Tom Crouch is Senior Curator of the Division of Aeronautics at the National Air and Space Museum in Washington, D.C., and has just published two books on the Wrights: The Wright Brothers and the Invention of the Aerial Age (National Geographic, 2003, with Peter L. Jakab), and a new edition of The Bishop's Boys: A Life of Wilbur and Orville Wright (Norton, 2003).
Getting under way
NOVA: Two brothers running a bicycle shop seem an unlikely pair to take on the challenge of building a flying machine. How did they get into it?
Tom Crouch: At the end of the 19th century, Wilbur Wright was a young man looking for a challenge against which he could measure himself. He was taking it easy in life. He was approaching 30, living under his father's roof. He hadn't married, didn't have children. The only thing that he'd done in life was to run two very small businesses with the help of his younger brother Orville. I think he had the sense that, if he was ever going to make his mark in the world, this was the time to do it. So he was looking for the challenge that would do that for him, and one of the great technical challenges at the end of the 19th century—and he was a technical man—was the airplane.
How did he begin tackling this challenge?
The first thing he did was to read everything he could lay his hands on, everything in sight. His father had some simple books on flight in nature in his library, and the Dayton Public Library had a handful of things on flight. When he had exhausted the local resources, Wilbur wrote to the Smithsonian Institution asking for more information on flight. Richard Rathbun, the assistant secretary of the Institution, sent him a handful of pamphlets and a list of additional books that he could purchase, which he did. So he began with an assessment of the problem, finding out what other people had done and making decisions about where he should focus his effort.
What did he learn from this early research?
Well, if you think about an airplane, it really requires at least three separate systems to function. You have to have wings that will lift you into the air. You have to have a propulsion system that will move the wings through the air to generate lift. And you have to have a control system, a means of balancing the airplane when it's in the air.
As he read the material he'd collected, Wilbur discovered that people had made wings that would lift. Otto Lilienthal had built gliders that carried him on over 2,000 flights through the air. Samuel Langley had built wings that carried his rather heavy models through the air. Wilbur assumed he could rely on those folks for his initial information on wings. He didn't think propulsion would represent any Earth-shattering problem either. People in Dayton were building relatively lightweight internal combustion engines to power automobiles and motorcycles and whatnot, and he was confident that when the time came the propulsion would be there. Control was the one issue that had received less attention than wing design or propulsion, so that's where he decided to focus his effort.
How did he and Orville approach the problem?
The Wrights thought of flight as something that happened in three dimensions. A lot of other experimenters had thought about it as a two-dimensional sort of thing, as though an airplane were going to be a cart running on a road or a ship running on the sea. Basically, all the other individuals who were interested in the airplane at the turn of the century had thought about the notion of an inherently stable flying machine—a flying machine that would, if it were struck by a gust, return itself to a stable position automatically.
The Wright brothers went in a completely different direction. From the beginning, their goal was to devise a control system that would give them absolute command over the motion of a machine in every axis all the time. They were much less concerned about stability than they were about control.
That's not so surprising—they were cyclists, after all. Other experimenters were saying that if you tried to develop a control system that put the airplane at the command of the pilot all the time, it would drive him crazy. No human being could keep up with the motion of something that was essentially balanced on the head of a pin.
"Wing warping was one of the first great conceptual breakthroughs that the Wright brothers had."
But as cyclists the Wright brothers said to themselves, if you tried to get someone who'd never seen a bicycle to understand the act of riding—"What, you're going to roll down the street on this thing with two narrow rubber tires, and you're going to be balancing while you're operating the handlebars?"—it would sound like the sort of feat that only the world's greatest acrobat could accomplish. Yet they knew, of course, that once you learn how to ride a bike, you internalize that, and it becomes perfectly natural and instinctive; you don't even think about it. They were sure the same thing would be true of a flying machine.
So how did they devise their control system?
If you think about an airplane moving through the air, it has to be controlled in three separate axes. To the Wrights, the notion of how to control the airplane in two of those axes wasn't so difficult. Ships had had rudders for millennia, and a rudder could be used to control the airplane in the yaw axis—nose right, nose left. The idea of an elevator, a rudder that sat horizontally on its side so that it could be used to control the airplane in pitch—nose up, nose down—didn't require any great feat of the imagination. The difficulty was how you would control the airplane in the axis that was virtually unique to the flying machine: the lateral, or roll, axis. It was very difficult to imagine a control system that would give you command over that motion.
How did they crack that problem?
As Wilbur told the story, he was in the bicycle shop one day when a customer came in and purchased an inner tube. Wilbur was just idly fiddling with the inner-tube box in his hands when he realized that if you could create motion on the wings of a biplane so that the wing tip on one side was forced up while the other side was forced down, then you would have a means of controlling the airplane in lateral motion, in the roll motion. This technique—putting a twist of this sort all the way across the wings of a biplane to control its motion in roll—became known as wing warping. It was one of the first great conceptual breakthroughs that the Wright brothers had.
When did they try it out?
