The Shape of Wings to Come by Alexis Glynn Latner
You'd be surprised how much you can do without an engine, on Earth and elsewhere! 
* * * *
The year 2003 marked the 100th anniversary of powered flight. Amid the celebrations, there could be detected an undercurrent of regret in the hearts of many aviation buffs, a sense that all the great aviation milestones were history, alas. You can still go a bit higher and a bit faster ... but tweaking existing records doesn't satisfy like carving them out of the air in the first place.
Yet in December of 2003 a sailplane pilot named Klaus Ohlmann won the Kuettner Prize for surpassing 2,000 kilometers in a straight-line flight. The prize had existed unclaimed for twenty years after it was established by Joachim Kuettner, one of the grand old men of aviation meteorology, who set the goal at 2,000 kilometers (about 1,200 miles) because it takes riding a jet stream in the lee of a mountain range for a sailplane to go a great distance in a straight line, but jet streams are only about 1,000 kilometers wide. Someone had to find two jet streams close together. Ohlmann went 2,174 kilometers in thirteen hours above the snow-streaked peaks of quiescent Andean volcanoes. It was silent flight the whole way, no engine, just the whisper of cold air slipping along the smooth, white fuselage of the Nimbus 4DM sailplane.
No more grand aviation milestones?
Sailplanes and aircraft that glide at least some of the time are doing wondrous things lately. In 2004, SpaceShipOne visited and revisited the edge of space, rocketing up past 62.1 miles, or 328,000', then gliding home. It's registered with the Federal Aviation Administration as an experimental glider. Meanwhile the Perlan Project is using sailplanes to explore little-understood stratospheric waves near the North and South Polar ends of the Earth's atmosphere. Sailplanes are sleek vectors into new atmospheric frontiers on this world, and other worlds too.
Before the Beginning 
It all began back when Earth itself was a different world--the world of the supercontinent Pangaea and the flying dinosaurs, the pterosaurs. Pterosaurs could flap their wings, but larger species like Pteranodon must have spent much of their time in gliding mode. It's the most efficient way to fly, and not limited to going down. Air rises under many circumstances. A sufficiently capable flyer can rise with it.
The largest and latest pterosaur was Quetzalcoatlus. This ancient beast had a 40-foot wingspan. That's more wing than the typical Cessna 150. Any flying dinosaur that large had to spend most of its airborne time in gliding mode.
The first bird, Archaeopteryx, dwelled on Jurassic shores and probably did some of both flapping and gliding. What Archaeopteryx probably did not do was crawl up into the trees and learn to fly on the way down. For one thing, there weren't tall trees yet, just ginkgoes and palmlike cycads. For another thing, the most likely outcome of early flights off high perches would be dead proto-birds. The great issue in flight is controlling movement in three dimensions, hard to master in a few seconds of free fall. Archaeopteryx must have done as the pterosaurs did, and young sea birds do now, and it's not a bad way to learn to fly: inhabit a sandy shore with a strong sea breeze, where outstretched wings produce enough lift to glide for short distances, ending at worst in a tumble into the sand. The history of avian evolution is probably not recapitulated in the baby songbird taking the plunge out of the oak tree. The species, if not the baby, long since solved the problem of control. (1)
Ages later came the hawks and vultures. These birds circle on outstretched wings in thermals: air that bubbles up from sun-warmed terrain. If the local air is sinking, raptors flap if they must, but prefer to scrunch their shoulders and make a fast glide to the nearest parcel of air on its way up. Why flap when you can glide over to a good place to soar?
The supreme gliders of nature are the wandering albatrosses. They have long, narrow, pointed wings, which they can lock into the outstretched position. Since they weigh twenty pounds and more, near the theoretical maximum for flying birds of their size, launching entails a long sprint with wings flapping hard. But once aloft, their weight is an asset, because it maximizes the aerodynamic efficiency of their flight. (For things that fly, less weight is generally better: that's why bird bones are hollow and aircraft engines are made out of aluminum. On the other hand, a heavier bird or aircraft will have a higher most efficient speed, allowing it to fly faster and further with minimum expenditure of energy. For that reason, racing sailplanes carry water ballast. It gives them a competitive edge--and they can dump the water if the added weight becomes a liability.)
