Flying as silently as a buzzard, the enormous Solar Impulse 2 took to the skies of Abu Dhabi, United Arab Emirates, in its first operational test flight on Monday, with a goal to become the first aircraft to circumnavigate the planet without using a drop of fuel.
It’s the latest stunt in a long (and distinguished) line: Pilots have circumnavigated the globe in everything from tiny ultralights to 747s. Two aircraft have even flown the span nonstop, an impressive feat of technical and personal endurance (one, the Rutan Voyager, now hangs in the National Air and Space Museum in Washington). But nobody has yet circled the globe as a way to raise awareness of environmental sustainability, which is precisely what the Solar Impulse team has in mind.
Solar Impulse 2 is, as its name implies, the second in the line. The first was flown in fits and starts across the U.S. in 2013, with periodic stops to rest and show off the airplane. This flight will be much the same, on a grander scale. The team plans at least 12 stops around the world, starting westward from Abu Dhabi.
From a practical standpoint Solar Impulse leaves much to be desired, and we shouldn’t expect to be flying electric airplanes anytime soon. Batteries cannot store nearly the amount of energy contained in gasoline, and a roaring giant this isn’t. Solar Impulse uses some of the lightest materials practical, and during daylight is continually re-fueled by solar cells mounted across its entire fuselage and 747-length wing. But it can only lift one person (and the supplies necessary to keep the pilot alive) and it flies at a plodding 77 knots (about 89 miles per hour). The giant wing is necessary both to provide sufficient space for all those solar cells and to generate enough lift while moving so slowly. Flying at typical airliner altitudes would mean less energy required to move through thinner air, but a stiff wind could bring the airplane to a halt, and a strong one would push it backwards. No one will ever look to Solar Impulse 2 for anything other than a demonstration of sun-powered flight.
Still, the project is impressive, and a great step in the right direction. Using batteries at night and charging during the day, it can stay aloft for (as far as anyone can tell) an infinite time; the planned pit stops along the route are mainly so the pilots can rest. Without a pilot those limitations would be lifted, and several companies are experimenting with what are being being called atmospheric satellites, flown with electronic cameras or transmitters instead of a person on board. The goal is to spend as much as five years aloft without landing, flying high enough to avoid most of the bad weather. Rather than carrying airline passengers, these aircraft would compete with space-based satellites, doing essentially the same thing with much less cost and complexity.
You can track the current position of Solar Impulse, or watch a live video feed here: