Science: Icarus Would Have Loved It

A 217-lb. plane conquers the English Channel with solar power

Looking like a youngster’s stick-and-rubber-band model, the oddly shaped plane headed slowly down the runway at the small airport near Cormeilles-en-Vexin, a village 25 miles northwest of Paris. It rose only about 50 ft. before sinking haplessly back to the ground. Five more times it tried to fly. On its seventh attempt it was able to get enough lift to make one complete turn before landing again. Finally, on the eighth, it began to rise, climbing in gently looping circles, like a hawk riding an updraft of warm air, to an altitude of about 250 ft. “O.K., you guys,” radioed Pilot Stephen Ptacek, 28, to a control team on the ground. “I suggest you get the cars ready to leave.”

With that, the Solar Challenger continued its climb to 2,000 ft. and headed northwest toward the English Channel. Five hours and 23 minutes later, after a flight of 230 miles at speeds no more than 47 m.p.h., Ptacek touched down at Manston Royal Air Force Base on the southeastern coast of England some 20 miles north of Dover. His odyssey might have made Icarus drop with envy. In a historic feat, Challenger had managed to cross the Channel powered only by the glinting rays of the sun.

The flight was one more coup for Challenger’s designer, Paul MacCready, 55, of Pasadena, Calif. Four years ago, the innovative aeronautical engineer achieved an aviation milestone when another of his diaphanous, lightweight craft, the Gossamer Condor, became the first plane to complete a 1.15-mile, figure-eight course on human power alone (generated by a bicycle-like set of pedals). Two years later MacCready’s Gossamer Albatross made the first such muscle-powered crossing over the English Channel.

Prior to last week’s triumph, other planes had flown on sun-generated electricity. But until MacCready, energy was stored in batteries. By contrast, Challenger draws its electricity directly from 16,128 solar cells spread over the top of its 47-ft.-long wings and 13-ft. horizontal stabilizer. The cells, originally designed for Air Force satellites, were borrowed from NASA. (Their cost, if MacCready had had to buy them: at least $130,000.) During the flight, they produced a maximum of 2,700 watts of power, less than 4 h.p.; that is roughly one-thirtieth the power of a small, gasoline-driven aircraft. But it was more than enough to drive Challenger’s two beer-can-size electric motors, mounted directly behind its big prop.

Made largely of tough lightweight plastics —Kevlar fiber struts, Mylar sheathing, a Lucite windscreen, all from the project’s sponsor, Du Pont—Challenger weighs only 217 lbs., excluding Ptacek, who had managed to diet down to 122 lbs.

For a while, it looked as if MacCready’s plastic bird might never leave its nest. Since arriving in France in early June, he and his colleagues had played a frustrating game of hide-and-seek with the sun, made one false start and even sought more favorable conditions by packing up and shifting their base to England before returning to France. When Ptacek, who honed his flying skills as a crop duster, finally got under way last week and started climbing to his cruising altitude of 11,000 ft., he radioed that he was being buffeted by turbulence from a passing passenger aircraft. Then a helicopter and a small plane, both apparently filled with photographers, began jostling him as well. He warned he would have to land. Just in time, Ptacek’s colleagues—following by car from Cormeilles to the coast, and in a chase plane with MacCready on board—managed to get rid of the troublesome aircraft with the help of French air controllers, who threatened to revoke the pilots’ licenses.

The actual Channel crossing lasted only 1 hr. 25 min.

But Ptacek kept Challenger airborne an extra 23 minutes to let photographers land first, be cleared by startled customs agents, and get into position to record what turned out to be a perfect landing. Ptacek, gorging on chocolate mousse from R.A.F. chefs, said: “It was a real experience for someone like me who had never been to Europe.” MacCready, joining the celebration with pilot and crew, conceded that “flying an airplane with solar cells is just about the most ridiculous use for solar energy that I can think of.” Nonetheless, he insisted that the flight (total cost: more than $725,000) was not midsummer madness but the best way he knew to show the potential of solar power as an energy source. Not that he has given up on conventional energy. His next goal, he says, is to promote a lightweight, two-seat plane with a gasoline engine so efficient that it can fly round the world nonstop without refueling. — By Frederic Golden. Reported by Ken Banta/London and William Dowell/Paris