On August 7, 1980, Janice Brown flew the solar-powered Gossamer Penguin in full view of a crowd gathered on the Edwards dry lakebed at the NASA Dryden Flight Research Center in California. Janice flew the Penguin almost 3.5 km (two miles) that day in 14 minutes, 21 seconds. This was the first sustained flight of a solar-powered aircraft and the longest Penguin flight since development had started on the aircraft two years earlier. However it was not the first flight on solar power alone. Two months earlier, Penguin designer Paul MacCready’s 13-year-old son, Marshall, had made the first solar-powered flight, a short one of about 152 m (500 ft.), on May 18, 1980. Prior to Marshall’s flight, the Penguin had flown with an on-board battery pack to augment the power provided by the solar cells. This 1979 photo shows Janice flying the Penguin using a combination of solar and battery power:
 

 

A team led by Paul MacCready had built the Penguin to back up the MacCready Gossamer Albatross, which became the first human-powered aircraft to fly across the English Channel in 1979. [Update 8/10/15: the Albatross is on display at the Steven F. Udvar-Hazy Center in Chantilly, Virginia.

 

 

The Penguin spanned 22 m (71 ft.) and weighed 31 kg (68 lbs.) without a pilot. A 3,920-cell solar panel that could be tilted toward the sun produced 541 watts to drive an electric motor called the Astro Cobalt 40, built by AstroFlight Inc.  

The Penguin was so fragile and difficult to control, that flight was limited to the calmest conditions found just after dawn. Unfortunately, the low angle of the morning sun limited the amount of energy falling on the flat wing surface. The development team had to mount the solar cells upright on a tilting panel to keep the cells perpendicular to the sun. The Penguin’s airframe was fragile to keep it lightweight; building the airplane stronger would have made it incapable of flight. The single electric motor could propel only so much weight into the air, and only small pilots could fly the Penguin, which weighed 31 kg (68 lbs.). Janice weighed about 45 kg (100 lbs.) and Marshall just 36 kg (80 lbs.). The Penguin represented a milestone that encouraged others to continue working to increase the structural and aerodynamic efficiency of solar powered aircraft, along with the development of better power systems including lighter weight and more powerful batteries that might one day store the energy from solar cells to enable aircraft to fly even at night. Earlier this year, a workshop on electric propulsion sponsored by the Comparative Aircraft Flight Efficiency (CAFE) Foundation showed how far we have come in the 30 years since Janice flew the Penguin. The future looks very promising. NASA aerospace engineer Mark Moore said last January that "many researchers are proposing a tripling of current battery energy densities in the next five to seven years,” which could lead to small electric-powered airplanes with ranges of 240 to 320 km (150 to 200 miles). Anticipating these improvements, NASA has begun to develop an exciting new concept for an electric aircraft called the Puffin. Please see Scientific American and Alternative Energy News for more information.