DALLAS, May 23 (Reuters) - A solar airplane that developers hope to eventually pilot around the globe landed safely on Thursday in Texas, completing the second and longest leg of an attempt to fly across the United States powered only by the sun.
The spindly experimental aircraft, dubbed Solar Impulse, touched down at Dallas/Forth Worth International Airport shortly after 1 a.m. local time, logging 18 hours and 21 minutes in the air to cover 823 nautical miles (1,541 km) from Arizona.
The flight set a new absolute world distance record in solar aviation, organizers said.
Solar Impulse, which flies at an average pace of just 43 miles per hour (69 km per hour), began its cross-country sojourn on May 3 with an 18-hour-plus flight from northern California to Phoenix.
After additional stops in St. Louis and Washington, D.C., pausing at each destination to wait for favorable weather, the flight team hopes to conclude the plane's voyage at New York's John F. Kennedy International Airport in early July.
Swiss pilots Bertrand Piccard and Andre Borschberg, the co-founders of the project, are taking turns flying the plane, which has a single-seat cockpit.
Piccard piloted the first leg from California to Arizona, and Borschberg flew the second stretch to Texas.
"This leg was particularly challenging because of fairly strong winds at the landing," Borschberg said in a statement released after the flight. He already held the record for the longest-duration flight in a solar-powered plane - 26 hours.
The Solar Impulse project began in 2003 with a 10-year budget of 90 million euros ($112 million) and has involved engineers from Swiss escalator maker Schindler and research aid from Belgian chemicals group Solvay - backers that want to test new materials and technologies while also gaining brand recognition.
Project organizers say the journey is also intended to boost worldwide support for the adoption of clean-energy technologies.
With the wingspan of a jumbo jet and the same weight as a small car, the Solar Impulse is a test model for a more advanced aircraft the team plans to build to circumnavigate the globe in 2015. The plane made its first intercontinental flight, from Spain to Morocco, last June.
The aircraft runs on about the same power as a motor scooter, propelled by energy collected from 12,000 solar cells built into the wings that simultaneously recharge batteries with a storage capacity equivalent to an electric car.
In that way, the Solar Impulse can fly after dark on solar energy generated during daylight hours. It is the first solar-powered aircraft capable of operating day and night without fuel to attempt a U.S. coast-to-coast flight.
Just as the plane is unlikely to set any speed record, it is also unlikely to set any altitude record. It can climb gradually to 28,000 feet (8,500 meters).
The current plane was designed for flights of up to 24 hours at a time, but the next model will have to allow for up to five days and five nights of flying by one pilot - a feat never yet accomplished.
Meditation and hypnosis were part of the pilots' training to prepare them to fly for extremely long hours without sleep. There is no autopilot mechanism.
The plane's four large batteries, attached to the bottom of the wings along with the aircraft's four propellers, account for a quarter of its overall heft. The lightweight carbon fiber design and wingspan allow the plane to conserve energy but also make it vulnerable to being tipped over.
A ground team of weather specialists, air traffic controllers and engineers track the plane's speed and battery levels and help the pilot steer clear of turbulence. Solar Impulse cannot fly in strong wind, fog, rain or clouds. Its machinery is not even designed to withstand moisture.