Around-the-world solar airplane passes first flight test

June 4, 2014

Solar Impulse 2 made a two-hour maiden flight over Switzerland June 2. Photo courtesy of Solar Impulse.

The goal of an around-the-world flight powered only by solar energy seemed a bit closer to reality after the aircraft designed to accomplish the mission completed a first flight test in Switzerland on June 2.

Test pilot Marcus Scherdel piloted the aircraft for two hours and 17 minutes on its first flight, Vincent Colegrave, spokesman for the Solar Impulse initiative, said in an email. High-speed taxi testing had been carried out the previous day.

More pre-certification test flights will be required in the coming months, Colegrave said. An attempt to achieve the "ultimate goal" in the aircraft, dubbed Solar Impulse 2—successor to the prototype aircraft Solar Impulse 1—is planned for next year.

A series of videos documenting the maiden flight of Solar Impulse 2 from Payerne Aerodrome were posted on the project’s website, where a sense of exuberance was evident and "a huge emotional step for the entire team" was proclaimed in a blog about the flight. That was a markedly different mindset among team members than in mid-2012, when Solar Impulse 2 experienced the crushing disappointment of a wing spar breaking during a torsion test, a setback that dashed hopes for an alternative-energy-powered dash around the globe in 2014 for the project co-founded by Bertrand Piccard and Andre Borschberg.

In contrast with the prototype, "Si2" incorporates "a vast amount of new technology" geared toward enhanced efficiency and long-haul flying, the team said.

"It is the first aircraft that will have almost unlimited endurance," it added.

To realize that capability, solar energy will be collected in 17,248 solar cells, and stored in lithium polymer batteries mounted in the four 17.5-horsepower engines’ nacelles. The aircraft will save energy by climbing during the day to an altitude of 8,500 meters (about 27,900 feet) and descending by night to 1,500 meters, or about 5,000 feet. Solar cells are mounted on the wings, fuselage, and horizontal tail—and the wingspan, at 72 meters, is wider than a Boeing 747’s, Solar Impulse said.