What has a wider wingspan than a 747, weighs the same as a car, and
can fly almost forever without a drop of fuel? If you were in Payerne,
Switzerland on Wednesday, you would have seen the answer as psychiatrist
and explorer Bertrand Piccard and engineer and entrepreneur André
Borschberg unveiled the Solar Impulse 2. The result of 12 years work,
the ultra-light, solar-powered airplane will attempt to fly around the
world next year relying exclusively on solar power to keep it aloft for
days and a time.
Attended by luminaries such as Swiss Councilor Ueli Maurer and Prince
Albert of Monaco, and representatives of the various companies that
contributed sponsorship and technology to the project, the début of the
Solar Impulse 2 marks the culmination of 12 years of effort by 80
technicians. It builds on the success of the previous Solar Impulse, which set eight world records, including a flight across the United States that saw the first day/night flight by a solar-powered plane.
The Solar Power 2 is a single-seater aircraft built of carbon
composites with a 72-m (236-ft) wing span, which is larger than that of a
Boeing 747-8 and 8 m (26 ft) wider than the previous Solar Impulse.
Despite this huge expanse, it weighs only 2,300 kg (5,070 lb), of which
633 kg (1,395 lb) are lithium-ion batteries used to power the plane's
four 17.5 hp electric motors that spin the propellers with an efficiency
of 94 percent.
During daylight hours, the power to run the plane comes from the top
of the wing, which is covered with flexible solar panels that conform to
the wing’s curve. A central truss makes up the fuselage, and the wings
are formed from a complex latticework of composites. According to
Piccard, this new construction is much lighter than the first Solar
Impulse with the composite fabric cover weighing a mere 25 g/sq m. The
entire plane was also designed for a high degree of reliability to allow
it to remain aloft for 12 hours without maintenance, yet keeping the
weight trimmed to a minimum.
The solo pilot for the round-the-world attempt will sit in the 3.8
sq-m (40.9 sq-ft) cockpit, which was designed using computer-aided
ergonomic simulations and is described as a "business class seat" for
the circumnavigator, complete with lumbar massage and the ability to
convert into a bunk so the pilot can catch a nap during the five-day
ocean crossings. Everything from using an oxygen supply to eating, and
even sleeping were tested on the ground using a flight simulator while
the pilot’s vital signs were monitored.
To save weight, the cockpit isn't pressurized, nor is it heated.
Instead, the pilot relies on an oxygen supply stowed in the cabin area
for high altitude flight and both the pilot and batteries are protected
against the subzero temperatures by a new insulating foam developed by
Bayer.
However, the cockpit is hardly a return to the days of Alcock and
Brown. There’s an autopilot that the designers refer to as a "virtual
co-pilot" that can alert the pilot in an emergency via a wrist-mounted
alert buzzer, and the flight will be followed by a ground-based mission
control that measures 50,000 parameters to modify the flight plan while
under way. Communications with control is by means of a satellite
communications system by Swisscom, which weighs less than 5 kg (11 lb),
and is connected to what the team says is the lightest satellite antenna
in the world – it's so light that a Swisscom logo serves as the
counterweight.
The Solar Impulse 2 isn't fast, with a top speed of 45 mph (72 km/h),
but Piccard says that its endurance is that if its pilot. It operates
at 28,000 ft (8,500 m) during the day as it stores solar energy, then
descends during the night, using the drop in altitude to maintain
airspeed without drawing on the batteries, until it reaches a second
cruising altitude between 6,000 and 9,000 ft (1,800 and 2,700 m) and
goes back on battery power.
Despite all this, the plane is very heavy to control in turbulence.
Taking off and landing are scheduled for early morning and after dark to
avoid turbulence and heavy air traffic. This restricts takeoff and
landings to very calm conditions, and landing and takeoff need to be
carefully planned in advance because the plane has a minimal
undercarriage. This means that to keep the wings stable on takeoff and
landing, the ground crew use electric bicycles to hold the wings up on
takeoff and catch them again on landing like a very low budget version
of Thunderbirds. They grab on to posts suspended from the plane, which
are also equipped with small wheels, so the Solar Impulse 2 can make
emergency landings.
Piccard, compares this to conditions of the earliest heavier-than-air
aviators and calls the Solar Impulse 2 the start of a new cycle of
aviation.
As to the future, ground tests are under way, which will be followed
by flight tests in Switzerland in May, a public air show debut later
this year, and the round-the-world attempt in March 2015. If all goes
according to schedule, the Solar Impulse 2 will fly over the Arabian
Sea, India, Burma, China, the Pacific Ocean, the United States, the
Atlantic Ocean and Southern Europe or North Africa before returning to
its starting point in the United Arab Emirates. Along the way, the plane
will land periodically to change pilots and participate in public
events.
'A vision counts for nothing unless it is backed up by action. With
eight world records for Solar Impulse 1, the first solar aircraft
capable of flying during the night, crossing two continents and flying
over the United States, we have shown that clean technologies and
renewable energies can accomplish the impossible,” says Piccard.
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