Into thin air: Gliding to 90,000 feet

Einar Enevoldson prepares to fly in 2006 (Image: The Perlan Project)

A record-breaking pilot with lofty ambitions aims to fly higher than ever before, and he won't be needing an engine

INSIDE the glider high above the snow-capped Andes of Patagonia, a rush of air blasted from a canister. Einar Enevoldson immediately knew he faced a tough decision.

He was attempting to fly a glider to a record-breaking altitude of 50,000 feet (15,000 metres) and beyond - a feat that most pilots considered impossible. With him in the plane was adventure-seeking billionaire Steve Fossett, who was bankrolling the attempt.

High-pressure air from the canister surged through soft pipes and into Fossett's orange space suit. It ballooned and stiffened. This wasn't supposed to happen at their altitude. If the suit inflated further, Fossett would be immobilised for hours. Worse, his suit could block the controls, making it impossible to land the aircraft safely.

And yet, with the southern winter drawing to a close, this could be their last chance to fly. Enevoldson, who was 74 years old at the time, had spent 15 years working towards this flight, and decades dreaming of it. If they could only get high enough, it would prove his theory that a glider could ride high into the stratosphere. Turn back, and face huge disappointment. Carry on, and it was risky.

That was 2006. Enevoldson and Fossett's flight was part of a bold plan called the Perlan Project. Enevoldson reckons he has found a way to soar higher than anyone had thought possible in a winged craft, by hitching a ride on awesome stratospheric waves powered by the polar vortex. His goal is to fly without fuel or an engine to 90,000 feet, where the Earth's curvature glows against the blackness of space. Up there, the air pressure is less than 1 per cent of the pressure at sea level. That's equivalent to the surface of Mars, and too thin to support the mass of almost any crewed plane. So the Perlan team is building a winged craft unlike any before - a cross between a glider and a space capsule that will be light and fast enough to fly at this extreme altitude. After years of planning, setbacks and tragedy, Enevoldson's Perlan Project is poised to push back the limits of aeronautical exploration.

The official altitude record for a sustained horizontal flight in a piloted aircraft is 73,736 feet, set in a Lockheed U-2 in 1989. Other craft have gone even higher into the stratosphere, but not using wings. Fighter-jet pilots, for example, have used their boosters to propel themselves on a parabolic trajectory to more than 100,000 feet, but their mass quickly brought them back down.

With no heavy engine or fuel, a glider's wings could in principle support it in the stratosphere. The problem is getting up there. For their highest rides, glider pilots search for "mountain waves", which form when a weather front spills over a mountain, creating upward draughts on the lee side. They are signposted by lenticular, or UFO-shaped, clouds formed by the rippling air. But there's a limit to how high these draughts go. Just below the stratosphere, winds tend to change direction or stop altogether, killing any mountain wave. So pilots long assumed that the tropopause - between 33,000 and 49,000 feet (10 and 15 kilometres) - was as high as you could go in a glider.

See graphic: "Surfing the atmosphere" 

World's tallest waves

Enevoldson was convinced that the received wisdom was wrong. And in the early 1990s he happened across a crucial piece of evidence to support his theory. He was in his 50s at the time, with 13 world records to his name accrued during decades as a pilot for the US air force, the UK's Royal Air Force and NASA.

While visiting the Institute for Atmospheric Physics near Munich, Germany, a picture pinned to the wall caught his eye: a pixelated smear of reds and yellows. Pleased by Enevoldson's interest, the lab director explained that it was taken by lidar, a radar mounted on a research plane and pointed upwards at the sky above Sweden's far north. It showed particles rising and falling inside high-altitude pearlescent Arctic clouds. Enevoldson was looking at a stratospheric mountain wave, the same phenomenon that glider pilots had been soaring on for decades in the troposphere, only much taller. At the time, meteorologists were discovering that such waves form at both poles during their respective winters, when cool air sinks towards Earth. As the air descends, the Coriolis effect swings it around and generates a vortex of winds called the polar-night jet, which circle the Arctic and the Antarctic. When these powerful winds meet the Andes, they form the world's tallest mountain waves (see diagram).

And so a decade later, Enevoldson and his financial backer Fossett found themselves high above Argentina searching for a stratospheric ride. Their glider was named Perlan 1, after the picture of pearlescent clouds in Germany. To avoid having to build an expensive pressurised cabin, they had borrowed spacesuits from Enevoldson's old buddies at NASA.

It was the second day in a row that Fossett's suit had malfunctioned. Enevoldson opened the air brakes and tipped the glider's nose toward Earth. Mission aborted.

"Wait a minute," he heard Fossett calling. As they had dropped, he had felt his suit deflate.

"With anybody else I'd go down, but with Steve - Steve was cool," recalls Enevoldson. He told Fossett to keep away from the plane's controls, and up they went again, 33,000 feet, 35,000 feet. But then, no further. Fossett's suit was working properly again, but they had reached a plateau.

Enevoldson ventured in one direction, then in another, feeling the air for a hint of lift. Nothing. He pushed west, over the crest of the Andes.

Far below them, Chilean authorities were putting out puzzled enquiries about the unrecognised craft that was venturing into their airspace. The plane was losing altitude, so they turned back east.

Suddenly, there it was. The unmistakable upwards propulsion of a new wave. Later, GPS and meteorological models would show that Enevoldson had guided Perlan 1 from the crest of one wave to the bottom of a taller adjacent one. The crucial manoeuvre allowed them to burst unequivocally into the stratosphere and set the world record for glider altitude. It also provided the first direct confirmation of meteorological models of stratospheric waves in the southern hemisphere.

By the time they reached 51,000 feet, the pair had been in the air for over 5 hours and cabin temperatures had dropped to -10 °C. They were exhausted, so decided to descend - but tantalisingly, the rising air had shown no sign of stopping.