Wandering albatrosses are old masters of dynamic soaring, an exciting new concept to humans. It means taking energy from the wind to maintain flight. "By heading into the wind and gliding upward from the slow-moving layers of air nearest the sea's surface into faster-moving layers above, the albatross maintains its lift and airspeed without moving a muscle. At the height where the airflow ceases to increase with altitude, the bird changes its strategy. Tracing a ninety-degree arc, it glides back down toward the sea, across the wind, accelerating until, on approaching the wavetops, it once again turns into the wind and uses the wind's energy to climb. The bird can continue this indefinitely, even for days at a time, tacking upwind without ever flapping its wings. Only the most efficient gliding aircraft, with ultralong, narrow wings, can outperform the best albatrosses." (2)
Flying Machines 
Beginning as arboreal mammals whose only flight consisted of jumping from one branch to another, humans are johnny-come-latelies to the sky. But what we lacked in evolutionary focus, we made up for in enthusiasm. We dreamed up legends like Icarus, and we fantasized about flying machines, some of which were actually constructed. Around the year 1000 CE the monk Eilmer glided the length of two football fields before crashing because his contraption lacked a tail to provide lateral stability. (3)
A hundred years ago, the Wright Brothers methodically tackled the problem of aerodynamic control. Experimenting with gliders first, they launched off sand dunes into stiff sea breezes. Not many years later they were flying around the Statue of Liberty in their aeroplane, but they continued gliding too. Orville Wright set a gliding duration record of 9 minutes, 45 seconds, in 1911 in the Wright Glider 5 at Kitty Hawk. (4)
While fervor for powered aircraft seized the human imagination in the early twentieth century, gliders too became more capable, their pilots more canny. Gliders always fall. If, however, you stay in rising air, you can gain altitude. It turns out the world is full of rising air.
At the end of World War I, the victorious Allies prohibited power flying in Germany. So the German government subsidized glider operations in which daring young pilots learned the ways of the sky. Initially they explored how wind interacts with hills and ridges. When wind blows against a ridge, it tends to be deflected up. With a steady wind, skill, and luck, a glider can fly back and forth along a ridgeline. (Illustration 1)
A glider first soared on a thermal in 1926. Conveniently, thermals are often marked by cumulus clouds where the rising bubbles of air reach the altitude where water vapor condenses. Using thermals, the German glider pilots were able to break free of their ridges and strike out across the countryside. They would circle under a cumulous cloud, gaining altitude, and then glide to the next cloud and regain the altitude lost in the glide.
Then the German pilots found a massive atmospheric mechanism that no one had even dreamed existed. Wind blowing over a hill, ridge or mountain range falls downward and bounces back up. It descends again, and bounces up again, and again: a standing wave. Sometimes the wave crests are marked by flying-saucer-like lenticular clouds. (Illustration 2) Joachim Kuettner, then a young German doctoral candidate in meteorology, analyzed mountain waves both theoretically and experimentally. He achieved a world record soaring altitude record of 22,300' in 1937.
Military gliders had a role in WWII. Some transported men and equipment. Others were used in flight training. After the war, Joachim Kuettner relocated to the United States to practice his trade as a meteorologist. He took a leading role in the Sierra Wave Project in the 1950s. East of the crest of the Sierra Nevada Mountains, when winter winds blow from the Pacific, the best wave conditions in North America can be found. Beginning in 1951, civilian pilots and scientists used retired military gliders, outfitted with instruments, to explore the wave with support from the United States Air Force and the University of California at Los Angeles. (Technically there are waves, plural, but in soaring circles it's almost always phrased in the singular: wave.)
Powered airplanes towed the gliders on long ropes, up into a frontier as perilous as it was alluring. High altitudes mean severe cold and little oxygen. Moreover, mountain waves are built around a core of violent wind called a rotor. One Project pilot had his glider destroyed around him by a rotor. He parachuted down with injuries indicating brief exposure to as much as 20 negative and 15 positive g's.
