In Brief
The Solar Impulse 2 finally completed its flight across the globe after first taking off in March of 2015. This feat marks the first time a fuel-free plane circumnavigated the globe.

Solar Impulse 2 has finally come full circle after it touched down in Abu Dhabi on Tuesday.

First Solar Plane To Circle The Planet

It is the first fuel-free plane to successfully fly around the earth, which took 42,000km (about 26,000 miles). The solar aircraft left Abu Dhabi in March 2015, being piloted by Bertrand Piccard and was assisted by André Borschberg.

It took the solar plane several months to circle the planet. Perhaps what it lacks in speed is made up in environmental impact and fuel efficiency, since the plane uses only solar power. Its four 17.4-horsepower motors allow the aircraft to hover at around 140km/h (90 mph), and travel at an average speed of 61km/h (38 mph) across the Pacific.

Even the low speeds can be overlooked when its impressive structure is considered. SolarImpulse 2 spans 72m (236 ft), wider than a Boeing 747, but only weighs 2.3 tonnes (~5,000 lbs). Engineers installed 17,000 rigid, photovoltaic panels that charge four batteries, which take up about 35 percent of the plane’s total weight.

Image: SolarImpulse

Not Always Smooth Flying

The Solar Impulse 2 did encountered a few mishaps while circumnavigating the world, like bad weather and fried batteries. Even so, the aviation team was able to raise an extra $20 million from sponsors which allowed the addition of a battery cooling system. Other unfortunate events included a power outage that deflated the plane’s hangar and slightly damaged the aircraft, not to mention Piccard’s upset stomach, which delayed the final leg between Cairo, Egypt, and Abu Dhabi. Finally, scorching temperatures too their toll on the solar plane. The air above the Saudi Arabian desert blazed 48°C (119°F) causing more delays.

In spite of all that, the plane and its pilots soldiered on, and instead used all this extra time cruising the skies to take in some yoga, meditation and 20-minute naps.

Now, who says you can’t sleep while making history? Congratulations to the Solar Impulse team!