the problem. The means of energy
storage such as rechargeable batteries or fuel cells is the other half. But
solar cells for large scale commercial aviation will have to go a long way
before they can supply the power that is needed. Even a 40% solar cell
covered wing on a sunny day will barely be enough for the cruise power
requirements of a small manned aircraft. Q: NASA's Helios was designed as a hybrid UAV using both solar panels
and fuel cells. Do you believe this is the way to go for future solar UAVs? A: Solar
power alone is not enough. During night time and even during the day (for
large scales) the UAV must have an energy storage capability. Even if you fly
above the clouds at a low altitude around the equator you can not catch the
sun, the earth turns faster than an electric powered aircraft can, so a 24
hours flight will have to be hybrid. Q: Could you try and estimate what are we going to see in 5-10 years in
term of solar powered UAVs in the world (when will we see the first solar
powered commercial / military UAV and what will it be used for?) A: In 5 years
from now we will be able to see solar powered private/military small scale
UAVs monitoring large areas of farms or woods and conducting various border
control missions. In 10 years we will be able to see the first successful
commercial Long Endurance High Altitude UAVs that will enable
"semi-satellite" use for communications and observation. Finally,
if Solar cells and Energy storage devices keep advancing at the current rate,
I believe that 50 years from now, Hybrid HALE UAVs will substitute most of
today's satellites. Q: How does the IAI see its role in the development of future solar
powered UAVs (what "niche" will they occupy?) A: Currently
the IAI is testing the technology and aims to apply it in the future wherever
it is feasible and needed. |