They put this roll-control idea into practice with a kite they constructed in the summer of 1899 and tested in Dayton, and it seemed to work reasonably well. So they began to plan for their first full-scale machine, the 1900 glider, which would embody roll control and give it a test in a full-scale machine designed to carry a human being.
From the outset, they recognized that they had two problems. They not only had to figure out how to build the flying machine, they had to fly it as well. They had to train themselves as pilots as they went along. Wilbur once suggested that there were two ways of learning to ride a fractious horse. You could sit on the fence and watch somebody else try to do it, or you could try to do it yourself. And the latter method is much more effective.
Of course, there were risks in that. Lilienthal and others had been killed trying to fly.
The notion of safety was always uppermost in their minds. They were careful, methodical fellows. They knew that this was going to be relatively risky, whatever they did. They wanted to reduce that risk to the minimum. Wilbur wrote to his father on his first trip, for example, that he recognized there were dangers, but he and his brother were going to be very careful, move very slowly, be very cautious. And they always were, from the beginning to the end. They moved step by step, methodically, and didn't take any risks that they didn't have to take.
How did they go about moving from a kite to a glider that could carry their weight?
They began with an insistence that they calculate the performance of their machine before they built it. They were engineers, after all. To do that, there were certain factors that they knew. They knew what the wind speed was going to be. They knew what the weight of their machine was going to be. And they knew what the area of the wing of their machine was going to be.
But there are two coefficients, small numbers, that you have to plug into the equation to describe the fluid in which you're operating—air—and to describe the changing forces as the airfoil changes angle of attack. It was those two little coefficients that ultimately gave them problems.
Of what sort?
When the Wrights designed their first glider in 1900, they began with data that they had inherited from Otto Lilienthal. They assumed that since Lilienthal had flown rather well in his hang gliders, the data on which he had based those gliders must be correct. So they adopted a simple table of lift with changing angle of attack that he had put together. That was the basis for the design of their first two gliders in 1900 and 1901.
But in experimenting with those gliders the Wright brothers discovered that those machines were producing roughly 20 percent less lift than their calculations had predicted. Now, these guys were engineers. They wanted to be certain of what was going on, and they wanted performance to match calculation. They knew there was a problem there somewhere. The difficulty was how do you isolate the problem?
They began by building a mechanical representation of the simple algebraic equations they had used to calculate the performance of their gliders. These guys were bicycle builders, after all. What they did was take a bicycle wheel and mount it horizontally and free to spin in front of the handlebars of one of their bicycles. At a particular point on the wheel's rim, they affixed a flate plate, and at another point on the rim they attached a curved plate approximating a cambered airfoil. Both metal plates were of the same size and mounted vertically. The size and position of these two surfaces represented the equation they were using to calculate performance.
What the calculations told them was that, if they rode their bicycle with this device mounted in front of the handlebars through the streets of Dayton, with the tiny "wing" angled at five degrees to the wind coming at it, the wheel should remain still, because the pressure on the flat plate should equal the force on the curved "wing." That is, if the equation they were using and the information they were plugging into it was accurate, this thing should be fairly steady as they rode it through the streets.
And was it?
It wasn't, as it turned out. In fact, the Wrights discovered that they had to set the cambered wing at three times the angle that their calculations said in order to balance the wheel. And that was simply confirmation of what they had discovered with the gliders. There was a problem with the information they were using to calculate performance—information that they had inherited from their predecessors.
So how did they arrive at the right information?
To discover where the precise errors lay and to gather their own data that would be absolutely accurate, they had to take another approach. They could have built a great number of gliders with separate wing shapes and airfoils and that kind of thing, but rather than doing that they took a much smarter approach. They built a wind tunnel that they ran in the bicycle shop in Dayton in the fall and early winter of 1901.
"At that point, they stood head and shoulders above every other experimenter in the world."
A wind tunnel is a really simple device. Rather than moving a wing forward through the air, you position it in one spot and run air over the top of it. It makes no difference to your data whether the wing is moving forward through the air or whether the air is moving over the wing. And in a wind tunnel you're not using full-scale wings but small model wings. The Wright brothers created as many as 200 of these little model wings, and they seriously tested upwards of 50 of them and gathered all sorts of accurate data with which they could then do accurate calculations of performance. At that point, they stood head and shoulders above every other experimenter in the world.
What did their wind tunnel look like?
It's just a wooden box about six feet long. On the far end there's a fan that moves air through the length of the tunnel. (The fan that drove air through the tunnel was powered from a line shaft in the roof of the bicycle shop.) On the working end of the wind tunnel you have an instrument that gathers data on the specific airfoils that are being tested. It's called a balance, and it's made out of hacksaw blades, bicycle spoke wire—simple material they had around the bicycle shop.
When you break it down the balance easily fits into a shoebox, and yet it's every bit as important to the story of the Wright brothers as the gliders they built and flew at Kitty Hawk. It was with this instrument that the Wrights were able to gather bits of aerodynamic data so accurate that modern engineers, working with multimillion-dollar wind tunnel facilities, are only able to improve on it by a percentage point or two.
The propeller was another significant advance of theirs, right?