Before the wheels had touched down, Fossett declared it was time to build a bespoke pressurised plane and fly higher. Next time they would go to 90,000 feet, which would be the highest winged flight ever piloted.

Fossett wouldn't live to see it. Just over a year later, he set off alone at the controls of a single-engine plane from a private airstrip in Nevada, and vanished. Enevoldson was part of the search party that scoured the Sierra Nevadas for the billionaire. Fossett's shattered plane, along with his remains, were not found for nearly 13 months. Enevoldson had lost a friend, a co-pilot and, bluntly, his funding. The Perlan adventure seemed to be over.

To the edge of space

Fast-forward to 2011. Once a month, Enevoldson makes a 9-hour drive north from his home near Berkeley, California, up the foothills of the Cascade mountains and across the elevated plains of southern Oregon, to a small town called Bend. Wooden barns dot irrigated fields interspersed with cattle pastures and pine trees.

His destination is a small, private airfield with five unmarked hangars. Inside, sparks fly, drills screech through metal, burrs carve into styrofoam and workers lay tacky carbon-fibre sheets into moulds. This is Windward Performance. Greg Cole, the company's owner, is an aeronautical engineer, designer, craftsman and above all a perfectionist.

That's why Enevoldson chose him and his team to build Perlan 2: the plane that will take him to 90,000 feet. If the project is Enevoldson's baby, the plane is Cole's. His team is building almost every component, from the fuselage to the 13-metre-long wings. The plane will account for the lion's share of the $2.5-million cash injection that saved the project in 2010. That lifeline came from multimillionaire Dennis Tito - the world's best-known space tourist - who will also get a seat in the plane.

Perlan 2 is a cross between a glider and a space capsule. Its cabin is not only pressurised, it is completely sealed. For safe crewed flight at high altitudes, jet planes pressurise their cabins by constantly sucking in outside air, but with no engine on board, that is not an option for Perlan 2. Instead, it will use compacted air stored in its tail to adjust the pressure in the cabin. The pilots will breathe from a separate tank.

Everything about the wings and fuselage is designed to make Perlan 2 go fast at high altitudes. The higher you climb, the faster you have to go. Fly too slow and not enough air molecules flow around the wings to keep you aloft. But as you fly faster, two factors can create drag on the wings, slowing you down. Each of these problems has been solved in countless plane designs before, but Perlan 2 will be the first to tackle them simultaneously, says aeronautical physicist Mark Drela at the Massachusetts Institute of Technology.

The first is the "Mach number" problem. As a plane approaches the speed of sound, Mach 1, shock waves can form at the rear of its wings where the air flow is fastest - this increases drag. The second, the "Reynolds number" problem, also slows aircraft. The air right up against the surface of a wing is known as the boundary layer. It essentially adds to the wing's shape as it cuts through the surrounding air. Low air density makes that layer thicker, and so enhances drag. This is particularly likely to affect a fast, relatively small plane like Perlan 2, which is 10 metres from nose to tail.

To avoid these problems, Cole came up with a unique wing design. It looks like every other glider wing to the untrained eye, but is subtly different. Its leading edge, for instance, is fatter than a normal glider wing and the tail end of the wing turns down slightly. "It's very subtle but it's actually a significant difference," says Drela. "The Perlan airfoil is similar to something that you would find on a small radio-controlled glider."

Cole's wing could fly on Mars, so it's not out of the question that the design will find its way onto other planes, and even spacecraft.

Whether it is successful on Earth should be revealed later this year, when tests begin in the Californian Sierras. If all goes well, in 2013 Perlan 2 will be packed into a container and shipped off to Buenos Aires, Argentina. From there, the container will head 2700 kilometres south over land, until it reaches the tiny lakeside airport of El Calafate. At the other end of the lake, a glacier sheds its icy load as it emerges from the stony flanks of the Andes.

Enevoldson has assembled a team of eight expert glider pilots, including himself. He anticipates the record will be set in stages, each flight rising a little higher than the previous one, testing the plane as it goes.

To maximise their chances, they are taking meteorologist Elizabeth Austen, from consulting firm Weather Extreme of California. Austen will run forecasts in near-real time. They also hope to collaborate with researchers from institutions including the Naval Research Labs in Monterey, California, and Yale University. Their aim is to study stratospheric mountain waves using lidar, as part of a project called the Southern Andes Antarctic Gravity Wave Initiative.

The hope is that the SAANGRIA research plane will fly in the same airspace, at the same time, providing the latest, most accurate data. In return, the meteorologists are keen for Perlan 2 to collect in situ data at altitudes they cannot reach on their own. They are particularly interested in what happens when atmospheric waves "break", and why it happens. Breaking waves are the principal driver of air movement in the stratosphere, and if weather models do not represent them properly, air flows like the jet stream can start moving in entirely the wrong direction in atmospheric computer simulations. The researchers also want to find out why the region generates more stratospheric waves than anywhere else in the world.

When Perlan 2 lifts off the runway, it will be almost 110 years since the first crewed plane left the ground. In that time, brave pilots have continually pushed back the limits of what we thought possible in an aircraft. Today, there are few places left on Earth where wing-borne planes have not flown, but that's where Perlan 2 is headed.

How will Enevoldson know when it is too risky to carry on? It'll be a buffeting in the wings' tips, a shake in the fuselage - an indication that something in the air has changed. As soon as he steps inside the glider, it becomes an extension of his body. In all his years as a test pilot sending fighter jets into dizzying freefall spins, he was always in control. At some point, Enevoldson will have to turn back. Until that moment, he will keep climbing higher: past the point where the sky above darkens into outer space and the Earth reveals its curve, and into realms that can only be reached by aviation's pioneers.

Catherine Brahic is a news editor at New Scientist

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