Tunnel Vision: How Wind Tunnels Have Propelled Flight

Modern Wind tunnels are so advanced that they exceed speeds beyond the technological limit of manned flight. Wind tunnel testing labs exist throughout the world and the United States, serving as an important piece of the aerospace industry’s infrastructure. From the humble beginnings of whirling arms, the primitive, yet innovative, design of the Wright brothers’ wind tunnel, to the full scale testing model produced by the National Advisory Committee for Aeronautics (NACA) in 1938, wind tunnels have shaped aerodynamic design and the study of aeronautics for centuries.

Whirling Arm Paves the Way

Before the invention of the wind tunnel, early aeronautic experimenters used whirling arms. Created by Benjamin Robins in the mid-1700s, the first prototype “had an arm 4 feet long. Spun by falling weight acting on a pulley and spindle arrangement, the arm tip reached velocities of only a few feet per second.”¹ Advanced enough to produce most of the systematic aerodynamic data gathered until the end of the 1800s, the mechanics of the whirling arm revealed the need for a more stable and controllable contraption to test velocity and other forces of flight, such as lift and drag. However, the design of the whirling arm produced too much turbulence and made it difficult to mount instruments for testing when it spun at high speeds.

Despite its problems, the whirling arm paved the way for the more sophisticated and technologically advanced wind tunnel. Wind tunnels are large structures that simulate flight by flowing air around objects, providing data on aerodynamics. Types of wind tunnels vary based on desired airflow conditions and include subsonic, transonic, and supersonic speeds. Though most wind tunnels use miniature models, some wind tunnels can accommodate full-size vehicles.

The World’s First Wind Tunnel

In 1871, Great Britain’s Francis Herbert Wenham created the world’s first wind tunnel. One of the most influential experimenters in the pre-Wright era, Wenham was serving on a research committee under the direction of the Aeronautical Society of Great Britain when he designed and built the first wind tunnel. Wenham’s design included a series of mounted ‘planes’ on a horizontal arm, set at various inclinations. These mounted planes vibrated when blasted with air, allowing Wenham and his committee to assess the direct force of the wind on each plane and record early lift and drag data. Soon other early inventors also began to design their own experiments. Otto Lilienthal, Sir Hiram Maxim, and Samuel P. Langley were just some of the great minds who created whirling arms and/or wind tunnels to test cambered airfoils, engines, and propellers, all with varying degrees of success in pursuit of powered, heavier-than-air flight.

The tests conducted by Wenham, Lilienthal, Maxim, Langley, and others created the accepted lift and drag equations of the time. After the Wright brothers had solved the question of control through their technique of wing warping applied to their 1899 Wright Kite, they shifted their focus to lift and drag. During their experimentation with their 1900 and 1901 Wright Gliders, the brothers hypothesized that the lift and drag equations were incorrect; none of the gliders they built between 1900 and 1901 generated the expected amount of lift that the data estimated. Drawing on the expertise they gained while working with bicycles, the Wrights proposed that aircraft, like bicycles, were inherently unstable objects that could still be controlled despite their unstable nature. If the Wrights could find a way to stabilize unstable aircraft, they would become one step closer to achieving flight.

Wright Brothers Revolutionize Wind Tunnel Technology

The first 1900 Wright Glider failed to generate the expected amount of lift according to the mathematical calculations the Wrights completed. After revising the Glider a few times, the Wrights began to question the math. Could it be possible that the lift and drag equations were wrong? Unphased by their failures, the Wrights conceived a bicycle with an additional wheel mounted atop horizontally. Attached to the additional wheel was a model wing and flat plate. As they rode the bicycle, the wind balanced the objects, revealing inconsistencies in their predecessors’ data. Encouraged by their initial findings, they chose to continue their testing by building a wind tunnel.

The Wrights’ use of their wind tunnel and its data was revolutionary for the time, establishing the groundwork for the study of aeronautical engineering. The Wrights tested over 200 airfoil shapes one by one, mounting each inside the wind tunnel and analyzing how air flowed over the shape. They meticulously recorded each test, noting the amount of lift and drag produced by each airfoil. Through this work, Orville and Wilbur determined which airfoil shape would generate enough lift to carry their glider through the air and disproved Smeaton’s coefficient, the value used in lift equations at the turn of the 20th century. This critical data resulted in the success of the Wrights’ 1902 Glider and eventually the 1903 Flyer that made history on December 17, 1903.

