MOFFETT FIELD, Calif. -- By nearly 40 years, the Arnold Engineering Development Complex 40- by 80-foot wind tunnel predates the establishment of the National Full-Scale Aerodynamics Complex, which it and the AEDC 80- by 120-foot wind tunnel collectively form at the NASA Ames Research Center in California.
The 40x80 predates AEDC itself, which has overseen operations at NFAC for nearly the past 20 years.
It predates the formation of NASA and the creation of the U.S. Air Force.
In June 1944, the giant blades of the 40x80 wind tunnel whirled for the first time. In the 80 years since, the tunnel has been used to test various wings, rotors, propellers, engines, inlets and recovery devices, such as parachutes used as part of the Apollo space program. Due to its size, the tunnel has also been used to conduct aerodynamic testing on both full- and large-scale aircraft models. Aircraft tested in the 40x80 include the A-26 Invader, F-84 Thunderjet, F-86 Sabre, Kaman K-16B, V-22 Osprey, Sikorsky Rotor S-76, AV-8B Harrier II and F-14 Tomcat. A scale model of the space shuttle was tested in the tunnel.
The significance of the 40x80 reaching its 80th year in operation is not lost on those at NFAC.
“We have a great team at NFAC, and everyone here recognizes that our facility is one-of-a-kind and so are the tests we can conduct here,” said NFAC Deputy Director Joe Sacco. “The 80th anniversary of the 40x80 wind tunnel is a real tribute to the brilliant men and women who recognized the need and then designed and built this amazing tool to maintain U.S. leadership in aeronautics.
“I wonder if they realized it would still be as valuable 80 years after they built it.”
Today, the 40x80 wind tunnel at NFAC supports proof of concept, technology maturation and system integration testing, as well as computational engineering code validation.
“Test articles can be powered in the 40x80 wind tunnel so tests can be used to demonstrate new vehicle concepts and validate computational design tools when complex phenomena cannot be modeled accurately without test data to anchor their solutions,” Sacco said. “A 40x80 wind tunnel test will provide definitive performance data on helicopter rotor system designs or turbine powered vehicles with boundary layer flow augmentation.”
The 40x80 and the larger 80x120 test section at NFAC are used to gather data for a wide variety of federal programs. The NFAC team continues to conduct aerodynamic research at large scale on rotor and tiltrotor aircraft, powered lift aircraft, turbine engines and ground vehicles. The facility also provides a full-scale test capability to support a variety of research areas including refueling systems, aero-acoustics and airframe-engine integration.
The end of World War II was still a little more than a year away when the 40x80 made its initial spin. This inaugural operation represented the culmination of years of planning coupled with a relatively quick construction turnaround.
The 40x80 was designed and built by the National Advisory Committee for Aeronautics, an agency founded in March 1915 – a little more than a decade after Orville and Wilbur Wright completed the first airplane flight in December 1903. The N.A.C.A., the predecessor to NASA, was formed to guide American aeronautical research.
In his book “The World’s Largest Wind Tunnels: Their History, Contributions to Aeronautics, and Importance to Flight,” Kenneth Mort wrote the 40x80 wind tunnel was conceived in the 1930s as airplanes were becoming bigger and faster. The N.A.C.A. envisioned the tunnel as a tool to reduce the drag of military aircraft and enhance performance at landing speeds. With the 40x80, committee personnel looked to expand upon what they learned from the construction and operation of the 30-foot by 60-foot wind tunnel built by the N.A.C.A. at what was then known as the Langley Memorial Aeronautical Laboratory, now the NASA Langley Research Center, in Hampton, Virginia.
According to Mort, the 30x60 tunnel, completed in 1931, was initially used for the testing of biplanes and dirigibles, the dominant aircraft of the time. Mort further wrote the tunnel was later used for testing full-scale fighter aircraft and subsequently free-flight models of main aircraft until it was shut down and demolished in 2010.
The second N.A.C.A. laboratory constructed was the Ames Aeronautical Laboratory, now known as the NASA Ames Research Center, at Moffett Field, California. This facility was completed in the late 1930s. It was here that the new 40x80 was to be constructed.
The 40x80 tunnel was designed in 1940 and, by July of that year, foundation piles were driven. The NASA Ames Research Center is located at the southern end of the San Francisco Bay. Due to the conditions of the terrain, these foundation piles had to be driven approximately 200 feet deep.
Actual construction on the 40x80 tunnel began in 1941. Due to the ongoing war, the use of steel was minimized in fabrication of the wind tunnel. Large areas of the pressure shell were made of a cement siding material called transite. The fan blades were made from laminated spruce.
At the time of its construction, the 40x80 was the largest wind tunnel in the world, requiring six 40-foot diameter fans to drive air to a maximum velocity of 200 knots. The maximum velocity of the tunnel eventually increased to 300 knots when the fan drive system was repowered to provide 100 knots in the 80x120 test section.
In his book, Mort provided details on how test were articles placed in the 40x80 tunnel.
