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.
- ↑ Eastman Jacobs and Ira Abbott note in NACA TR 416 (p. 305) that a serious fire destroyed the tunnel (not the steel shell) in August 1927. The original design had a closed-throat test section five feet in diameter. After the fire it was decided to convert to an open throat design. Jacobs and Abbott reported that this design was not satisfactory. 'The difficulties, which included excessive vibration, unsteady velocity at the test section, a rather large pressure gradient along the axis of the test section, and excessive effects of extraneous air currents on the balance, were overcome by rebuilding parts of the tunnel.' This was wholly unsatisfactory and was immediately replaced with a new closed-throat design. Eastman Jacobs and Ira Abbott wrote: 'The whole interior structure was changed to the closed-throat type. A new exit cone having a smaller divergence angle and a new entrance cone having a better form were built. The synchronous-drive motor was replaced by a direct-current motor. These changes were completed in December, 1930.' (NACA TR No. 416, p. 305)
[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
Don Baals Notes when preparing to write Wind Tunnels of NASA
On a New Type of Wind Tunnel. Max M. Munk.* 1921. TN-60
The Resistance of Spheres in Wind Tunnels and in Air. David L. Bacon and Elliot G. Reid. 1923. Report 185.
Preliminary Wing Model Tests in the Variable Density Tunnel of the National Advisory Committee for Aeronautics. Max M. Munk. 1925. Report 217.
The Variable Density Wind Tunnel of the National Advisory Committee for Aeronautics. Max M. Munk and Elton W. Miller. 1926. Report 227.
The Aerodynamic Characteristics of Airfoils as Affected by Surface Roughness. Ray W. Hooker. 1933. TN-457.
The Characteristics of 78 Related Airfoil Sections From Tests in the Variable-Density Wind Tunnel. Eastman N. Jacobs, Kenneth E. Ward, and Robert M. Pinkerton. 1935. Report 460.
Tests in the Variable-Density Wind Tunnel of Related Airfoils Having the Maximum Camber Unusually Far Forward. Eastman N. Jacobs, and Robert M. Pinkerton. Report 537.
- See also Max Munk Archives Collection