If there is a windless, rain-free day over Payerne between the bad weather fronts, then the chances are good that there will be another Solar Impulse test flight. The Solar Impulse Prototype HB-SIA has completed a total of four successful flights since April: Each time even longer and higher than the last. The plane’s flight and maneuvering characteristics are being tested and its performance examined, as well as the effect of every fine adjustment to the machine.

At the third test flight, the plane was started for the first time with the cockpit shell. Up until now, this piece had been substituted by a safety cage which was meant to protect the test pilot, Markus Scherdel, from any possible, broken wing parts. Everything was a complete success: the aerodynamics are restored, the wind didn’t warp the cockpit shell and the windshields are staying clear.

The prototype’s next test flights are going to focus on the solar panels. First by day and then by night. Will the around 12,000 photovoltaic cells embedded into the wing of the HB-SIA generate enough energy so that the solar plane can fly through the night, just with the power of the sun? The energy which is collected from the sunlight will be used partly for the immediate propulsion; however a large portion is stored in batteries for the night flight. Within the coming weeks, the two pioneers, Bertrand Piccard and André Borschberg, will take on this huge challenge: The prototype will be the first manned solar plane to fly at night. Another milestone towards a clean future has even been planned for before summer: a 36-hour flight for a complete day-night-day cycle, propelled solely by solar energy.

“We want to show people that handling our resources sustainably is the biggest adventure of our time”, says Solar Impulse initiator Bertrand Piccard. For, “If a plane can fly day and night without fuel, then no one will be able to make us believe anymore that our society can’t also free itself from fossil fuels!”

You can watch the 36-hour flight by live webcast here.