Stuttgart aeronautical engineer Rudolf Voit-Nitschmann had simply planned an experimental flight. The hobby pilot climbed into his solar-paneled plane one day last summer, with the idea of flying around southwest Germany for an hour or two to test new electronic equipment.

But what started off as a routine test became a world record event.

The Stuttgart University professor steered his glider, the ICARE II, northwards. Five hours later, he landed at Jena, in the German state of Thuringia. He’d flown a distance of some 220 miles -- much further than anyone else had previously flown a solar-powered plane.

“I was a little bit surprised after one-and-a-half hours, after two hours, that the system still worked very well,” Voit-Nitschmann recalls. “So I decided to fly as long as possible.”

A unique aircraft -- with limitations

The ICARE II aircraft looks more or less like a standard glider. It weighs just 640 pounds -- no more than the weight of three sizeable people. Its wingspan measures around 80 feet.

But its most notable feature is a black film of solar fuel cells covering the wings. The energy of the sun, collected in these solar cells, drives a propeller fitted into the tailfin of the plane.

However, there are limitations to solar flying. These planes only really work in good weather conditions during daylight hours -- and even then, only during the warmest six or seven months of the year, when the sun shines for longer periods.

Despite these restrictions, Voit-Nitschmann, who heads a team of 35 aircraft engineers and students, sees a number of possibilities for solar flight. “It will be possible in the future in private transportation, for example sports flying, with one or two persons,” he says, adding that this would result in more environmentally-friendly private flying.

“The second idea is to build commercially operated platforms flying at very high altitudes of about 50,000 feet,” Voit-Nitschmann says. These could provide telecommunications and observations on the weather and other traffic. “They can do nearly the same things with satellites today.”

Waking new interest

One of the consequences of Voit-Nitschmann’s record flight is that it has promoted new interest in solar flying. The Paris-based World Air Sports Federation is now developing special categories for solar flying records. Voit-Nitschmann’s record is not actually official, though, because there’s simply no formal category for solar flight.

“I was also involved in this discussion about defining a category, and I think in one or two years, it will be possible to have an appropriate one,” he says. And when that happens, Voit-Nitschmann will bring out his plane again. “Of course, I will try to establish this record officially if we have the appropriate category.”

If solar-powered flying does catch on in the future as a relatively cheap, environmentally-friendly, and popular form of flying, it will be thanks to the experimental and practical flying work of pioneer aviators like Voit-Nitschmann and his team.