by Justin Schell
One of the more remarkable facts of the Wright Brothers’ story is that it took them only four years to solve the problem of controlled, sustained “heavier than air” flight. From 1899, when they were running a bicycle construction and repair shop in Dayton, OH and wrote the Smithsonian for whatever materials they would send them on the investigations of flight, to their own successful flights in Kitty Hawk in 1903, there were many incredible experiments and discoveries along the way.
One of these that interested me the most was their fundamentally different way of approaching the design and testing of aircraft. For many investigating flight, it was a series of trials and errors, a cycle of building a machine, crashing, building a slightly different machine, crashing again, and repeating, sometimes with catastrophic results. Otto Lillienthal, a German flight pioneer and one of the most important influences on the Wright Brothers, died when his aircraft crashed in 1896.
The Wright Brothers were determined to do things differently. They emphasized small-scale testing and, in the process, essentially invented the field of aeronautical engineering. One of the most fascinating example of this was their creation of a wind tunnel in 1901 to test various wing shapes (or aerofoils) that they would use for their machines. All of these aerofoils were crafted by the Wrights, each one fitting into the palm of their hand. They had first attempted this kind of work by placing the aerofoils on an inverted bicycle wheel exposed to outside winds, but found that creating their own wind (via a fan and engine of their own design) could produce more reliable results. While they were not the first to build a wind tunnel (there are examples dating back to the 18th century), they were the first to use it to test the components of their flyers in a more rigorous way.
The problem the Wrights were trying to solve was that of lift and drag, specifically which wing shape would have the best ratio between the two. To do this, they crafted a set of balances that could sit inside of the wind tunnel. The aerofoil would then be attached to the balance and wind from the fan would be sent through the tunnel and moved through different “angles of attack,” or the angle at which wind hit the aerofoil. They tested between one and two hundred surfaces, with detailed results recorded for 57 of them. Some were made of steel, others of galvanized iron, some were straight-edged, others with a variety of curved surfaces, and some modeled after bird wings. (These results are collected in McFarland’s two-volume collection of the Wright Brothers’ correspondence.)
This process answered a key questions for the Wrights: which aerofoil had the best shape for their fliers? The answer was aerofoil #12.
While some wings generated more lift than others, they had a more severe stall point, which meant the machine could lose altitude much more quickly, resulting in a loss of control and a possible crash. While one with the requisite mathematical skills might be able to see this in the data itself, it can be more easily seen in the graphs the brothers made of their aerofoil tests.
While aerofoils 15, 16, and 17 produced more lift, one can see the much sharper drop once the maximum lift is reached. Compare this to #12: although it did not reach the same degree of lift as 15, 16, or 17, it had a much more stable descent. This aerofoil not only was chosen by the Wright Brothers for their machines, it has been used ever since by the majority of airplane construction.
Much of the aeronautical engineering materials from the Wrights, including the aerofoils, notebooks, and graphs, were donated to the Franklin Institute in Philadelphia by Orville later in his life. Some are in display in “The Franklin Air Show,” their permanent exhibit that details not only the history of flight but also interactively demonstrates the basic principles of flight. I visited the Franklin earlier this year and met with John Alviti, the Senior Curator for the Franklin, to talk about “Test Pilot” and specifically the Wrights’ wind tunnel experiments. After discussing some of the details of the experiments, he asked, “Would you like to see the wings?” Of course, I eagerly agreed. Donning white gloves, I held in my hand the very same aerofoils that the Wrights held in theirs more than a century ago, these small components that played such a large role in solving the problem of heavier-than-air flight.
Learning more about the Wrights’ experimentations with wind tunnels and aerofoils not only has taught me much about their own process of invention, but also how exacting airplane design is, how much engineering goes into making the planes people fly (and fly in) every day able to get off the ground, stay in the air, and withstand such a wide variety of winds through such a wide variety of conditions. Yet even more it made me appreciate the accomplishments of these two men who never graduated high school and solved the problem of flight that had stymied many for centuries in four short years.