Solar Impulse 2 is much more than an airplane. The solar-powered marvel is, essentially, a flying materials lab. It’s also an engineering and innovation showcase. And, in the eyes of its visionary creator, it aspires to be both a beacon of sustainability and an inspirational symbol of the promise of renewable energy.
Late on May 21, this single-seater plane, made mostly of carbon fiber composites, arrived in Dayton, Ohio, after an 18-hour flight from Tulsa, Okla. Late on May 25 it arrived in Lehigh Valley, Pa., after a nearly 17-hour flight. Next stop is John F. Kennedy International Airport in New York, before embarking for Abu Dhabi in the United Arab Emirates, on the final legs of its round-the-world mission, which started in March 2015.
The Solar Impulse 2
Solar Impulse began 17 years ago as a dream of Bertrand Piccard, a Swiss pilot, psychiatrist and adventurer who wanted to showcase the possibilities of renewable energy.
Piccard went to all the major aircraft makers to seek their involvement in building an unbelievably lightweight, entirely solar-powered plane. They all declined or said it couldn’t be done. But Piccard kept searching. Eventually he found an unlikely but willing partner – Swiss boat builder Décision SA. A specialist in polymer-matrix composites, Décision developed a honeycomb structure, sandwiched between layers of carbon fiber, that encapsulates the photovoltaic cells.
In 2003, Piccard – who is now 58, chairman of Solar Impulse and still flying – connected with André Borschberg, a mechanical and thermodynamics engineer, entrepreneur and pilot who had flown fighter jets for the Swiss Air Force. Four years of research and two years of construction followed, with the first Solar Impulse plane, known as HB-SIA, making its maiden voyage in December 2009.
Borschberg – the project’s co-founder and CEO – flew the Si1 prototype for more than 26 hours in July 2010. He rose above 27,000 feet and recorded the first solar-powered night flight. That original Solar Impulse plane holds eight world records. But that was just the start.
The team took what it learned and developed Solar Impulse 2 (Si2), a lighter-weight, more advanced version of the plane. Unveiled in April 2014, Si2 consists largely of carbon fiber, has a wingspan of 72 meters (or 236 feet – longer than that of a 747), yet weighs only 2,300 kilograms (or 5,100 pounds – about as much as an SUV). It is 25 meters (82 feet) long, and has 17,248 photovoltaic cells built into the wings that supply four electric motors with renewable energy. The solar cells recharge four lithium polymer batteries.
These allow the aircraft – which travels at a speed of 30-60 mph – to fly at night and have virtually unlimited autonomy. When it flies, the Solar Impulse follows a pattern of soaring to 28,000 feet (8,534 meters) during the day, then using battery power as it glides down to lower elevations at slower speeds for much of the night. Last year it flew nonstop – at an average ground speed of 61 km/h (38 mph) – for five days and nights, on its record-shattering trip from Japan to Hawaii.
SolarImpulse.com lists almost 50 partners in this very international project. Belgian materials supplier Solvay Specialty Polymers became a partner back in 2004. Germany’s Covestro LLC has developed numerous materials for Si2. Swiss watchmaker Omega developed the low-energy instruments on board. Swedish engineering giant ABB and the Swiss elevator maker Schindler are key contributors. At various stages, the team has sourced honeycomb materials from Germany, carbon fiber from Japan, lithium polymer batteries from South Korea, and photovoltaic cells from California.
Fifteen Solvay products are found in more than 6,000 components of Si2, including lightweight, high-strength plastics, films, fibers, lubricants and coatings. Its Halar ECTFE fluorinated film, for example, provides a transparent, protective covering for the plane’s solar cells.
And Solvay’s Emana polyamide-based smart yarn, coupled with a far infrared technology, is used in the pilot’s flight suits. The material absorbs human body heat and re-emits it through the interaction of infrared waves with the body. This serves to reduce muscle fatigue and enhance muscle recovery thanks to bioactive minerals that stimulate the blood micro-circulation.
Covestro, meanwhile, first engaged with Solar Impulse in 2010, back when it was still known as the Bayer MaterialScience unit of Germany chemicals giant Bayer AG. The unit spun off and rebranded itself last year.
Si2 charged Covestro with designing and building the plane’s cockpit. This was no easy task, given that the temperature outside the plane can hit – 40 degrees C and the pilots cannot afford to expend any energy on heating (or cooling) the cockpit. This structure needs to keep the single pilot safe and comfortable for up to several days at a time.
Over the past six years, Covestro has developed and provided Si2 with various products that significantly reduce the weight of the plane, and play a number of other key roles:
- The multilayer polycarbonate windscreen provides scratch-resistant and impact-resistant, glass-like performance, plus thermal insulation, all at a fraction of the weight of glass.
- Polyurethane-based coatings and adhesives provide durability on the wings’ surfaces and give them their beautiful and distinguishing silver finish.
- Covestro’s highly insulative polyurethane foam encapsulates the cockpit, provides structure and, as noted, keeps the pilot safe in extreme temperatures. The material used for the cockpit insulation saves 70 times more energy during its lifetime than is used to make it.
- The firm developed an insulating material called Microcell to use in Si2’s cockpit door. Yet to be launched in North America, Microcell is a polyurethane rigid foam with a 40% smaller cell size that reduces thermal conductivity by up to 10%. Si2 represents the first-ever use of this material, but there already are plans to use Microcell for cold-chain storage and in the next generation of refrigerators.
Last summer, Si2 pushed the limits of its batteries too far during the record-breaking, five-day flight from Japan to Hawaii. On that leg, Borschberg flew nearly 4,500 miles in 118 hours, using nothing but the power of the sun. But after an initial high climb overheated the batteries, they had no way to bring the temperature back down during the rest of the long trip. The plane landed safely but the damaged batteries had to be replaced, and the team worked to design a better cooling and insulation system. This grounded Si2 for nine months, till it was able to take off again on April 21 for its 2½-day flight San Francisco.
It then flew to Phoenix, went on to Tulsa, Okla., to Dayton (home of the aviation pioneers the Wright brothers). After the plane spent several days on the ground in eastern Pennsylvania, the Si2 team is hoping weather patterns will allow it take off from Lehigh Valley for JFK Airport in early June. [Note: This author, meanwhile, plans to attend and address a reception for product designers at Si2’s inflatable JFK hangar in New York – shortly after it finally arrives.]
Si2 will stay a few days in New York before heading off to complete the first-ever, manned, solar-powered, round-the-world flight, with the help of numerous innovative, lightweight polymer technologies.
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EDITOR’S NOTE: In addition to being able to track the plane’s progress and sign up for daily updates on the Solar Impulse website, those wanting more information may also find these posts interesting: The Swiss Broadcasting Service in mid-April published 10 FAQs about the project, and Covestro marketing communications official John Skabardonis contributed this LinkedIn post titled “What’s all the fuss about Si2?”
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