Solar Impulse’s first prototype solar-powered aircraft completed a European promotional tour this year, in the run-up to a planned non-stop, round-the-world flight in 2014, writes Andrzej Jeziorski.
On Sunday, 3 July, Solar Impulse aircraft HB-SIA landed back at Payerne in Switzerland, bringing to a close the revolutionary solar-powered aircraft’s European tour as the team gears up attempt a non-stop circumnavigation of the globe in 2014.
The prototype, piloted by Solar Impulse co-founder and Chief Executive Officer Andre Borschberg, touched down in the evening in Payerne after a 12-and-a-half hour flight, powered by solar energy alone. Solar Impulse says its European promotional flight campaign was “highly successful”, with Borschberg and Solar Impulse founder and President Bertrand Piccard meeting – among many others – several high-level political and financial figures.
“The feedback from our European flight campaign is encouraging,” says Piccard. “The welcome we received from political and industrial circles in Brussels and Paris shows that Solar Impulse is pioneering a new way of thinking in terms of renewable energy and energy saving.”
[Subhead:] Brussels visit
In Brussels – as guests of the President of the European Parliament, the President of the European Council and of the European Commission – the Solar Impulse team actively promoted new technologies and renewable energies with the aim of reducing dependency on fossil fuel. From there, the team travelled to Paris as special guests of the International Air and Space Show at Le Bourget.
The aircraft, with Borschberg at the controls completed three international flights during the European campaign: a 630 km leg from Payerne to Brussels on 13 May; 395km from Brussels to Paris-Le Bourget on 14; and 426km from Paris-Le Bourget to Payerne on 3 July.
The flights were part of a long run-up to the team’s ultimate goal: a round-the-world flight scheduled for 2014. “These flights have provided good learning opportunities in terms of slotting the solar aircraft into international air space and landing at international airports,” Solar Impulse says.
“This solar plane is an extraordinary example of what we can do with stored energy,” Borschberg says. “The welcome we received in Brussels and Paris was highly motivating for the team as we enter phase two of the project which is building a second plane to fly around the world.”
The ultimate goal of the programme is ambitious: to circumnavigate the Earth, non-stop, carrying two pilots and no fuel whatsoever. Instead, solar energy will power the aircraft’s electric motors and charge batteries that will keep it flying at night.
HB-SIA is a single-seat prototype – a precursor to the two-seat aircraft that will attempt the round-the-world mission. The aircraft took to the air for its first time on 7 April 2010, completing an 87-minute flight up to an altitude of 1,200m (3,937ft). Since then, the aircraft has been constantly pushing back boundaries and breaking records.
The first prototype 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 flight duration only by the pilot’s endurance. Eventually, improved battery efficiency will yield further weight reductions that will permit the construction of a two-seat aircraft. This last is the one that will be used for the non-stop round-the-world flight.
HB-SIA has a wingspan of 63.4m – about the same as an Airbus A340 – while being just 21.85m in length. Huge efforts have been put into keeping the loaded weight down to 1,600kg – about the same as an average family car.
The aircraft is built around a carbon-fibre composite honeycomb sandwich structure. The upper wing surface is covered with a skin of encapsulated solar cells and the underside comprises a high-resistance, flexible film. Inside the wing, 120 carbon-fibre ribs, placed 50cm apart, maintain the aerodynamic cross-section.
The Solar Impulse energy-capture system comprises 11,628 monocrystalline silicone solar cells, each just 150 microns thick and selected for their lightness and flexibility. Their energy efficiency could be higher – it is now 22 percent – but they remain the optimum solution for now.
The project’s biggest weight challenge is carrying the batteries needed to keep the aircraft flying at night. In HB-SIA, the solution is the carriage of about 400kg of lithium polymer batteries – accounting for about a quarter of the aircraft’s total weight.
[Subhead:] Electric motors
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. Thermal 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 aircraft’s 3.5m, twin-bladed propellers to 200-4,000rpm.
“Our future depends on our ability to convert rapidly to the use of renewable energies,” Piccard said on the occasion of the first aircraft’s maiden flight. “Solar Impulse is intended to demonstrate what can be done already today by using these energies and applying new technologies that can save natural resources.”