As an Air Force test pilot, Lt. Col. Dawn Dunlop has flown dozens of different airplanes, from the nimble F-15E Strike Eagle fighter to the massive C-17 transport jet to the Russian MIG-21. Stationed at Edwards Air Force Base, she’s part of the elite squadron that is putting the cutting-edge F/A-22 Raptor, a jet fighter, through its paces. But the aircraft that Dunlop has had the toughest time controlling was a replica of the Wright brothers’ 1902 glider. More than once she crash-landed the muslin-skinned craft onto the windswept sands of Kitty Hawk, North Carolina. “It was a real eye-opener,” Dunlop recalls of the (bruising) experience last year, part of a commemorative Air Force program. “They’ve made it so simple to fly today we’ve forgotten how difficult it was back then.”

This month, much of the world will be revisiting “back then” as numerous ceremonies, books and reenactments mark the invention of powered flight. It was just after 10:30 in the morning on December 17, 1903, when Orville Wright, an Ohio inventor and bicycle shop owner, took off into a near-freezing head wind for a 12-second propeller-driven trip—a 120-foot voyage that may well have launched the modern age. “Aviation is the definitive technology of the 20th century,” says Tom Crouch, senior curator of aeronautics at the Smithsonian National Air and Space Museum (NASM) and author of Wings: AHistory of Aviation, from Kites to the Space Age. “Flight symbolized our deepest aspirations, like freedom and control of our destiny.”

Amid all the celebrations of the long-anticipated centennial, it might be easy to lose sight of just how amazing those landmark early flights were. As Dunlop discovered, Wright aircraft were dangerous. Frail assemblies of wire, wood and cloth powered by homemade engines, they were reluctant birds, difficult to steer and easy to crash. In fact, planes based on the Flyer that Orville Wright coaxed off the ground would kill dozens of pilots in coming years. Still, the craft embodied what we recognize today as the basics of flight, and though aviation has advanced far beyond anything the brothers might have first imagined—in 2000, airplanes carried more than three billion passengers—the Wrights anticipated a surprising range of crucial developments. “Flying that glider was a real challenge,” Dunlop says, “but when you take yourself back, you realize what a brilliant design it really was.”

From the ancient Greeks, whose mythological tale of Icarus’ wax wings melting when he soared too close to the sun, to carvings left by the South American Incan civilization on the walls of its holy Andean citadel of Machu Picchu, humanity has long been fascinated by the idea of flying. Renaissance paintings and frescoes of Christ’s ascension into heaven “had a concept of air as a thing to be worked,” says Richard Hallion, a former NASM curator and Air Force historian, and author of Taking Flight: Inventing the Aerial Age from Antiquity through the First World War. “Christ is shown lifting off like a rocket, and the Apostles all have windblown garments. Angels have muscular wings in proportion to their size.” Among the most startling early visions of powered human flight are Leonardo da Vinci’s 15th-century sketches of mechanical flapping wings and crude helicopters. Yet Leonardo’s ideas never got off the page.

The first person to apply scientific principles to the problems of flight was George Cayley, an English baronet known today as the father of aerial navigation. Born in 1773, he built the first glider to go aloft with a person aboard—his coachman, in 1853—and correctly identified lift, drag and thrust as the main forces to be mastered for powered flight. Cayley, who published his research in the likes of Nicholson’s Journal of Natural Philosophy, Chemistry, and the Arts, was the first aviation experimenter to use research methods that would be familiar to today’s scientists and engineers, Peter Jakab, chairman of NASM’s aeronautics division, writes in his book Visions of a Flying Machine.

The first hot-air balloon with passengers took to the air in 1783, when its inventors, the Montgolfier brothers, sent a sheep, a rooster and a duck soaring for eight minutes in the sky over Versailles. For the next century, lighter-than-air balloons and airships, unwieldy or impossible to control, were considered the only realistic way to get aloft. Meanwhile, inventors kept struggling with the challenge of powered, heavier- than-air flight. Some built gliders shaped like moths or bats; others built massive, steam-powered aircraft that were unflyable; one such contraption collapsed under its own weight. None “had the slightest influence on the invention of the airplane,” Crouch writes.

Some pioneers were on the right track. The German Otto Lilienthal built 16 different gliders between 1891 and 1896, making almost 2,000 flights in the low hills outside Berlin. In his experiments, he accumulated data on lift and would inspire the Wright brothers, but his death in 1896 in one of his own gliders had a dampening effect on aviation. Convinced that powered flight was a dangerous folly, many Europeans working on the problem aborted their efforts.

