Should the members of the Solar Impulse team realise their 2014 vision of a solar-powered flight around the world, they will have done so in part by standing on the shoulders of giants.
Innovators and aviators have been tinkering with electric-powered aircraft for more than three decades. The first solar-powered craft to fly was the AstroFlight Sunrise, a government-funded, unmanned aeroplane weighing just 12kg that took off from a dry lake bed in California in 1974.
Five years later, the world's first manned solar-powered flight took place using a design modified from a biplane hang-glider. The Solar Riser used the sun to provide electricity to power flights of up to five minutes' duration.
In 1981, the Solar Challenger flew 262km across the English Channel from Paris to London, staying aloft for more than five hours and reaching a then-record altitude of 4,358m for solar-powered flight. Then, in 1990, the Sunseeker flew across the US in 21 stages totalling 121 hours, relying on solar cells on its wings and thermal updrafts.
But, while these efforts helped guide the Solar Impulse team and some of the innovators behind the projects directly consulted with the Swiss team, the organisers often had to come up with their own solutions to design problems.
"All of the previous examples showed that you could fly very well between the hours of 10am in the morning and 3pm in the afternoon. That is when the sun is almost vertically in the sky," says Dr Bertrand Piccard, one of two pilots on the Solar Impulse round-the-world team.
"With these you see the limits of the technology, instead of the potential, he says. "With Solar Impulse, we want to fly day and night."
The design of the first Solar Impulse prototypemeant the aircraft needed to be much lighter proportionally than conventional gliders that had been used previously for solar-powered flights. "Knowing we couldn't use a [glider] manufacturer, we picked out our own team instead," says Andre Borschberg, Dr Piccard's co-pilot.