When the glider pilots reached wave conditions and released their tow ropes to fly free, they ascended in smooth, powerful lift. (One pilot who owned a military surplus P-38 flew into the wave, feathered both propellers of the seven-ton warbird, and soared to 30,000'.) The Sierra Wave Project was a tour de force of applied meteorology. Pilots reached altitudes well over 40,000'. Joachim Kuettner demonstrated that it was possible to plan and execute a long cross-country flight in mountain wave. He went 373 straight air miles, using wave over seven successive mountain ranges eastward from Bishop, California. (5)
After 1955, studies of atmospheric wave were taken over by high-flying planes. One of these was, and still is, the U-2, the high-altitude spyplane. U-2s range up to 70,000', where the sky overhead turns midnight blue. The U-2 resembles a cross between an airliner and a sailplane. It is a fragile airplane with long, slender wings for efficient flight. It flies so efficiently that pilots have to deploy high-drag devices to get back down--just like sailplanes which, when descent is called for, open spoilers or air brakes. The glide ratio of the U-2 is 28:1, meaning it can glide 28 miles for every mile of altitude, if, for example, the engines flame out. U-2 pilots have glided as far as 250 miles to a safe "dead stick" landing. (6)
The Space Shuttle is the opposite of the U-2: massive, with short wings and a glide ratio of 4:1, slightly more aerodynamic than a rock. But glide it does. Once the problem of control is solved, you can glide far from high altitudes, even from space, even if you're not optimized to glide. And even if you didn't intend to be a glider! In 1983, an Air Canada Boeing 767 ran out of fuel at 35,000'. The pilot and copilot glided 45 miles to a safe landing on an abandoned Royal Canadian Air Force training field at Gimli, Manitoba. (7)
In general, though, aircraft that glide and soar are built for it, and have a streamlined shape with long, slim, thin wings. It took generations of aviation technology to approximate the wing of the wandering albatross. The problem was developing lightweight materials with enough strength and rigidity to prevent wings from breaking or twisting excessively under their load. At the outset, the limited structural strength of wood dictated thick stubby wings. Fabric stretched across a wooden framework was impossible to shape with great accuracy. Metal was an evolutionary improvement over wood and fabric. But the revolutionary leap came with fiberglass and subsequent composite materials. These are light, strong, and can be shaped with exacting accuracy. Fiber composite wings can be tailored to limit twisting loads, the bane of long, slender wings. Composite materials make all the difference in the world.
It's no surprise that the world's most famous experimental aircraft company is named Scaled Composites. Founded by designer Burt Rutan in 1982, Scaled Composites created Voyager, the first airplane to fly around the world nonstop with no refueling; SpaceShipOne plus mother ship White Knight; and Global Flyer, built for a successful 2005 solo flight around the world by adventurer Steve Fossett. Global Flyer has a jet engine, a lot of long, slim wing, and a glide ratio of 30:1.
The Sky is Not the Limit 
The skins of modern sailplanes are so smooth that even the edges of painted stripes are sanded. State-of-the-art wings exhibit pure aerodynamic form, with winglets and other fantastic curves. Famed German Klaus Holighaus sailplane designer is said to have commented, "If it looks good, it'll fly good too."
Above all, the newest glass wings are l-o-n-g. Longer wings mean better glide ratio. The longest wings of all belong to the giant motorglider called Eta. With two one-behind-the-other seats in a slim fuselage, it has a wingspan of 101'--more than a Boeing 737. Its glide ratio is as high as 70:1. The carbonglass wings are incredibly thin for their size: the cutting edge of sailplane design. When Eta's wings are loaded, they flex, as do all loaded wings (and bridges, and bookshelves) whether the unaided eye can detect it or not. But with Eta, the amount of visible flex makes observers do a doubletake. (Illustration 3)
On the other end of today's sailplane size scale are the new ultralight sailplanes, such as the Sparrowhawk. In this size range, sailplanes can use microlift: updrafts too brief or too slight for heavier sailplanes, but possibly very common in the sky. Eta and Sparrowhawk are both answers to the perennial question of how to stay up longer in less lift. One answer is to have albatross-like wings. The other answer is to be light and nimble enough to use odd bits of lift that until now only the hawks and the vultures could feel. Either way, state-of-the-art soaring machines exist where the cutting edges of materials science, aeronautical engineering, and meteorology intersect, and we are nowhere near the limits of the technology.