Unlike their predecessors, the Wrights realized that control of an aircraft was at least as important as lift and thrust. Their crucial inspiration was understanding that aircraft would fly in three dimensions: climbing and descending (pitch), left and right (yaw), and roll (the banking, tilting motion that in conjunction with the rudder sends a plane into dramatic, sweeping turns). Roll, especially, had been largely ignored or unimagined by their predecessors. Hallion writes that the Wrights, as cyclists, visualized an airplane turning much as a bike rider makes a hard turn—by leaning into it. John Anderson, curator of aerodynamics at the National Air and SpaceMuseum and author of The Airplane—A History of Its Technology, says the Wrights’ “longest-lasting technological contribution is purely and simply flight control. Wilbur Wright was the first person to understand how an airplane turned.”

Simple rudders, like those used to steer boats through water, and elevators (like rudders, except horizontal) were enough to move a plane up and down or left and right. But the third dimension, making a plane bank and turn, required a wholly new approach. The Wrights’ first breakthrough was realizing that air flowing across the wings could be used to push one wing down while it lifted the other—“rolling” the plane through a banked, leaning turn. Their next was figuring out how to get both wings to move the right way at the right time—a beautifully simple concept called wing-warping, which involved twisting the entire wing to facilitate turning.

The Wrights’ combination of creativity and engineering skill continues to amaze scholars today. “They had the ability to visualize machines that hadn’t been built yet,” Crouch says. From the time they hit upon wing-warping as the solution for moving an aircraft in three dimensions in the spring of 1899, it was only four and a half years until their epic, if brief, powered flight at Kitty Hawk. As Hallion puts it, “The Wrights, when they got their act together, moved with incredible speed.”

At first, the airplane’s potential beggared the imaginations of the most progressive scientists. Too expensive for anyone but rich daredevils and too dangerous for regular commercial use, the Wrights’ machine was laughed off as frivolous; even the brothers thought that only national governments would have the resources to build and fly airplanes. “It is doubtful if aeroplanes will ever cross the ocean,” the eminent Harvard astronomer William Pickering scoffed in 1908, according to Hallion’s history. “The public has greatly overestimated the possibilities of the aeroplane, imagining that in another generation they will be able to fly over to London in a day. This is manifestly impossible.”

Such disdain chilled U.S. investment in aviation. Between 1908 and 1913, the U.S. government spent only $435,000 on aviation—less than Germany, France, Chile and even Bulgaria. European inventors and entrepreneurs were soon building better, faster and more stable planes than were the Wrights. “The Wright airplane was superseded by European designs as early as 1910,” says Jakab. German, Russian and especially French aviators and inventors soon dominated the skies, as our vocabulary attests; “aviation,” “aileron,” “fuselage” and “helicopter” all have French origins.

For all the Wrights’ achievements, their aircraft were still iffy. Half-a-dozen pilots were killed flying Wright flyers in a one-year period starting in 1909; other early planes were also dangerous. “Europeans weren’t learning from the Wright experience how to fly, they were learning how to fly better,” Hallion writes. Designers like Louis Blériot moved the Wrights’ “pusher” propellers to the front of the plane, which simplified the design (a rear-mounted propeller requires more elaborate structures for the rudders and elevators). The original biplane configuration—which was strong, light and generated a lot of lift—dominated airplane design until the early 1930s, when monoplanes, which are faster, took over.

At the start of World War I, the airplane had come into its own as a military and commercial technology. The opencockpit, largely wood-and-fabric airplanes jousting in Europe’s skies—planes like the British Sopwith Camel and the German Albatros—were faster and far more nimble than the Wright Flyer, but still dangerous. Heroes like Manfred von Richthofen (the “Red Baron”) and America’s Eddie Rickenbacker created the mystique of the fighter ace, but thousands of others perished in the air. In 1917, the life expectancy of a British fighter pilot in a combat zone, Hallion writes, was three weeks.

But the war speeded up development of the fledgling aviation industry. The first passenger flight had been in 1908, when Wilbur Wright carried one Charles Furnas during tests of the Wright Flyer. Scheduled passenger flights did not begin in earnest until January 1, 1914, when Tony Jannus, an entrepreneurial Florida pilot, started flying $5 hops across TampaBay. Planes flying at low speeds and low altitudes were buffeted by winds, causing a bumpy—and often sickening—ride. Poorly ventilated cabins filled with engine exhaust and gas fumes. And bad weather kept planes on the ground, making air travel unreliable. Yet public demand accelerated.

