Solar Impulse is an innovative project leveraging technological prowess and the spirit of adventure by means of an airplane. It was launched in 2003 by a visionary and an entrepreneur, Bertrand Piccard and André Borschberg, challenging common certitudes and making room for a glimpse into a more sustainable future.

The project’s raison d’être is to spread a message by flying in the skies powered solely by solar energy. Having completed its first 26-hour flight through the night in 2010 and the world’s first intercontinental flight connecting Europe to Africa in 2012, Solar Impulse’s HB-SIA prototype is eager to participate in a new challenge: the celebrated coast-to-coast crossing of the United States, San Francisco to Washington D.C. and New York City. Originally unplanned, the perfect opportunity for this new adventure emerged after the decision to rebuild Solar Impulse’s second generation aircraft’s wing spar.

This year’s Across America mission is scheduled to kick-off starting May 1^st, flying from San Francisco to the nation’s Capital and the Big Apple, with 2-3 stopovers on the way. The project’s ultimate goal is to fly around the world in 2015 with the second prototype aircraft, HB-SIB. Eleven percent larger, HB-SIB is designed to cross Oceans and more humid climates from east to west in the northern hemisphere.

Scroll down this Mission 2013: Across America section to get a better overview of the adventure from the onset through our videos, photos and articles!

Just like the eternal to and fro between civil engineers and architects to find the best balance between design and a physically viable structure, a constant discourse goes on between the Design and Structural Analysis teams at Solar Impulse. The difference is that they’re all engineers, so no need to fix wacky structures that can only exist in cartoons.

Everything that’s designed has a purpose but every part needs to fit in the greater scheme of things while also abiding to the strict lightweight guidelines. Led by Geri Piller, the Structural Analysis team consists of 4 engineers. The Design team has the concept, but it’s up to Geri’s team to decide which and how many materials to use for a given part in relation to the load that it must carry.

Geri once gave me a 101 Structural Analysis course (I would have certainly done better at reading a Chinese newspaper though), but I did manage to retain something: every material reacts differently to loads (for example, steel reacts to stress differently than carbon) and this is crucial when building a part.

For reasons of weight, the majority of HB-SIB’s structure is made out of carbon, a very peculiar material. Carbon is extremely resistant in the direction of its fibers, but extremely frail in the other. The Structural Analysis team has to decide in which direction the fibers must be placed, how thick each layer has to be and how many plies are needed. This results in complex manipulations with a specialized software (FEA finite element analysis) where the structural engineers manually input the characteristics they want and subsequently observe how the part reacts to the expected loads applied to it.

It’s not a linear process (it takes two to tango). It’s a constant back and forth between structural and design engineers, an ongoing discussion to reach perfection because, once the design and structure make the perfect match, the part is finally sent to the producer; a joint effort that gives birth to a new part. Because of the unique nature of this aircraft, every part is literally handmade. Consequently, some information can be lost in translation when transforming the software design into a manufactured part. That’s why every part needs to be tested thereafter; a crucial process Geri and his team actively engage in. Stay tuned for information about the Testing team coming soon on our blog!

In the photos: from left to right: Björn Müller, Stefan Pfammatter, Geri Piller and Dominik Dusek (adjacent), Geri Piller (bottom), FEA (top).

Follow the series here: "THE MAKING OF A SOLAR AIRPLANE"