Variable Density Tunnel
|Center:||Langley Research Center|
|Historic Eligibility:||National Historic Landmark|
|Important Tests:||Early aircraft development|
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The Variable Density Tunnel (VDT) played a major role in U.S. aircraft development in the first half of the century. It was an important tool in the revolution of aircraft design that occurred between 1923 and the outbreak of World War II. The VDT was conceived in 1921 by Dr. Max Munk, an early technical employee of NASA's predecessor, the National Advisory Committee for Aeronautics (NACA). Within two years, this revolutionary piece of experimental test equipment went in to operation.
The pressure shell of the VDT was fabricated at the Newport News Shipbuilding and Dry Dock Company in 1921 and completed in February 1922. It was transported from that facility to NACA by barge, arriving in June of 1922 for installation in what is now known as Building 582. The history of The Arrival of the Pressure Tank was reviewed in 2010 and some long-held myths were dispelled. The VDT tank is 34.5 feet long by 15 feet in diameter and is made of boiler plate steel more than two inches thick, weighing in at 85-tons.
The VDT yielded test results so superior to that obtained with any previous wind tunnel, especially regarding airfoil design and performance, that NACA became the acknowledged world leader in aeronautical research.
Originally located in Building 582 in the Center's East Area, the VDT was partially destroyed by fire in 1927 and was rebuilt and operational again by 1930. By the 1940's the tunnel was obsolete and was gutted. It was then used as a pressure tank to support the operation of the Vertical Spin Tunnel and the Low Turbulence Pressure Tunnel. The VDT continued to serve in this capacity until it was declared unsafe for further operation in 1978.
The office space in the structure that was the original home to the Variable Density Tunnel was used through the 1990s. It was anticipated that the Air Force would take ownership of the building once NASA vacated the premises. Once they indicated the building would not be needed, plans were begun to demolish the structure. It was demolished in 2014. The stone door header and the stone NACA wings were salvaged and will be incorporated into the pressure vessel display.
As part of the "Man in Space" theme study that was performed by the National Park Service in 1984, the VDT was declared a National Historic Landmark in 1985 for its contributions to the development of flight. In 1991 it was relocated to the West Area and remains on display in its current location adjacent to the Reid Conference Center.
[top] Tunnel Descriptions
The following information was provided by Ken Pierpont in a writing he put together in May 1977.
- Variable Density Tunnel (VDT) - also known at Wind Tunnel #2 and the Compressed Air Tunnel; built as closed throat with 5-foot diameter test section; rebuilt about 1928 after a fire with a 5-foot diameter test section with an open throat
- 12-Inch High Speed Tunnel - August 1927; built as open throat tunnel operating as induction blow down from VDT
- 11-Inch High Speed Tunnel - also known simply as the High Speed Tunnel; 1929-1932, superceded by the 12-Inch High Speed Tunnel; induction blow down tunnel with closed throat
- Model Water Tunnel - 1928-1931
- NACA 2-Foot Smoke-Flow Tunnel - 1928-1931 also called the Demonstration Tunnel
[top] 11-Inch High Speed Tunnel
This tunnel was used for investigating the aerodynamic characteristics of propeller blades and other bodies moving through the air at high speeds. The velocity of sound was used as a basis of reference in this work. The balance and tunnel test section were housed in the chamber at the center.
[top] 24-Inch High Speed Tunnel
[top] 2-Foot Smoke-Flow Tunnel
Air-flow studies by direct observation have proved to be of great value, but owing to the difficulty of making air flows visible, this method of investigation has not been widely used. The smoke-flow equipment using titanium tetrachloride smoke, was designed to make such investigations. An unusually steady air stream is provided, in which the models are placed. The flows are observed or photographed though a glass window forming the one side of the air passage. (photo caption)
[top] VDT Removal in 1989 and Exhibit Dedication 1991
[top] Research Papers
The Aerodynamic Characteristics of Airfoils as Affected by Surface Roughness (TN-457). Ray W. Hooker. 1933.
The Characteristics of 78 Related Airfoil Sections From Tests in the Variable-Density Wind Tunnel (Report 460). Eastman N. Jacobs, Kenneth E. Ward, and Robert M. Pinkerton. 1935.
Tests in the Variable-Density Wind Tunnel of Related Airfoils Having the Maximum Camber Unusually Far Forward (Report 537). Eastman N. Jacobs, and Robert M. Pinkerton.