Sunrise, the world's first solar-powered airplane

The design, construction, and flight tests of the world's first solar-powered airplanes, Sunrise I and Sunrise II, are discussed. Sunrise I made its first solar flight on November 4,1974, and demonstrated for the first time that an airplane could fly on solar power alone. Sunrise I made scores of flights during the winter of 1974 and spring of 1975, finally being damaged in a windstorm. An improved version, Sunrise II, constructed in the summer of 1975, first flew on September 12. Sunrise II was 13% lighter, was aerodynamical!} cleaner, and had 33% more power than Sunrise I. Sunrise II was prepared for a high-altitude attempt to 50,000 ft on September 27, 1975. The aircraft climbed at a rate of 8,000 ft/h and was expected to reach 50,000 ft in 6 h. At an altitude of 17,200 ft, the command and control system failed, the aircraft was severely damaged, and the flight test program was terminated.