As performance improves, the horizons of soaring widen in every way. Ambitious pilots make flights of 1,000 kilometers (621 miles) and more along ridge systems such as the Appalachian Mountains and the island chain of New Zealand. In hotter parts of the world, thermals are powerful and high, and sailplane pilots cover hundreds of miles by climbing as high as 20,000' in a strong thermal and then gliding to another one.
In the lee of winds blowing across the Andes Mountains, great distances can be covered by riding the mountain wave. Shortly before his Kuettner Prize distance, Klaus Ohlmann set an out-and-back record by flying 3,000 km (1863 miles) along the Andes. The straight-line world distance record as of this writing, set by Steve Fossett and Terry Delore in December of 2004 in the Andes, is 2,183 kilometers--as far as the distance from New York to Dallas.
The world altitude record in a sailplane is 49,002', set in 1986 in the Sierra Nevada wave. That record won't last much longer if the Perlan Project succeeds. "Perlan" means "pearl" in Icelandic. Rare, pearly clouds sometimes form at high altitudes and high latitudes, and Perlan, another of Steve Fossett's endeavors, is an attempt to ride mountain wave into the stratosphere. Meteorologists suspect that mountain wave can break through the Earth's tropopause into the stratosphere in a high-altitude, circumpolar ring of winter winds called the polar vortex. The first Perlan flights are being made with a modified production sailplane, a DG 505 motorglider in which the motor has been replaced by batteries and a liquid oxygen system. It's hoped the DG, with pilots in pressure suits, can make it up to 62,000'--U-2 country--exploring the polar vortex. The next step will be to build and design a special, pressurized sailplane to ascend to 100,000' over New Zealand or Patagonia.
On the other side of space, gliding spacecraft may explore Mars someday. With a bit of atmosphere, a lot of wing, and lower gravity, unmanned gliders are a very plausible way to explore Mars. One proposed mission involves unfolding several small instrumented gliders over Mars' huge Valles Marineris canyon to investigate the geology. Elsewhere in the solar system, several moons and worlds have atmospheres. Places where wings would work include Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, plus Saturn's moon Titan and Neptune's moon Triton. Unmanned gliders are conceivable in each of these places.
And buoyancy-driven undersea gliders might work on the Jovian moon Europa. In the oceans of Earth, stubby-winged exploratory gliders dispense with hefty engines, propellers, and many hard-to-maintain moving parts. Instead, battery-powered gliders travel for days on end, making slow but steady progress, pumping seawater in and out to rise and sink down again. Similar technology might work in oceans under the ice of Europa. Instead of shifting water in and out, Europa exploration gliders might shift oil in and out of external sacks to descend and ascend. That trick changes the craft's volume and density, and it sinks or rises accordingly. The idea has the virtue of simplicity--always a good idea when sending machines across the solar system.
Sailors on a Sea of Air 
Many visions of the future suggest the wings of exploration. Duncan Lunan and Gordon Dick considered flight in non-terrestrial atmospheres in a 1993 Analog fact article, citing aeronautics researcher Terence Nonweiler, who advocates winged vehicles for landing on an Earthlike world. Wings give you time to enquire over a landing site. Wings are an elegant alternative to using precious energy to stay aloft by other means. (8)
Far in the future, if and when colonists from Earth settle in on a new world elsewhere in the galaxy, they may have some interesting constraints on fuel choices for aviation or other transportation. Not every Earthlike world will have a trove of fossil fuel. Batteries are heavy. Solar panels mean packing delicate hardware along. Most kinds of fuel mean extra weight, at least as long as you have it, and an emergency the instant you run out.
But there's energy in an atmosphere like Earth's. Lots of energy. As the raptors know so well, if you want to fly efficiently, use the great engine that is the sky. Utilitarian and commercial aviation did not take the raptor route on Earth--fossil fuel being plentiful--but there is no reason why it could not. With the right atmospheric conditions and terrain, plus some relatively modest infrastructure, plus economic factors in its favor, gliding/soaring might be a favored way for human colonists to travel around on another Earthlike world.
This definitely includes personal transportation by means of hang-gliders. Hang-gliders use all kinds of lift, just as sailplanes do, and will excel at using microlift and dynamic lift. And among the many beauties of hang-gliders is the ease of landing. No runway is required.
