Bertrand Piccard is somewhere high over central California right now, flying southward in a giant airplane powered only by the sun.
Piccard is the co-founder and pilot of Solar Impulse, a solar powered airplane that left Moffett Field south of San Francisco shortly after 6 a.m. PDT today to begin an eight-week journey across the country. As impressive as that sounds, it is but a trial run for the dream he and fellow pilot André Borschberg have been working toward since 2007: a zero-emissions flight around the world in 2015.
The longest journey, as they say, begins with the first step, which for Piccard ends after midnight tonight when he touches down in Phoenix. He and his crew have spent several weeks in California, assembling and testing the aircraft after having it flown from Switzerland aboard a Boeing 747.
Piccard is rightfully proud of the airplane, known simply by its Swiss identification number HB-SIA. It is as massive as it is delicate. It’s wingspan of 208 feet rivals that of a 747, yet the plane weighs just 3,547 pounds. It is made almost exclusively of carbon fiber and photovoltaic cells. I caught up with him a few days ago, and he explained with obvious excitement the joy of flying this albatross-like solar-powered airplane.
“It’s amazing to see that really you can do this,” he says as he gently motions his hands up and down as if he were flying. His thumbs and index fingers are pinched together oh-so-slightly, as if holding the thinnest of threads. “You can control it with two fingers, it’s amazing, it’s like a Swiss watch, the precision of the construction.”
That, of course, is what it’s like in calm air. Piccard’s demeanor changes sharply as he describes flying the gentle giant in turbulence.
“When it’s bumpy you have 40 kilos [in your hands],” he says, referring to the 90 or so pounds of force required to move the controls. He gestures with large motions and his hands positioned as if taking a bull by the horns. “You have full deflection [of the controls].”
The overall experience is much like flying a glider. There is a small amount of noise from the motors, and a gentle whistling wind over the cockpit. Though the actual act of flying with the greater proportions has its own set of unique characteristics and the airplane has definite limits with regards to its maneuverability.
Such a craft can be a handful for the most skilled of pilots, including a former Swiss air Force pilot like Borschberg. He has on several occasion flown HB-SIA in conditions that required his full attention.
“You can’t do much else than pilot the airplane,” he says of such situations, “so you try to avoid these very turbulent situations.”
To that end, Solar Impulse has charted a southerly course, both to maximize sunshine and minimize storms. From Phoenix, Piccard will continue on to Dallas. It could be June before he gets there, though. Then he’ll swing north and follow the Mississippi River to St. Louis. The final two stops are Washington, D.C., and New York. No exact dates or specific itinerary have been given, because weather will dictate the pace and route.
Solar Impulse has been flying for more than three years, making increasingly ambitious flights in Europe and Africa and even a 26-hour flight through the night. Borschberg was able to gain altitude and charge his batteries during the day and keep flying while slowly descending during the night.
Its delicate nature aside, the Solar Impulse aircraft has many of the same basic components as a typical airplane. The cockpit is slightly ahead of the wing. Two engines hang from each wing, and at the back you’ll find a horizontal and vertical tail surface. But the plane shares some features with other specialized aircraft. For example, HB-SIA, like the U-2 spy plane, has a single main landing gear.
The general description of how these components work together are familiar to the average pilot, but completely unique in the details.
The biggest difference, of course, is the fuel. HB-SIA is an electric aircraft powered by sunshine. Nearly 12,000 photovoltaic cells cover the upper surfaces of the wings and tail, providing energy for the four, 10-horsepower motors. Excess electricity is stored in a lithium-ion battery so HB-SIA can fly at night. As with electric vehicles, range is paramount. Therefore, the team focused on maximizing efficiency and minimizing weight. So the airplane’s rather simple appearance is driven by function, with several parts serving multiple roles. The tail, for example, carries a non-retractable tailwheel.
“When you make it simple, you make it light,” Borchberg says. “You can put the tailwheel in the structure itself so we save weight and you don’t have to retract it. And it achieves the goal to have the airplane high on the ground to have large propellers.”
Large propellers are more efficient, which explains why they are more than 11 feet long. They spin at 200-400 rpm, keeping the plane cruising at a leisurely 29 mph. Top speed is just over 40 mph. The cross-like tail also distributes the load forces symmetrically. This allowed them to make the fuselage smaller, and therefore lighter, at the tail.
There is room for but a single person aboard HB-SIA, and the cockpit is best described as cozy. HB-SIA uses a traditional yoke rather than a control stick, and all eight ailerons along the 208 foot span can indeed be moved with nothing more than finger tip pressure on the yoke. Moving the controls has a solid, connected feel, without the mushiness often found in airplane controls.
The pilot faces a bank of displays. On the right is a custom-made energy management display that keeps track of the electricity as it flows from solar cells to the motors and batteries. On the left is a radio and GPS unit. In the center is the primary flight display that contains artificial horizon as well as the airspeed indicator and altimeter.
One of the more interesting instruments are two stacks of lights on either side of the primary display. The lights, and instruments that drive them, were developed by Omega and help the pilot precisely control to a single degree the bank angle of the airplane. Unlike conventional airplanes, in which banking the wings 10, 20, or even 30 degrees is normal, the Solar Impulse pilots avoid anything past five degrees to maintain optimal control.
“What is special is this little instrument which gives the degree by degree change, the bank of the airplane,” Borschberg says. “When we have one degree [of bank] to the right, we have one LED. And when we reach five, it starts to blink and it starts to vibrate in the arms.”
Just like many airliners, which have a device called a “stick shaker” to warn of an impending stall, HB-SIA uses a stick shaker to warn the pilot that the airplane is exceeding five degrees of bank.
“The vibration is interesting, because you can be busy doing something else, five degrees is not much,” Borschberg explains, “and at night with no clear references [the stick shaker alerts you] and you immediately have to do something.”
A separate screen that folds down over the right shoulder is a computer interface for electronic communication with the ground as well as a way to view weather, satellite images and other information.
Four power levers situated on the left side of the cockpit control the motors. The pilot usually moves the levers in unison for symmetric control, but there are circumstances in which the pilot will deliver varying levels of power to each of the four motors.
“Sometimes you use differential power not to have differential power, but to equilibrate and balance the batteries,” Piccard explains.
The wings of HB-SIA rise towards the tips, something known as dihedral which aids stability. Because they are angled up, the ends of the wings are exposed to more (or less) sunlight in certain circumstances.
“If you fly for a long time to the south when you have sunrise or sunset,” Piccard says as an example, “you have more electricity on one side than the other because of the dihedral. So you would put more power the side that has the most energy.”
On Monday, I’ll talk more about what HB-SIA is like in the air and, of course, during the all-important landing.Go Back to Top. Skip To: Start of Article.