Now: solar-powered Gossamer Albatross

Sun power is preparing for takeoff. The world's first piloted airplane flight fueled only by the sun's rays is scheduled to make a short, 15-m.p.h. jaunt this month.

And by this fall, Dr. Paul MacCready -- who was also responsible for the first human-powered flight across the English channel last year -- plans to have finished a solar-powered plane which will be flown 100 miles, from San Diego to Los Angeles.

Aviation, however, is not exactly on the brink of a solar age. In fact, Dr. MacCready explains, his planes are not expected to open new vistas in either commercial or recreational flight.

Instead, he says, he hopes his sunpowered flights will focus attention on development of alternative energy sources, and one source in particular: photovoltaic cells.

Like many scientists, Dr. MacCready says he believes that if there is a future in solar energy as an inexpensive fuel it will be in photovoltaic cells. The cells, which convert sunlight into electricity, are too costly for widespread use now.

But with continued development, which Dr. MacCready hopes to speed by increasing public awareness of solar-cell potential, researchers predict that within another 5-to-10 years photovoltaic cells may become one of the cheapest alternative energy sources available.

The cells -- paper-thin and about as large as a microscope slide -- are the key to the flights of both the Goassamer Penguin, which will be flown as soon as the weather conditions are right, and the Solar Challenger, which is still being built.

The Penguin, which will fly 10 to 15 feet above the ground, will be powered by 2,800 solar cells lined along what looks like a small billboard percehd on top of the plane. Electricity converted by the cells will run a tiny motor which turns the plane's rearmounted propeller.

The Challenger, on the other hand, will be capable of soaring as high 10,000 feet at a speed of up to 40 m.p.h. Sponsored by E. I. du Pont de Nemours & Co., the plane is expected to cost about $320,000, $40,000 of which will be spent on 18,000 photovoltaic cells that will cover the 42-foot span of the plane's wings.

Both planes are extremely lightweight (the Penguin weighs only 68 pounds) and will be flown by a 100-pound woman pilot. If the 100-mile Challenger flight is successful, Dr. MacCready hopes to send it across the English Channel in 1981. But only because he wants to drive his point home.

"A solar-powered plane is no more practical than a man-powered plane," explains Dr. MacCready, who with his team won a $210,000 prize last summer for achievements in human-powered flight. "It was a nice challenge, but it's hard to get enthused about the future of man-powered flight.

"The reason we're building the Challenger," he says, "is to show that you can use solar power for much bigger uses than simply running a radio set. . . . I felt that a long-distance flight with the Solar Challenger would focus public attention on solar cells, and help stimulate the public awareness and support which would speed their development and utilization."

Although the Gossamer Penguin marks the first manned solar-powered flight, the US Air Force experimented with remote-controlled solar-powered flights in 1974 and 1975, in what were then classified projects.

There will be no batteries to store energy on either of the MacCready flights -- a fact which prompts the inevitable question, "What happens when the sun doesn't shine?"

No problem, Dr. MacCready says. Because the Solar Challenger is actually a glider, all the pilot has to do is glide back down to earth.