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Pushing the limits... No easy task

As we have repeated so often, before every structural test : « If, at 100 % of the intended load, the part breaks, then it must be too fragile; but if it doesn’t break, there’s a good chance it’s too heavy ! ».

This is the philosophy that we have applied since 2007 in optimizing the design of each component. But once the design process was complete, no component has ever again broken … up to now at least… each part proving both strong enough and light enough in weight.

We are always trying to work at the limits of the technologies we are using, and so we have further optimised the design and construction of the airplane’s spinal column, the main wing-spar. A few hours ago, the central section of the main spar of HB-SIB, our second aircraft, failed a torsion test, breaking before it reached the calculated maximum load factor.

It was the very last test, and everyone was getting ready to celebrate passing an important milestone. But the day was to finish in tears and bitter disappointment. More even than for Bertrand and myself, these prototypes are the cherished offspring of the engineers who did the calculations, designed and built them.

This is a major set-back – in fact the first since the Solar Impulse program was launched in 2003. We don’t yet know exactly what happened, what the explanation for the failure is, nor whether it will cause delays to the future operational timetable. The specialists will now have to start examining the matter, but I wanted to make you aware of it immediately.

As we have repeated so often, before every structural test : « If, at 100 % of the intended load, the part breaks, then ...



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