By Kim Robson:
The Solar Impulse 2 is a solar powered, single pilot airplane currently making aviation and renewable energy history. It recently completed the eighth and longest leg of its record-breaking around-the-world journey, traveling 4,000 miles non stop from Japan to Hawaii without fossil fuel. The plane safely landed on July 3rd at Kalaeloa Airport on the island of Oahu.
The plane took off from Japan after the weather was determined safe enough to attempt the passage. A previous attempt to fly to Hawaii had been made in late May but was aborted mid-flight due to dangerous weather.
The Solar Impulse 2 maintains a slow but steady pace, with a maximum speed of 90 mph and an average speed of 40 mph. At that speed, the leg lasted a marathon 117 hours — nearly five days. In comparison, a Boeing 777, with its top speed of around 600 mph, can make the same trip in only eight and a half hours. The unaccompanied pilot, André Borschberg, had no backup for this leg of the flight, and could sleep only in 20-minute naps the entire time.
With its latest flight, the Solar Impulse 2 broke a number of records, including longest distance for solar-powered flight, longest duration for solar-powered flight, and longest non stop solo pilot flight of any kind.
In a statement, Bertrand Piccard, co-founder of Solar Impulse, said, “This oceanic flight to Hawaii demonstrates that if technological solutions exist to fly a plane day and night without fuel, then there is potential for these same efficient technologies to be used in our daily lives, and to achieve energy savings to reduce CO2 emissions.”
The experimental plane is made primarily of lightweight carbon fiber. The wings have 17,248 solar cells that recharge four lithium polymer batteries, allowing the plane to fly at night. At only 5,070 pounds and with an impressive 236-foot wingspan, Solar Impulse 2 generates enough lift to maintain flight over long periods of time.
The plane, which began its journey from Abu Dhabi, still has five more legs to fly in its groundbreaking journey around the world. The next leg will continue from Hawaii to Phoenix, but not before another delay for repairs.
Watch this video of Solar Impulse Landing in Hawaii:
During the first ascent on day one of the flight from Nagoya to Hawaii, the batteries’ temperature rose dangerously due to the high climb rate and over-insulation of the gondolas. The Mission Team monitored the temperatures very closely during the flight, but there was no way to decrease the temperature for the remaining segment of the leg, as each daily cycle requires an ascent to 28,000 feet and subsequent descent for optimal energy management.
Irreversible damage to certain parts of the batteries will require repairs which will take several months. In order for the Solar Impulse team to repair the overheated batteries damaged during that record-breaking oceanic leg from Nagoya to Hawaii, the airplane will stay in Hawaii with Bertrand Piccard and André Borschberg until early spring 2016.
Overall, the airplane performed very well during the flight. The damage to the batteries is not from a technical failure or a weakness in the technology, but rather an error in evaluation of the mission’s profile and the cooling design specifications of the batteries. The temperature of the batteries in a quick ascent and descent in tropical climates had not been properly anticipated.
In the meantime, the Solar Impulse engineering team will be studying various options for better cooling and heating processes for very long flights. Want to keep track of the latest Solar Impulse news? Sign up on their website to add your voice to the UN Climate Conference in Paris in December 2015, and get a chance to win a trip to Abu Dhabi to see the Solar Impulse touch down at the end of its history-making journey. You can also follow them on Twitter or Google+ and like them on Facebook.