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Solar Impulse HB-SIB has a new wing spar

News International-French

29 Jul 2013

Decision, the key supplier of Solar Impulse large carbon parts, announces that the second airplane's new wing spar is completed.

In July 2012, during the final structural test of the wing spar, the central part succumbed to the load and broke. This was a vivid reminder that pushing the limits is no easy task and that sometimes, when you’re right on that thin border, you may fall overboard. However, what might have been dramatic in July last year has become an advantage today; the construction delay of HB-SIB brought many new and exciting opportunities such as this year’s Across America mission.

The wing spar is pretty much the solar airplane’s backbone and most important part. It’s the central structure of the wings and, in Solar Impulse’s second generation airplane, it is much larger for a plane meant to fly faster. Consequently, the wings will be subject to more loads by a factor of two. During last year’s failure only the central part of the spar broke and, after thorough testing, the two outer sections of the spar were spared. Nevertheless, the entire spar was rebuilt for consistency reasons, a process that took 10 months, as the design and the production process have since improved. The leftover outboard sections will be kept as a backup.

The wing spar looks like a long rectangular box. It’s fully made out of carbon and it’s glued – or bonded, as the engineers say - together via a very special chemical process, including 20 curing cycles, in a gigantic oven. It takes 64 minutes to bond the parts together and 88 minutes total for the final bracing and cleaning. These time limits must be strictly respected to avoid an uneven process, which can be fatal for the structural integrity of the entire wing spar.

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