The propeller was one of the great technical problems that the Wrights faced and solved, and when you look at the way in which they did it, it really does underscore the nature of their genius. When they originally thought about the problem of propeller design, I think they assumed that it wasn't going to be so difficult. People had been studying things that rotate—windmill blades and propellers on ships—so the Wrights assumed that there was some sort of a theoretical base there that enabled you to calculate propeller performance. When they got serious about their propulsion problem after their wonderful 1902 season, they discovered that that theoretical base simply wasn't there, and they were going to have to do that themselves.
The great breakthrough occurred when they stopped to think about the problem and said that essentially a propeller isn't an air screw at all; it's not like a screw going into wood. It's much more like a wing; it's developing lift. Rather than moving forward through the air, it's rotating, and the lift becomes the thrust that moves the airplane forward.
Once they'd made that breakthrough it occurred to them that, since they were going to know the revolutions per minute at which the propeller would be turning, they could calculate the speed at which the propeller would be turning at any point along the blade. That meant that they could go back to their wind tunnel data, and they could pick out an appropriate airfoil for the appropriate conditions at every point along the blade. Having done that, they made templates, carved the propeller, and it worked. They had a propeller the performance of which they could calculate.
Engineering the age of flight
The Wright brothers were discovering aspects of flight that no one had known before. Would you consider them engineers or scientists?
A scientist is primarily interested in uncovering some new truth about the universe, some new fact about the way in which the universe runs. Engineers build things. They build machines, they build bridges, they build buildings, they build systems. Their task is to design and build something that's going to work. That means that they're sometimes less concerned with uncovering absolute truth. They're gathering data that's going to help them to build more efficiently this thing that they're building, whether it's an automobile, a bridge, or whatever.
If you look at the way in which the Wright brothers gathered data, they really weren't trying to understand precisely why a wing lifts or an airplane flies. What they were doing was gathering points of data about the forces operating on a wing at particular angles of attack, information that they could plug directly into their calculations for the design of an airplane. It was a very specific step that they needed to make the thing work more efficiently.
The Wright brothers weren't tinkerers. They were engineers in the sense that they calculated the performance of this thing that they were building and then tested the machine against that calculation. That's what engineers do—they isolate problems, gather data to solve the problems, test and make alterations on the basis of their results. So while there are blind alleys and disappointments, it's still very much a story of moving forward. Even from mistakes you discover something that's useful in moving you forward.
"There aren't many days when history really changes, but December 17, 1903, was one of those days."
If you consider some European flying machine experimenters in the early 20th century—Louis Blériot, for example—they were developing widely divergent configurations of aircraft. That's not true with the Wright brothers. They started with a basic design that they had good reasons for selecting, and they kept improving on it, making discoveries that enabled them to change it, improve it. That's the way they stepped toward the invention of the airplane.
What does December 17, 1903, represent for you?
There aren't many days when history really changes, but December 17, 1903, was one of those days, because it was the day on which an airplane flew for the very first time, and the airplane's an invention that has shaped the history of the 20th century, from the way in which we do commerce to the way in which we fight our wars. It has absolutely shaped our time. It was an important day, of course, for Wilbur and Orville Wright. They knew that this would be the culmination of everything they'd worked for.
Can you sum up what transpired that day at Kitty Hawk?
Well, they started out at 10:35 that morning with the first flight, which Orville made. It was quite short—120 feet, 12 seconds. After that Wilbur made the second flight, Orville the third. Wilbur's fourth flight, 852 feet in 59 seconds, really was something to celebrate.
But it was cold, so once they had the airplane back, everybody but one guy who was detailed to hold the airplane down went into the shed to warm their hands. While they were in there, a gust came up and tumbled the airplane and transformed this machine into torn fabric and broken wire and smashed wood. So the total career, the total air time of the world's first airplane was four flights of less than two minutes total. But it was enough to introduce an invention that would reshape the history of the world.
When I think about some of the difficult times they would have in the years after 1903, I like to remember Orville's comment that the period from 1899 to 1903, when they were working just the two of them together on technical problems, on the invention of the airplane, was the happiest time of their life. And December 17 was the culmination.
How much did this whole effort cost them?
Much less than it did other people. If you look at Samuel Langley, for example, who was the third Secretary of the Smithsonian and was experimenting during this same period, he was spending taxpayers' money in large chunks, where the Wright brothers were working much more effectively and much less expensively. From the beginning to the end, from 1899 to the end of the 1903 flying season, they probably spent less than $1,000, while Langley spent about $50,000 during that period. They flew; he didn't.
Inventors of other important machines have not necessarily captured the public's imagination to such an extent as the Wright brothers. How do you explain their enduring appeal?
I think one of the reasons that the Wright brothers have such extraordinary appeal—not just for Americans but for people all over the world—is the fact that you have these two bicycle makers from Dayton, Ohio, who were also engineering geniuses. They became world figures essentially because of their genius and because of character traits—their strength of character, their determination, their perseverance, their striving to overcome obstacles and doing it and pursuing this thing to the end. Those are things that we admire in all people, and these guys were models of that sort of determination and perseverance.