The Stalker demonstration beamed 300 watts of laser power to a solar panel under one wing, with a pointing accuracy of 1 cm at 500 meters, producing enough electrical power to keep the batteries charged. An issue prevented a 48-hr. outdoor flight, but “we had positive power to the vehicle,” says Kare, adding “You still need batteries for takeoff and landing, and interruptions such as satellite passages [as high-power laser are not allowed to be pointed at spacecraft].”
Near-term, and a far cry from its laser-launch ambitions, LaserMotive is focusing on the power-over-fiber market. Able to deliver interference-free power, the technology is expected to find application in laboratories, test environments, telecommunications, and medical systems. The company is developing the system as a lighter alternative to copper wire for powering tethered ground or underwater robots, and is demonstrating the first UAV powered over fiber in the laboratory, Kare says.
For Slovenia's Pipistrel, Green Flight was not the first NASA challenge it won. “We first competed in 2007, in the Personal Air Vehicle [PAV] Challenge, with a prototype we had at the time,” says development engineer Tine Tomazic. “It was a way to have the aircraft independently measured for performance, to see where there was room for improvement.”
NASA provided measuring equipment and know-how. “We could not afford such an elaborate testing set-up ourselves,” he says. Pipistrel's Virus light aircraft won by a considerable margin, although “the competition was not that fierce,” he admits.
Pipistrel returned in 2008 to compete in NASA's General Aviation Technology (GAT) Challenge. “The rules were quite a bit different,” says Tomazic. “In 2007 it mattered to have an aircraft that flew the quickest on the least fuel. In 2008, you had to be very quiet in takeoff and climb.” But the company won again—with the same aircraft.
Green Flight was a combination of the two previous competitions, looking for speed, efficiency, range and low noise. “You had to be able to take off and land in a reasonable distance and fly as slowly as a light sport aircraft [LSA], otherwise the focus was more on efficiency at speed,” says Tomazic.
The rules set a threshold of 200 passenger-mi./gal. to qualify for the prize, or the equivalent in energy for electric propulsion, and the result—perhaps unintended—was that “the designs turned out not to be practical, as we all tried to squeeze out as much efficiency as possible,” he says.
“The rules were drawn up to see aircraft on the flight line that resembled light sport aircraft,” says Tomazic. “And the threshold of 200 passenger-mi./gal. was doable with a LSA with a high aspect-ratio wing, retractable gear and electric power,” he says. “But with $10 million in turnover annually, if we were going to invest $2 million in a competition then we wanted to know we would win.” So Pipistrel set out to “smash” the target.
NASA Langley engineer Mark Moore, who drafted the initial rules that emphasized efficiency and speed, says it was never the agency's objective to create a product for the LSA market. “Certainly our prize partner, the CAFE [Comparative Aircraft Flight Efficiency] Foundation, had this interest,” he says. “As CAFE put their interpretation into the rules, it was clear that their priority was more for near-term LSA market feasibility . . . but the original intent was still present.”