Solar Impulse 2, the first solar-powered plane to be able to fly for several days and nights without fuel, is set to embark on its attempt to journey around the world.
The “perpetual endurance” plane was transported to Abu Dhabi in January and will begin its 22,000-mile round-trip in early March, with stopovers in India, Myanmar and China, before crossing the Pacific Ocean and flying across the US and southern Europe, and arriving back in Abu Dhabi by July. It will land 12 times along its route as well as fly non-stop for more than 120 hours – five days and five nights – in order to cross the Pacific and Atlantic legs of its global journey.
Built from carbon fibre, the single-seater aircraft has a 72m wingspan, larger than that of a Boeing 747, and weighs just 2,300kg – equivalent to a standard family car. The 17,000 solar cells built into its fuselage supply the sole power for the four electric motors (17.5hp each) that can take the plane to speeds between 30 and 60mph.
Its technology is modelled on that of its predecessor: Solar Impulse, a pioneering craft that achieved a 26-hour flight in 2010, proving its ability to store enough power in its lithium batteries during the day to keep flying at night.
The masterminds of the project are Bertrand Piccard, the first person to fly around the world in a hot-air balloon, and André Borschberg, a former Swiss air force pilot. The pair will be taking turns to fly Solar Impulse 2, which has been enhanced in three areas compared with its predecessor. These entailed increasing the on-board energy resource, improving its robustness to cope with the extended flying periods and providing a cockpit environment that is tolerable for long distances.
Piccard said: “The plane has, therefore, been developed, to use the project’s own catchphrase, as a ‘flying laboratory’ to utilise a series of state-of-the-art technologies provided by and developed in cooperation with a series of industrial partners.” These have included SunPower for the solar cells and Kokam for the batteries. Specially designed brushless and sensorless 13.5kW electric motors have been made by Etel and turn the 4m diameter propellers at a maximum of 525rpm with an overall system efficiency of 94%.
In addition, they have ensured a more reliable aircraft with redundant safety systems and leak-proof electrical circuits in order to fly in humid conditions. Finally, a form of autopilot, called Stability Augmentation System, will maintain flight altitude and a directional heading so that the pilot will be allowed to rest.
Borschberg said: “Solar Impulse 2 is not about one revolutionary technology. It’s the mix of many solutions, the sum of all the efforts of our engineers supported by our partners that enable us to achieve the impossible.” To overcome the brittle nature and low mechanical resistance of the Solar Impulse solar cells, project partner Solvay, an international chemicals group, conceived a thin fluorine copolymer film to protect them. When the cells are covered with the film, they can be moulded into the wing curvature without breaking. The resin is UV resistant, waterproof and only 17 microns thin.
To ensure visibility when landing after sunset, a lightweight landing system using LED lights was developed by Swiss watchmaking firm Omega. The lights are protected by the same resilient plastic found in Swatch watches. The entire system, including the protective glass, the wiring, power transformer and connector, weighs just under 2kg .
One of the main challenges to overcome will be the pilot’s endurance as they will not be able to sleep over populated areas. Both have developed techniques to relax the body while remaining awake. Piccard uses techniques of self-hypnosis, while Borschberg uses yoga. Above the ocean, sleep will be allowed in the form of short naps of up to 20 minutes 10-12 times a day as the plane will use its autopilot Stability Augmentation System.
In case of emergency, for example if turbulence was to destabilise the plane, vibrating sleeves in the pilot’s suit will alert him immediately, indicating the direction of inclination to correct.
The Solar Impulse team said that the primary purpose of the project is not to revolutionise aviation, but the way in which people think about energy and clean technologies.
Piccard said: “What we are doing with Solar Impulse is clearly demonstrating the effectiveness of technologies that allow us to save energy and produce it from renewable energies. What we use for our airplane, you can also use.
“This is no futuristic or secret technology. No, this is technology that’s accessible to everybody: the same solar panels, the same batteries, the same engines, the same LED headlights, the same construction materials, the same IT programmes. You can also use these in your everyday life for your cars, houses, heating, cooling or lighting systems.”