Sky’s the Limit
Fifty years ago, in the heyday of aviation development, pilots such as Chuck Yeager used to talk about “pushing the envelope.”
These days, a team of engineers and designers in Simi Valley is pushing the envelope by constructing and testing Centurion--the latest in a line of pilotless aircraft designed to fly at the very edge of space using nothing but 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 the AeroVironment research facility, 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 test flights in October from Edwards Air Force Base--the same base where Yeager broke the sound barrier in the sleek orange plane he affectionately dubbed “Glamorous Glennis.”
However, this time no speed records will be broken.
With its 206-foot wingspan and thousands of coal-gray solar cells, the pilotless Centurion will fly at speeds under 100 mph but at an altitude of up to 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.
“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 that the agency is now unable to do because of aircraft limitations.
Sampling gases from the upper atmosphere to check for pollutants is now done using high-flying aircraft like the U-2 spy plane, but because it flies at high speeds and for a limited time, scientists cannot get the kind of data they need to analyze everything from climatic change to ionization above thunderstorms.
A plane like Centurion, however, will give those scientists the ideal way to make those kinds of observations, designers said.
“It’s really the ideal platform to that kind of work,” said David Nufer, marketing director for the Monrovia-based company. “Right now, we’re almost at a point where we meet all those requirements.”
Though the program is geared toward achieving scientific objectives, Nufer added that it has vast commercial possibilities as well.
The company has been in contact with several communications firms that are interested in replacing portions of their satellite networks with the planes at a fraction of the cost.
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.
Another benefit, designers said, is that equipment on board a solar plane can be upgraded to match the ever-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 should any malfunction occur in the scientific or communications equipment, the plane can be landed 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.”
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Other uses, Nufer said, include agricultural monitoring, storm tracking and battlefield surveillance.
Despite the prowess and promise of Centurion and predecessors like the Pathfinder Plus, which recently set an altitude record for a propeller plane after reaching 71,000 feet, they are rather gangly contraptions that appear far too fragile to venture into the coldest and most inhospitable reaches of the atmosphere.
But looks are deceiving.
Pieced together from five separate wing sections, Centurion was crafted from carbon composite materials that while lighter than a pencil are 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 team of two engineers.
But for the company that astounded the world with the human-powered Gossamer-Albatross that crossed the English Channel in the late 1970s and the Sunraycer solar-powered car, challenge is what feeds 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 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 which was to redesign the propellers.
According to Parks, as a plane increases its altitude, there is less air to keep the plane aloft. So as it gets higher, a plane must fly faster.
However, 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.
What they came up with was a large, football-shaped propeller that has since begun revolutionizing the ceiling fan industry.
“What we found in designing the propellers was that ceiling fans are really not very efficient,” Parks said with a chuckle. “It’s one of those spinoff kind of things.”
Though they have proven that a solar-powered plane can be built and flown at very high altitudes, engineers have yet to make the kinds of long-duration flights NASA and commercial firms said they need.
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 slowly being built, piece by piece, in the company’s Simi Valley facility.
Designers said it will be a more refined version of Centurion that will incorporate newer design ideas that engineers hope to learn from the October tests.
“I do tend to get a little nervous when a plane takes off for the first time, but nothing has ever happened,” said Parks, who added that he’s already getting anxious. “But I scare easy.”
