Sun-Powered Plane Aims for New Heights

Back 50 years ago, in the heyday of aviation development, pilots like Chuck Yeager used to talk about pushing the envelope to find where the demon lives.

But in an age when air travel and supersonic flights have become about as common as a hairbrush, that demon--or the point that no man has reached--has become even more elusive.

For a team of engineers and designers at the AeroVironment research facility in Simi Valley, reaching the demon means taking a plane and all of man’s technological know-how literally to the edge of the world.

After more than two years of design and construction, engineers are set to begin testing Centurion--the newest in a line of aircraft designed to fly at the edge of space using only the sun’s energy.

“One of the most exciting things for me is watching a plane take off that you’ve seen go from just a concept to reality,” said William Parks, a senior engineer at AeroVironment who has headed the Centurion project. “But I’ll admit that it always frightens me. . . . I keep wondering if there’s some major design flaw that we’ve overlooked.”

Commissioned by NASA as part of its Environmental Research Aircraft and Sensor Technology, or ERAST, program, Centurion will begin making test flights in October from Edwards Air Force Base--the same base where Yeager was the first to break the sound barrier in the sleek orange plane he affectionately dubbed “Glamorous Glennis.”

However, this time no speed records will be broken and no pilot will be aboard. The feats accomplished will probably impress only those with an affinity for aeronautical engineering.

With its 206-foot wingspan and thousands of coal-gray solar cells, Centurion will fly at speeds under 100 mph but at an altitude as high as 100,000 feet.

It is the latest in a string of solar-powered aircraft that AeroVironment engineers hope will allow them to build planes capable of flying at those altitudes for months at a time.

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“The goal is to get a plane that can fly for a couple of thousand hours,” Parks said. “The technology is pretty much there, but we have some more work to do before we get to that point.”

NASA hopes to use the planes for atmospheric experiments and observations it has unable to perform because of aircraft limitations.

Sampling gases from the upper atmosphere to check for pollutants is currently done using high-flying aircraft such as a U-2 spy plane, but because it flies at such high speeds and for such a limited time, scientists cannot get the kind of data they need to analyze matters from climatic change to ionization above thunderstorms.

The Centurion, however, will give those scientists an ideal way to make those kinds of observations, designers said.

Though the program is geared toward achieving scientific objectives, the aircraft hasmany commercial possibilities as well, said marketing director David Nufer.

The company has been in contact with several communications firms interested in replacing portions of their satellite networks with the planes for a fraction of the cost.

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Where a satellite costs upward of $100 million to design, build and launch, the same equipment could be loaded onto a solar-powered plane and used for as little as $3 million, designers said.

Another benefit, they said, is that equipment on board a solar plane can be upgraded at any time to match the evolving sophistication of modern communications technology.

A satellite, however, generally becomes obsolete in five to 10 years, requiring companies to invest greater sums to maintain their service.

Another benefit, and perhaps the greatest, is that in the event of malfunction in the scientific or communications equipment, the plane can land and the problem corrected. With a satellite, that isn’t so easy.

“If something goes wrong with a satellite or the equipment, well you might as well just wave goodbye,” said senior electronics engineer Earl Cox. “With a plane, a malfunction isn’t that great of a problem; you just land and fix it.”

Other uses, Nufer said, include agricultural monitoring, storm tracking and battlefield surveillance.

There is even talk of one day taking a plane like Centurion to Mars, where it could soar above the red planet, mapping its topography and analyzing its environment for possible colonization in the future.

Despite the prowess and promise of Centurion and predecessors like the Pathfinder Plus, which recently set an altitude record for a propeller plane by reaching 71,000 feet, they are rather gangly contraptions that appear far too fragile to be venturing into the coldest and most inhospitable reaches of the atmosphere.

But its looks are deceiving.

Pieced together from five separate wing sections, Centurion was crafted from carbon composite materials that are lighter than pencil but stronger than steel.

Essentially just one long wing, the plane is designed to carry as much as 1,000 pounds of equipment depending on the altitude. While flying at a lower altitude, the plane can carry more weight, but as it rises and the air becomes thinner, the payload capacity decreases substantially.

Designing a plane that can carry payloads into the atmosphere’s farthest reaches provided some interesting challenges for AeroVironment’s two engineers.

But for the company that designed the human-powered Gossamer-Albatross that crossed the English Channel in the late 1970s and the Sunraycer solar-powered car, challenge feeds its success.

Founded in 1971, AeroVironment has been propelling the development and advancement of highly efficient and environmentally safe machines for government and civilian use.

But since winning the contract to perfect a solar-powered plane, AeroVironment has dedicated most of its research staff to solving the problem of getting a plane to fly 20 miles high for months at a time running only on sunlight.

“The entire plane was designed around power,” Cox said. “We knew how much we’d be able to get, so that was the unbending requirement that forced us to design it the way we have.”

Though the engineers tweaked existing technologies and avionics concepts to design the plane, they were forced to blaze new trails in other areas to get the idea to work.

One of these was to redesign the propellers.

As a plane gains altitude, there is less air to keep it aloft. So as it gets higher, a plane must fly faster.

But with such a finite amount of energy available--about enough to run two dozen hair dryers--engineers had to redesign the propellers to be able to push more air more efficiently.

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What they came up with was a large, football-shaped propeller that has spun off into a ceiling-fan revolution.

“What we found in designing the propellers was that ceiling fans are really not very efficient,” Parks said.

Though engineers have proved that a solar-powered plane can be built and flown at very high altitudes, none has yet made the kinds of long-duration flights NASA and commercial firms require.

And that problem hinges solely on designing an energy storage system capable of operating in the cold, low-pressure environment of the Earth’s upper atmosphere.

“That’s the next challenge for us,” Cox said.

With Centurion ready to begin testing, another plane christened Helios is being built, piece by piece, at the company’s Simi Valley location.

Designers said it will be a more refined version of Centurion that will incorporate newer design ideas that engineers hope to glean from the October tests.

“I do tend to get a little nervous when a plane takes off for the first time, but nothing [disastrous] has ever happened,” said Parks. “But I scare easy.”