Sailplanes are a more powerful exploration and transportation tool than hang-gliders, though, and more likely to form a framework for aviation on a new world. Sailplanes can go much faster and higher, and carry more cargo, instruments, and passengers, better protecting everyone and everything from cold and thin air. And in strong lift conditions, strong sink is always a factor. Whatever goes up must come down, and that includes air, and when it goes down, it can do so with a vengeance. A sleek sailplane can hammer though strong sink where a hang-glider would be forced down--not good if the idea is to cross vast badlands in a sky shot through with lift and sink. A sailplane can withstand much more turbulence as well.
Serendipity might come into play. A far-future colony could have even more places than Earth that are perfect for hang-gliding and soaring alike. Ideal conditions would include extensive ridges and good prevailing winds; deserts with strong thermals; and large sectors of mountain wave in the lee of long mountain ranges. Given all that, you could do a lot with engineless aircraft, day and night. In ridge lift and mountain wave, night flight is eminently doable.
By the way, we need not assume tow planes to get off the ground in the first place. Self-launching motor gliders take off on their own and then turn the engine off unless they need it. Some have propellers tucked away in the nose; others have a propeller on a mast that pops out behind the cockpit. (Illustration 4) There is at least one jet sailplane making the rounds at air shows, with twin cola-can-sized jet engines mounted behind the cockpit. Eta and the sailplanes setting records in the Andes are all motorgliders. The motor stays off for the duration of a successful record attempt, but if conditions deteriorate, the motor makes the difference between reaching an Andean airport and landing in a very remote pasture.
And then there is the low tech option for getting up into the air: winches. Ground-based winches, much used in Europe and increasingly common in the United States, reliably fling sailplanes a couple of thousand feet into the air, squarely into an area of ridge lift or a predictable thermal source. Every locality has its stepping-stones into the sky, places where the ridge or the "house thermal" works much of the time. The locals know just where these spots are.
Only a century into mechanized flying on Earth, locals are invariably a smart bunch. Club and competition soaring pilots know how to go cross-country. They understand the way the atmosphere in their part of the world works. The most challenging soaring of all is in the mountains--not just in the wave over the mountains, but the valleys and chasms between peaks and precipices. Such regions have complex patterns of wind, sink and lift, and, in particular, tricky downdrafts that can smash a sailplane against a cliff. Yet local pilots are scouting out reliable aerial pathways through great ranges like the Alps, the Southern Alps of New Zealand, and the Rockies. Colorado pilots can climb into the sky above the Continental Divide.
What if humans explored and soared a new world for generations, a whole world where it made practical and economic sense to soar? In other words, what if a whole human culture really knew how to fly? Modern societies have plenty of airplanes, but few people who understand the air. Even the airline pilots complain about how autopilots and fly-by-wire controls distance the pilot from the sky. Our whole society has a deeply ingrained sense that to go from point A to point B to point C means motoring in a straight line, typically on an interstate freeway.
Travel hasn't always been that way everywhere. The Polynesians, for one example, understood the currents and the winds of the Pacific Ocean well enough to journey thousands of miles to far-flung islands in rafts. Perhaps someday human colonists might have the time and incentive to understand a new world's atmosphere that well: to grow as intimately familiar with their skies as the Polynesians were with the currents of their seas.
In another scenario, the new world would be Earth, older, hotter perhaps, and post one or more cataclysms, with civilization crashed and rebuilt, with no more oil reserves and a sea-changed global economy. A new, old Earth where long-winged gliders climb the sky, brightly-colored hang-gliders cluster in warm regions like butterflies in the sunny spots of a garden, and flocks of ultralight motorgliders crisscross the seas using a cup of fuel and a mastery of dynamic lift, like their fellow travelers, the albatrosses.
Always Another Adventure 
The Morning Glory forms on a sea-breeze front in the Gulf of Carpathia in southern Australia. It's an otherworldly-looking, white roll cloud that stretches from horizon to horizon and moves inland. Soaring flights of three hours and flights of almost two hundred miles have been made on the Morning Glory to date. Earth's atmosphere is full of surprises. And everywhere there is a surprising lift in the air, inquisitive sailplane pilots show up to investigate.