In the 1920s and ’30s, investment by industry and government fueled innovation. Wood frames and cloth skins gave way to allmetal designs, which in turn made possible larger, stronger craft, streamlining, sealed cabins and high-altitude flight. Also important were reliable flight instruments such as the artificial horizon, altimeter and directional gyroscope, crucial to flying in poor weather (and keeping airlines on schedule). By 1932, U.S. airlines were flying more than 475,000 passengers a year.

In 1935, aviation reached a new peak—and, oddly perhaps, something of a plateau—with the development of the Douglas Aircraft Company’s DC-3. With 21 seats, all-metal construction, a streamlined design, retractable landing gear, automatic pilot and a cruising speed of almost 200 miles per hour, the DC-3 is considered by many experts the pinnacle of the propeller-driven plane, and set the pattern for planes we know today.

As new engine designs drove propellers faster and faster—at their tips, they broke the sound barrier—engineers came up against baffling aerodynamic properties. Shock waves and unpredicted turbulence undermined performance. Propellers lost efficiency and thrust when they neared supersonic speeds.

The man who overcame that limit was not a professional engineer. Frank Whittle, a machinist’s son and Royal Air Force pilot, came up with the idea for a jet engine while serving as a flight instructor in the early 1930s. “Whittle was an odd duck pushing an idea everyone thought was kind of nuts,” says historian Roger Bilstein, author of Flight in America: From the Wrights to the Astronauts. “Nobody thought it would work.”

Whittle persisted, eventually scraping together the resources to design a workable jet engine on his own. The concept, at any rate, is simple: air coming in at the front of the engine is compressed and combined with fuel, then ignited; the burning mixture roars out the back of the jet, generating tremendous thrust while passing through turbines that power the compressors in the front of the engine.

Whittle’s jet engine was first tested in the lab in 1937 and, four years later, powered a specially designed fighter at an air base near Gloucester, England. Pilots watching the top-secret test flight from the side of the damp airfield were baffled. “My God, chaps, I must be going round the bend,” one officer reportedly said later. “It hadn’t got a propeller!”

Meanwhile, a German engineer named Hans von Ohain had been developing his own jet engine. In 1944, a handful of jet fighters and bombers, including the Messerschmitt Me 262—the world’s first operational jet—saw service in the Luftwaffe. In America, military brass put jets on a back burner, convinced the war would be won with conventional airplanes, and lots of them. Diverting resources to work on the unproven jet, authorities insisted, would be a waste of time. But after the Allies swept through Germany at the end of the war, they recruited dozens of German jet and rocket scientists, including Wernher von Braun, and then took them to the United States in “Operation Paper- clip.” The plan laid the groundwork for decades of U.S.-led innovation, from immediately useful jet technology to advances in rocketry that would ultimately make the space program possible.

Jet propulsion technology was the most important thing in aviation since the Wrights. “The jet wasn’t a refinement of anything, it was a complete breakthrough,” says NASM’s Anderson. “A whole second era of aviation was opened up by Whittle and von Ohain.” Yet the jet’s inventors never got the recognition the Wrights enjoyed. Whittle’s patents were appropriated by the British government during the war, and von Ohain quietly began a new career in 1947—as a U.S. Air Force propulsion scientist.

Yet it would take years of painstaking work to turn the jet plane into reliable transportation. In the early days, fighter jet pilots had a one in four chance of dying in an airplane accident. Supersonic speeds, at least about 650 mph, required rethinking conventional notions about aerodynamics, control and efficiency. The design of the X-1, which broke the sound barrier over California’s MurocDryLake in 1947, was based on the .50-caliber bullet, an object that engineers knew went supersonic. It was flown by laconic West Virginian test pilot Chuck Yeager, a veteran World War II ace who counted two Messerschmitt 262s among his kills.

The bravery of those test pilots is what we tend to remember of jet travel’s early days. But perhaps more important was the massive government expenditure on aviation and space research in the 1950s and ’60s. By 1959, the aviation industry was one of the largest employers in America’s manufacturing sector, with more than 80 percent of its sales in the decade and a half after World War II to the military. America’s aviation and space successes became potent symbols in the cold war, and the booming aerospace industry got what amounted to a blank check from the government. After all, as a character in the movie version of The Right Stuff observed, “No bucks, no Buck Rogers.”

“Government investment in things related to flight drove a whole broad front of technological development,” Crouch says. “One thing after another developed because it was somehow related to flight, and governments were spending money on it.” Computers became ubiquitous aviation tools, from aiding design of complex aircraft to forming global ticketing networks. The jet engine also took civil aviation to new heights—and speeds. Boeing introduced a prototype of the 707 passenger jet in 1954 that could fly more than 600 mph (three times faster than the DC- 3). Four years later, Pan American began regular 707 service from New York to Paris, ushering in the jet age.