NACA Constructs the First Full Scale Wind Tunnel

Aviation and full scale wind tunnels advanced quickly after the Wrights’ first flight in 1903; by 1908 the United States government had awarded a contract to Orville and Wilbur Wright to continue developing aircraft. Air superiority was unheard of at the start of World War I, but became a necessity by the end of the war. Nations around the world understood the power and promise of aircraft and began devoting resources to continue developing cutting-edge technologies. In the United States, the National Advisory Committee for Aeronautics (NACA) authorized the construction of a wind tunnel in 1929. It took two years to build and contained a test section that measured sixty feet in width by thirty feet in height, large enough to mount an entire airplane inside.² Named the Full Scale Wind Tunnel, or FST for short, it was the largest wind tunnel in the world at the time that it was completed.

NACA understood the importance of testing a full-size airplane inside a wind tunnel–“there are full scale effects in applying aerodynamic data obtained on small models that compromise the data when applied to the ‘real thing.’ This [was] especially true with data for aerodynamic drag, an important datapoint to measure.”³

Only a few years after its creation, the benefits of testing aircraft in the FST instead of a smaller scale model became evident when the US Navy struggled to understand why the XF2A Buffalo failed to reach the expected top speed. The Navy Bureau of Aeronautics arranged to test the Buffalo in the FST, where NACA staff identified the components of the aircraft which produced excessive drag. The aircraft manufacturer used this information to redesign the aircraft, increasing the top speed and proving the utility and necessity of the FST.⁴

The Department of Mechanical and Aerospace Engineering (MAE) at North Carolina State University has developed multiple wind tunnels in the Turbulent Shear Flow Laboratory, including the hypersonic wind tunnel pictured above. The hypersonic wind tunnel can reach speeds up to Mach 6, or four times the speed of sound. Photos courtesy of NC State University

NC State University’s Hypersonic Wind Tunnel

Since the introduction of the FST, wind tunnel technology has continued to evolve alongside the aeronautical industry. Many wind tunnels and testing labs exist all over the United States, testing aircraft, jet engines, motorcycles, and even NASCAR racecars.⁵ As the birthplace of aviation, it is fitting yet serendipitous that North Carolina is also home to a wind tunnel lab at the precipice of hypersonic technologies. The Turbulent Shear Flow Laboratory at North Carolina State University houses multiple wind tunnels that operate at many speeds, from the low speed such as a car driving on a highway, up to hypersonic speeds which exceed 4,000 mph⁶. Dr. Venkat Narayanaswamy, a professor for the Department of Mechanical and Aerospace Engineering (MAE), says, “this facility is one of a kind in the entire nation…what we are doing is mainly looking at technological bottlenecks. Understanding the source of that bottleneck, how we can offset the bottleneck and develop new innovative approaches to enable that.” Narayanaswamy believes these “technologies [will] enable the future leadership of our country and [help] with what we call a space economy, meaning how we access the infinity of space for human benefits and to elevate our standard of living”⁷. History shows that wind tunnels have propelled aviation since before the advent of the aircraft and they will continue to propel us into the future that awaits us in space.

To learn more about NC State’s Turbulent Shear Flow Laboratory, visit their website: https://tsfl.wordpress.ncsu.edu/.

1. “Whirling Arms and the First Wind Tunnels,” National Aeronautics and Space Administration, last modified May 13, 2021, https://www.grc.nasa.gov/www/k-12/WindTunnel/history.html. ↩︎
2. John Anderson, “Sleeker and Faster: The Impact of the Full Scale Wind Tunnel,”  National Air and Space Museum, April 20, 2020, https://airandspace.si.edu/stories/editorial/sleeker-and-faster-impact-full-scale-wind-tunnel. ↩︎
3. Anderson, “Sleeker and Faster”. ↩︎
4. Ibid. ↩︎
5.  Carsten Frederiksen, “The List of Wind Tunnel Testing Facilities,” DEWESoft, February 9, 2023, https://dewesoft.com/blog/list-of-wind-tunnel-testing-facilities.” ↩︎
6. “Mach 6 is Here: Student-built Hypersonic Wind Tunnel is Up and Running,” College of Engineering News, North Carolina State University, July 26, 2024, https://engr.ncsu.edu/news/2024/07/26/mach-6-is-here/. ↩︎
7. “Mach 6 is Here”. ↩︎