Depending on your point of view, even the local summer thunderstorm is an otherworldly marvel. Cumulonimbus clouds produce powerful updrafts, accounting for some early soaring altitude records (and fatalities). Sailplanes racing in contests sometimes dart under the edges of these storms, venturing into the meshing gears of the atmospheric energy engine in hopes of gaining the advantage to win the race.
Earth's atmosphere is still a strange new world. It may not look that way from the seat of a jetliner streaking through clear air over, say, the rolling hills of Ohio. But there be dragons: the cumulonimbus clouds. And monsters: mountain waves towering over their rotors. And wonders like the Morning Glory.
As a thought experiment, we can well imagine future wings on the intricate winds of new worlds. Remember that almost anything with wings can glide a long way in an emergency, given enough altitude to start with. But long, slim, thin wings are the most efficient. In imagination, we can duplicate some conditions on Earth and extrapolate others. Tweak the parameters of planetary evolution, atmospheric density, and geography: maybe no fossil fuel, but vast hot badlands, long mountain ranges, and an atmosphere with favorable dynamics. It would be especially interesting to posit an otherwise Earthlike world with days and nights longer than Earth's, with more solar heating to generate thermals, and possibly a steeper differential between onshore and offshore temperatures, creating more powerful and perennial coastal winds.
So we can imagine a world where gliders and hang-gliders routinely traverse long ridge lines and coastlines' lengths of sea cliffs. Gliders thread through jagged mountain ranges day and night with only the occasional, much-remarked-upon mishap. Heavier, well-insulated sailplanes routinely launch into atmospheric waves to go high and far. All because people know how to control flight and understand the atmosphere intimately well.
In a different scenario, humans new to a world might ask the intelligent, long-winged natives about the ways of their sky.... But that's yet another story.
Endnotes 
(1) Shipman, Pat, Taking Wing: Archaeopteryx and the Evolution of Bird Flight (Simon and Schuster, 1998).
(2) Furness, Robert W., "Easy Gliders," Natural History, August 1990. p. 62.
(3) White, L., Jr., "Eilmer of Malmesbury, an Eleventh Century Aviator" in Medieval Religion and Technology (University of California Press, 1978), Chapter 4.
(4) Crouch, Tom D., The Bishop's Boys: A Life of Wilbur and Orville Wright (W. W. Norton, 1989).
(5) Whelan, Robert F., Exploring the Monster: Mountain Lee Waves (Wind Canyon Books, 2000).
(6) Pocock, Chris, Dragon Lady: The History of the U-2 Spyplane (Motorbooks International, 1989).
(7) Frazer, Bruce W., "The Gimli Glider," AOPA Pilot, July 2000, p. 74.
(8) Lunan, Duncan and Gordon Dick, "Flight in Non-Terrestrial Atmospheres," Analog, January 1993.
Websites of Interest 
Eta's home page is www. leichtwerk.de/eta/
Morning Glory Cloud page at www.dropbears.com/brough/
Perlan Project page is www. perlanproject.com/Perlan/
Pterosaur Page by the University of California at Berkeley Museum of Paleontology www.ucmp.berkeley.edu/ diapsids/pterosauria.htm
Soaring Society of America Website is www.ssa.org
SpaceShipOne home page at www.scaled.com/projects/tierone/
For grist for the mill of imagination about soaring on other worlds, visit soaring sites on Earth.
Ridge Soaring Gliderport in Julian, Pennsylvania launches sailplanes into ridge lift much of the year. ( www.sac.ca/cas/hangarflying/ridgeprimer/gillespie1.html)
Soar Minden in Nevada regularly takes visitors up to 30,000' on mountain wave capped by lenticular clouds (www.soarminden. com).
Teton Aviation in Driggs, Idaho, offers scenic glider rides up and over the Teton Mountains. (www. tetonaviation.com/soarindex.html.)
Particularly intriguing is Marfa, in West Texas, 30 miles south of the Davis Mountains and McDonald Observatory. Marfa's soaring operation acquaints visitors with thermals up to 18,000'. The area has mountain wave in the early spring, the bones of the pterosaur Quetzelcoatlusin the ground, and some of the continent's best conditions for seeing stars in the night sky. ( www.flygliders.com/marfa.htm) n