On Sunday, August 9, 1896, the sky over Germany’s Rhinow Hills stretched clean as a sheet, the moon chewed the sun in a partial solar eclipse, and a white shape soared between the peaks. It had the spoked wings of a bat and a crescent tail. A bearded man hung beneath: Otto Lilienthal, piloting a new glider, maneuvering by shifting his weight, aiming to create a powered flying machine. A gust of wind caught the glider and tilted it up. He swung his body but was unable to right it. His great white bat fell fifty feet, and Lilienthal thrashed in its jaws. His back was broken, and he died the next day. His last words were “Sacrifices must be made.”
Orville and Wilbur Wright read the news at their Wright Cycle Company store in Dayton, Ohio. Lilienthal’s sacrifice seemed senseless to them.
No one should drive a vehicle he cannot steer, especially not in the sky.
Cycling was a new fashion in the 1890s. Bicycles are miracles of equilibrium. They are not easy to build or ride. When we cycle, we make constant adjustments to stay balanced. When we turn, we abandon this balance by steering and leaning, then recover it once our turn is complete. The problem of the bicycle is not motion; it is balance. Lilienthal’s death showed the Wrights that the same was true of aircraft. In their book The Early History of the Airplane, the brothers wrote:
The balancing of a flyer may seem, at first thought, to be a very simple matter, yet almost every experimenter had found in this one point which he could not satisfactorily master. Some experimenters placed the center of gravity far below the wings. Like the pendulum, it tended to seek the lowest point; but also, like the pendulum, it tended to oscillate in a manner destructive of all stability. A more satisfactory system was that of arranging the wings in the shape of a broad V, but in practice it had two serious defects: first, it tended to keep the machine oscillating; and second, its usefulness was restricted to calm air. Notwithstanding the known limitations of this principle, it had been embodied in almost every prominent flying machine that had been built. We reached the conclusion that a flyer founded upon it might be of interest from a scientific point of view, but could be of no value in a practical way.
In the same book, Wilbur added: “When this one feature has been worked out the age of flying machines will have arrived, for all other difficulties are of minor importance.”
This observation set the Wright brothers on the path to the world’s first flight. They saw an airplane as “a bicycle with wings.”
The problem of the aircraft is not flying: like the bicycle, it is balance.
Otto Lilienthal died because he succeeded at the first and failed at the second.
The Wrights solved the problem by studying birds. A bird is buffeted by wind when it glides. It balances by raising one wingtip and lowering the other. The wind turns the wings like sails on a windmill until the bird regains equilibrium. Wilbur again:
To mention all the things the bird must constantly keep in mind in order to fly securely through the air would take a very considerable treatise. If I take a piece of paper, and after placing it parallel with the ground, quickly let it fall, it will not settle steadily down as a staid, sensible piece of paper ought to do, but it insists on contravening every recognized rule of decorum, turning over and darting hither and thither in the most erratic manner, much after the style of an untrained horse. Yet this is the style of steed that men must learn to manage before flying can become an everyday sport. The bird has learned this art of equilibrium, and learned it so thoroughly that its skill is not apparent to our sight. We only learn to appreciate it when we try to imitate it.
That is, when we try to fly a horse.
These were the Wrights’ first mental steps. Problem: Balance a bucking aircraft. Solution: Imitate gliding birds.
The next problem was how to reproduce a bird’s balance mechanically. Their first solution required metal rods and gears. This caused the next problem: it was too heavy to fly. Wilbur discovered the solution in the Wrights’ bicycle shop while playing with a long, thin card- board box that had once contained an inner tube – something roughly the same size and shape as a box of tin foil or Saran Wrap. When Wilbur twisted the box, one corner dipped slightly and the other rose by the same amount. It was a motion similar to a gliding bird’s wingtips, but it used so little force that it could be achieved with cables. The distinctive double wings on the brothers’ airplanes were based on this box; they called the twisting that made the tips go up and down “wing warping.”
As young boys, the Wrights had loved to make and fly kites – “a sport to which we had devoted so much attention that we were regarded as experts.” Despite their fascination, they stopped during their teenage years because it was “unbecoming to boys of our ages.” And yet, twenty years later, Wilbur found himself cycling through Dayton as fast as he could with a five-foot kite across his handlebars. He had built it with wings that warped to prove the idea worked. He was hurrying to show it to Orville. The brothers had completed their second step.
And so it continued.
The Wright brothers’ great inventive leap was not a great mental leap. Despite its extraordinary outcome, their story is a litany of little steps.
For example, they spent two years trying to make Wilbur’s kite big enough to carry a pilot before discovering that the aerodynamic data they were using was worthless.
“Having set out with absolute faith in the existing scientific data,” they wrote, “we were driven to doubt one thing after another, till finally, after two years of experiment, we cast it all aside, and decided to rely entirely upon our own investigations.”
The Wrights had started flying as a hobby and with little interest in “the scientific side of it.” But they were ingenious and easily intrigued. By the time they realized that all the published data was wrong – “little better than guesswork” – they had also discovered what knowledge was needed to design wings that would fly. In 1901, they built a bicycle-mounted test platform to simulate airplanes in flight, then a belt-driven wind tunnel they used to create their own data. Many of the results surprised them – their findings, they wrote, were “so anomalous that we were almost ready to doubt our own measurements.”
But they eventually concluded that everybody else’s measurements were wrong. One of the biggest sources of error was the Smeaton coefficient, a number developed by eighteenth-century engineer John Smeaton to determine the relationship between wing size and lift. Smeaton’s number was 0.005. The Wrights calculated that the correct figure was actually 0.0033. Wings needed to be much bigger than anybody had realized if an airplane was ever going to fly.
The Wrights used the same data to design propellers. Propellers had been built for boats but never for aircraft. Just as the brothers thought of an airplane as a bicycle that flew, they thought of a propeller as a wing that rotated. The lessons from their wind tunnel enabled them to design a near-perfect propeller on their first attempt. Modern propellers are only marginally better.
The Wrights’ aircraft are the best evidence that they took steps, not leaps. Their glider of 1900 looked like their kite of 1899. Their glider of 1901 looked like their glider of 1900 but with a few new elements. Their glider of 1902 was their glider of 1901, bigger and with a rudder. Their 1903 Flyer – the aircraft that flew from Kitty Hawk’s sands – was their 1902 glider made bigger again with propellers and an engine added. Orville and Wilbur Wright did not leap into the sky. They walked there one step at a time.
An extract from “How to Fly a Horse.”