As the hard-won lessons of military test pilots yielded safer, more stable jet designs, the very shape of the world began to change. From massive B-52 nuclear bombers capable of flying nonstop from Omaha to Moscow in 11 hours, to passenger jets that could cross the Atlantic in 7 hours, the jet made international travel accessible to almost everyone. Big passenger jets became common—the 452-passenger Boeing 747 debuted in 1969— and the number of people who flew climbed steadily each year.

Supersonic passenger planes were the next obvious frontier. But with the exceptions of the Soviet Tupolev TU-144, which first flew in December 1968, and the Concorde, a joint venture between France and Britain that took off two months later, supersonic passenger travel would remain largely a novelty. Both planes were a bust financially. In almost 30 years flying across the Atlantic at twice the speed of sound, the gas-guzzling Concorde never broke even. Air France ceased regularly scheduled Concorde service this past May and British Airways in October. Nonetheless, entrepreneurs and politicians have continued to float futuristic (and so far impractical) ideas, like the Orient Express, a massive supersonic transport that would carry up to 200 passengers from New York to Beijing in two hours, skipping like a stone across the earth’s atmosphere at Mach 5.

Attaining ever-higher speeds hasn’t necessarily been the highest priority for the military. Since the 1970s, military planners have emphasized maneuverability and stealth. But the new planes, with smaller, angled wings and control surfaces, tended to be unstable. That changed with the development in the 1970s of onboard computers, or “fly-by-wire” systems, in aviation lingo, capable of making thousands of adjustments per second to rudders and other control surfaces. The Northrop B-2 stealth bomber and the Lockheed F-117ANighthawk stealth fighter, bizarre matte-black bundles of strange angles and stubby wings designed to disappear from enemy radar, seem to defy the laws of aerodynamics with the help of sophisticated software. The ultimate fly-by-wire technology, unmanned aerial vehicles, or UAVs, are remote-controlled drones, which have already seen service in the skies over Afghanistan and Iraq.

To many aviation experts, airplane technology seems to have hit another lull in the rate of progress. “That’s the big question: Is the airplane in its form now a mature technology?” says NASM curator Jeremy Kinney. “The airlines are doing very well with wide-body, turbofan planes carrying hundreds of people, and the military is essentially innovating refinements. Is there even a next plateau?”

Engineers hope so. “Sure, we’ve reached a certain level of maturity over the last part of the 20th century that some see as a plateau, the same as in the ’30s,” says the Smithsonian’s Anderson, a former chairman of the University of Maryland’s Aerospace Engineering Department. “I believe this is a platform from which we’ll jump off and see dramatic advances.” In addition to improvements in the efficiency and performance of existing aircraft, technological refinements may soon allow amazing accomplishments: fly-by-wire systems that keep a plane aloft with one wing shot off, the reduction or even elimination of sonic booms, and unmanned aircraft capable of dramatic maneuvers that would kill a pilot.

Curiously, some of the most advanced research going on right now bears a striking resemblance to innovations the Wrights made more than a century ago. At NASA’s Dryden Flight Research Center in Edwards, California, engineers in the Active Aeroelastic Wing Program have equipped an F/A- 18 Hornet fighter plane with more flexible wings that test the possibilities of aeroelastic wing design—essentially a version of the Wrights’ wing-warping, albeit one that uses very advanced computer systems to induce wings to change shape at supersonic speeds. Aeroelastic wings make rolling, banking turns possible by twisting the wing itself, improving performance at supersonic speeds. “Very few birds fly with ailerons or leading edge flaps,” quips Dick Ewers, a NASA test pilot on the project. Instead, he says, birds change the shape of their wings, depending on how fast or slow they’re going and whether they’re turning, climbing, diving or soaring. “Airplanes spend a lot of weight and money making wings stiff,” he goes on.The aeroelastic wing will eventually do away with flaps and move the plane by changing the shape of the wing itself, he predicts: “Rather than stiffen the wing, we want to let it be flexible and take advantage of it.”

A Centennial of Flight logo on the prototype plane proudly heralds the project’s remarkable connection with tradition. Planes of the future may share an inspiration with the Wrights, who successfully guided their Flyer in three dimensions by shifting the shape of its wings. “One hundred years later, we may discover that the Wright brothers’ answers were more correct aerodynamically than what we’ve been living with for 80 years,” says Dave Voracek, the project’s chief engineer. “We’ve really come full circle.”