WASHINGTON : The experimental Solar Impulse aircraft departed Washington early Saturday en route to New York on the final leg of its US tour aimed at showcasing the promise of clean energy, organisers said. The plane, which runs on four electric propellers powered by an array of solar cells mounted on the plane’s 63 meter wingspan, lifted off just before dawn from Washington Dulles International Airport at 0846 GMT. At the controls was Swiss pilot Andre Borschberg, who has taken turns with compatriot Bertrand Piccard on different legs of the flight across the United States.