Home' Asian Aviation : AAV April 2010 Contents AsianAviation | APRIL 2010 21
When the Wright brothers
completed the first
ights of a heavier-than-
air aircra in December
1903, none of the first
three tests covered a distance of more than 200 . Still,
the ights marked a triumph of human invention over
multiple engineering challenges, even though many
problems still remained before aviation could really
come into its own.
Just 16 years later, Alcock and Brown completed
the rst non-stop transatlantic ight. While that
pioneering e ort came to an ungraceful end -- the
modi ed Vickers Vimy aircra crash-landed in an
Irish bog -- it was still a success and a clear indication
of the potential of air travel.
ese days, aviation is so much a part of everyday
life that such dramatic technological breakthroughs
are rare. Yet April has seen a major step towards just
such a milestone, with the maiden ight in Switzerland
of a prototype of the most ambitious solar-powered
aircra programme to date : Solar Impulse.
e ultimate goal of the programme is extraordinary:
to build an aircra that will circumnavigate the globe,
non-stop, carrying two pilots and no fuel whatsoever.
Instead, the vehicle will rely exclusively on solar energ y
to power its electric motors and charge batteries that
will keep it ying at night.
e aircra that took to the air for its rst fully-
edged test ight (a 350m short hop ight, just
1m above ground, had already been completed in
December 2009) is a single-seat prototype, dubbed
HB-SIA. This model is designed to stay aloft
continuously for up to 36 hours and will be followed
by a larger single-seater, HB-SIB, which will be limited
in its ight duration only by the pilot's endurance.
Eventually, improved battery e ciency will yield
further weight reductions that will permit the
construction of a two -seat aircra . is one, it is
hoped, will be able to complete a
non-stop ight around the world.
For now however, the Solar
Impulse team, led by Chairman and
project initiator Bertrand Piccard, can take satisfaction
in the success of HB-SIA.
Before thousands of spectators, the aircra took
o from Payerne air eld, in the west of Switzerland,
at 10:27am on 7 April and completed a ight lasting
one hour 27 minutes, attaining an altitude of 1,200m
(3,937 ). Test pilot Markus Scherdel spent the time
familiarizing himself with the aircraft's handling
before returning to land.
" is rst ight was for me a very intense moment,"
Scherdel said on stepping out of the aircra . " e
HB-SIA behaved just as the ight simulator told
us. Despite its immense size and feather weight, the
aircra 's controllability matches our expectations."
In fact, the aircra has a wingspan of 63.4m -- about
the same as an Airbus A340 -- while being just 21.85m
in length. Meanwhile, huge e orts have been put into
keeping the loaded weight down to 1,600kg -- about
the same as an average family car.
e aircra is built around a carbon- bre composite
honeycomb sandwich structure. The upper wing
surface is covered with a skin of encapsulated solar cells
and the underside comprises a high-resistance, exible
lm. Inside the wing , 120 carbon- bre ribs, placed
50cm apart, maintain its aerodynamic cross-section.
e Solar Impulse energ y capture system comprises
11,628 monocrystalline silicone solar cells, each just
150 microns thick and selected for their lightness and
exibility. eir energy e ciency could be higher --
it is now 22 percent -- but they remain the optimum
solution for now.
e project's biggest weight challenge is carrying the
batteries needed to keep the aircra ying at night. In
HB-SIA, the solution is the carriage of about 400kg
of lithium polymer batteries -- accounting for about a
quarter of the aircra 's total weight.
Beneath the aircraft's slender wing are four
gondolas, each containing a 10hp electric motor,
a lithium polymer battery set and a management
system controlling electrical charge/discharge and
temperature. ermal insulation protects the systems
from temperatures of -40 degrees Celsius encountered
at 8,500m altitude. Each engine also has a reducer that
limits the rotation of the aircra 's 3.5m, twin-bladed
propellers to 200-4,000rpm.
HB-SIA is the fruit of seven years' work that began
with a feasibility study at the Ecole Polytechnique
Federale de Lausanne (EPFL). e project is funded
in part by private partners including Solvay, Omega,
Deutsche Bank and Bayer Material Science. The
official scientific partner is the EPFL, alongside
engineering partner Altran and advisory aircraft
manufacturer Dassault Aviation.
e second aircra , HB-SIB, with a pressurized
cockpit and advanced avionics, is scheduled
for completion in 2011. If all goes according to
plan, HB-SIB will embark in 2012 on a ve-stop
circumnavigation of the globe, expected to last 20-25
"We still have a long way to go until the night ights
and an even longer way before ying round the world,
but today ... an essential step towards achieving our
vision has been taken," Piccard said a er the ight.
"Our future depends on our ability to convert
rapidly to the use of renewable energies," he continued.
"Solar Impulse is intended to demonstrate what can
be done already today by using these energies and
applying new technologies that can save natural
ere is indeed a long way to go. But the earliest
aviation pioneers proved a century ago that huge
technological leaps can quickly follow the rst short
Andrzej Jeziorski / Vancouver
The HB-SIA test aircraft is designed to stay aloft under solar power
for up to 36 hours. CREDIT: SOLAR IMPULSE
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