“Models were installed in the test section through a pair of double-hinged overhead clamshell doors that opened the full width of the test section,” he wrote. “The doors were 49 feet long, resulting in an access opening at the top of the test section that was 49 feet long and 80 feet wide. A 15-ton overhead crane, which was mounted to the ceiling of the building enclosing the test section, was used for model lifting, handling and installation.
“Typically, models or aircraft were picked up on the shop floor below the test section and lifted about 110 feet overhead, transported over the test section, and then lowered into the test section and mounted on the model-support struts. The models were nominally mounted in the center of the wind tunnel or about 20 feet above the test-section floor. There was also a door in the side of the test section for personnel access and to bring in model access ladders and workstands. Initially, tall ladders were used for model access, but later workstands with wheels were used, which were more stable and safer.”
In its early days, much of the testing conducted in the 40x80 involved fighters and other military aircraft prototypes, according to Mort. After World War II, research was conducted to improve the landing and takeoff performance of aircraft. Later, the impact of wing structure on landing and takeoff was investigated.
“Many of the early experiments performed on aircraft and models determined their basic aerodynamic characteristics and flying qualities,” Mort wrote. “There was a lot of uncertainty in the aerodynamic characteristics of aircraft, and optimum design procedures and requirements had not yet been well established by the aircraft industry. There were significant uncertainties in both longitudinal data and lateral-directional data (side force, yawing moment, and rolling moment). When testing began in the tunnel World War II was still underway, and much of the research was classified as it was war-related with tight schedule requirements. The first few tests were of prototype or experimental aircraft, mostly fighter-type aircraft.”
Test objectives in the 40x80 began to shift as the national manufacturing capability and technology base advanced. With more powerful engines came the development of larger and faster aircraft. According to Sacco, lift augmentation to allow operations from smaller airfields was studied, and the utility of rotorcraft and vertical/short takeoff and landing aircraft became more important to the nation.
Testing in the tunnel would continue to further evolve.
“The increased interest in space science resulted in tunnel research on recovery systems such as parachutes and drag devices, and on spacecraft such as lifting bodies and the space shuttle,” Mort wrote. “Acoustic measurements became important, and after the feasibility of making acoustic measurements in the wind tunnel was established, many wind tunnel investigations included acoustic measurements and studies.”
The 40x80 tunnel was managed and operated by the N.A.C.A. until its dissolution in October 1958, at which point its assets and personnel were transferred to the then-newly formed NASA. These assets included the 40x80 test section, which NASA managed and operated until the NFAC tunnels were mothballed in 2003 due to changing agency priorities.
However, the inactivity at NFAC would be short-lived. In 2005, the Department of Defense opted to resume NFAC operations because of pressing Army rotorcraft research needs, according to Mort.
In 2006, AEDC took on the responsibility of managing and operating the 40x80 and 80x120 tunnels after signing an enhanced use lease with NASA. AEDC personnel developed an updated data acquisition system the following year in order to more efficiently collect test data provided by the tunnels.
“Restoration, repair, maintenance, and checkout testing of the tunnels occurred from 2005 to 2007,” Mort wrote. “Significant work was required to return the NFAC to operational status after years of being offline. The data acquisition system was extensively refurbished, especially to improve data acquisition for rotorcraft experiments. The Air Force implemented a new personal-computer-based system that had been developed at the Arnold Engineering and Development Complex and was based on their experience performing aeronautical research. People with knowledge of the facility were brought out of retirement, and from other Ames organizations, to help manage and guide the refurbishment.
“Operational status was successfully restored in 2007, and the NFAC has been performing a variety of research investigations since refurbishment for the government as well as for many commercial customers.”
The tunnel has been the recipient of various upgrades throughout the course of its 80-year existence. During the 1970s, a shallow sound absorbing liner was installed in the test section. The fan drive was replaced in the 1980s when the 80x120 test section was added at the research facility.
The facility consisting of the 40x80 and 80x120 test sections was dedicated as the National Full-Scale Aerodynamics Complex on Dec. 11, 1987.
A more effective sound absorbing liner and a programmable logic controller control system were installed in the 40x80 in the mid-1990s.
With the 40x80 soon to enter its ninth decade in operation, enhancements to the tunnel continue. Department of Defense Central Test and Evaluation Investment Program funds are currently being utilized to design and fabricate new composite fan blades for the NFAC wind tunnels. An upgrade to the facility data acquisition system is also planned.
To ensure the tunnel continues to operate at an optimal level, the NFAC staff maintains a robust preventative maintenance program to see to it that funding received for 40x80 upkeep and improvements is utilized as efficiently as possible.
“Our staff is very familiar with the facility since the same people conducting the tests do the maintenance and repairs,” Sacco said.
This ongoing care for the tunnel is important, as the 40x80 is expected to continue its role in the development of new technologies well into the future.
“The National Defense Strategy talks about the need to be agile, and the vehicles tested in the 40x80 are at the heart of moving forces and equipment efficiently in an agile manner,” Sacco said.