Above: Solar Impulse 2 returns to Abu Dhabi at the end of her circumnavigation. While the wings curve elegantly in flight it is on the ground that many of the strains on the aircraft are at their highest. This was the first solar-powered aircraft of any range that could lift off under its own power – previous craft were dropped from aircraft or launched off special tracks. After building both America’s Cup and Whitbread winners, the Solar Impulse builds (left) took the Décision team up to whole new strata of detail perfection and super-critical weight management… The company’s next marine project – the Groupama AC50 – was a walk in the park
the Swiss team that had created the black sail construction for Alinghi (which later became 3Di) who we already knew well. ‘For our purposes we suggested they try
changing their (soft) resin system to achieve a harder laminate. We made the first tests of this new epoxy resin system using their technology; what we ended up with formed the foundations of the 3Di and TPT technology that they later devel- oped with the North Group. ‘They would computer-generate the
skin shapes and cut them on a plotter which was fed by a 1m diameter roll of super-thin fibres. At the time this was completely new technology; we were now working from pre-pregs that weighed barely 25g/m2
. So with 10 layers you could
go to 250g/m2 and then flow smoothly back down to 25g/m2 with near-perfect
laminate continuity; the interim steps are now so tiny that you can all but eliminate the risk of localised stress points. ‘This also means we could save signifi-
cant amounts of weight that would other- wise be needed to reinforce locally to address these concentrations.’ So how difficult was it to approach such
a large structure with these difficult-to- handle super-light materials? ‘It’s very difficult. The sheet of paper you use in the office is perhaps 80g and we are building a
38 SEAHORSE
very large aircraft using 25g material. ‘By the end we had a big range of tricks
to deal with it. Sometimes removing the backing paper (which is of course much heavier than the carbon), sometimes using a different delivery system, sometimes effectively no delivery system. Many, many tricks!’ But all these new ‘tricks’ meant it was
crucial that manufacture was very close to the facility where they cut the carbon fibres on the plotter. So Carboman Group in Vannes acquired their own plotter, since used to create wing components for Airbus Industrie as well as most of the Groupama ACC catamaran. ‘It’s quite funny,’ says Cardis. ‘It all
started with the black sails for Alinghi’s Cup campaign in IACC boats in Valencia in 2007, then Solar Impulse 1 and then the technology was properly developed for Solar Impulse 2. Now it has gone full circle and has been used to build the latest America’s Cup catamarans. As far as we know all the 2017 Cup teams were employing TPT in some way. ‘In fact, there was no other alternative
but to use TPT at the time,’ says Cardis. ‘There was little if anything as light avail- able on the market in 2008 when we began manufacturing. Today different alterna- tives are appearing – I see some Swedish
guys are now developing some very light products. It’s coming on the market, but back in 2007-2008 it was really the only solution in the world that delivered such light carbon solutions.’ But this was an expensive way to buy
carbon… ‘Very expensive!’ says Cardis. ‘Today the price is coming down but it was expensive then partly because, though it was a really strong product, it was still very much in development and did not work every time – quite often we needed to make the same piece twice. It was not an easy solution but we knew it had the potential to give us the lightest airframe.’ Cardis says he is still often asked
whether the weight-saving technology used for Solar Impulse could create similar dramatic savings for yachts. ‘Not really, it all depends on the load,’ he explains. ‘We did use a lot of the same technology for the two C-Class cats we built for the Hydros Little America’s Cup team. ‘We could save quite a lot, but it’s an
extreme example because the C-Class is really a small boat. Similarly you could save weight on a Moth, for example. But not on a sailing boat with bigger and more unpredictable loads, it is not sensible. ‘Both the Hydros C-Class boats were
built 100 per cent with TPT. But the really interesting part of that project is that we
w
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