Variable Density Tunnel

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Facility 582
Tunnel in 1922

Center: Langley Research Center
Location: Hampton, Virginia
Year Built: 1922
Historic Eligibility: National Historic Landmark
Important Tests: Early aircraft development

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[top] History

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 [1]. 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 1989, it was removed from Building 582, relocated to the West Area and placed on display adjacent to the Reid Conference Center (Building 1222). See photos below, VDT Removal in 1989 and Exhibit Dedication 1991, showing the relocation process. With construction of the new Integrated Engineering Services Building (Building 2102) which houses the new Reid Conference space, Building 1222 was demolished in 2019. The VDT was again relocated to a location adjacent to Building 2102 within the central core of the Center. See photos of the relocation below.

Variable Density Tunnel

[top] References

  1. 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] Photos

[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)

NACA 7088.jpg

[top] VDT

1921 Tunnel Model1921 Tunnel Model1920 AerialWT 010a.jpgFeb 1922 Pressure Shell of the VDT at the Newport News Shipbuilding & Dry Dock CompanyEL-1999-00253.jpg1921 Inside of Building before ConstructionVDT HousingEL-1999-00255.jpegEL-1999-00254.jpgWT 006.jpg1922 Tank on Barge56b.jpgJune 1922 Arrival at Langley1948-10-28 Air Scoop, 1922 Turner and Gardner in Front of VDTWT 007.jpgWT 005.jpgWT 010b.jpg1922 Dr. Munk by the Tank1926 Dr. Max Munk at his officeWT 008a.jpgWT 008b.jpgWT 62.jpg1921 Interior View after CompletionWT 54.jpgWT 61.jpgWT 55.jpgWT 59.jpgWT 60.jpgWT 53b.jpg1922 Honeycomb SectionsWT 64.jpg1922 Balance Ring1922 Aerodynamic Meeting of NACA1922 Inside the VDTPropeller in Test SectionTunnel EquipmentPropeller Closed ThroatTunnel Drive ShaftPropeller Open ThroatTunnel Screen FullTunnel Screen AperturePropeller Open Throat Full PictureTunnel Test EquipmentView of Model Test1922 Interior of Test CellShell1922 Internal Frame1922 Pressurizing Equipment1922 Tunnel Entrance1923 Control Panel1923 Interior of Building1923 Motor and Drive Shaft1923 Test Researcher1923 Underside of Tunnel19231924 Test Observation1925 Installing 35B Airfoil Test Section1927 FireTunnel Screen1927 FireTunnel ExteriorEnd of ShellInside the VDT1928 DiagramSchematicOpen Throat SchematicModified Closed Throat SchematicClosed Throat SchematicLMAL 40111.jpgLMAL 40112.jpgLMAL 40113.jpgLMAL 40114.jpg1929 Control Panel1929 Control Panel1929 Test1929 VDT during testingExterior ViewEntrance (taken 2011)Lintel (taken 2011)NACA Wings (taken 2011)2012 Complex Components2012 Floor Plan

[top] VDT Removal in 1989 and Exhibit Dedication 1991

89-12626.jpg89-12631.jpg89-12635.jpg89-12640.jpgAdditional Photos

[top] VDT Relocation in 2019

On March 2, 2019, the VDT was moved to a higher visibility and more accessible location on center. The VDT's new home is located between the Integrated Engineering Services Building (IESB; 2102) and Building 1219. The new location is at the centers main pedestrian walkway where the National Historic Landmark will be more accessible to employees and visitors. To view photos of the relocation process, click "HERE"

[top] Films

Study of Flow in Open Throat Tunnels

[top] Documents

[top] Building

1921 Floorplan

1924 Longitudinal Section

1924 Sectional Showing Cones and Balances

1926 Preliminary Wing Model Tests in the Variable Density Tunnel

1938 Floorplan

1933 The NACA Variable Density Wind Tunnel

1942 Construction Information

1942 Quick Facts on the Variable Density Tunnel

1984 National Park Service "Man in Space" Theme Study

1984 National Historic Landmark Nomination Form

1986 National Register Survey Form

1989 Report on Considerations in Moving VDT

1989 Letters Discussing Relocation of Variable Density Tunnel Pressure Vessel

1989 SHPO Response Regarding Moving VDT

1989 LaRC Response to SHPO

1991 Exhibit Dedication Plan

1991 Site Plan for Exhibit

1991 The Variable Density Tunnel

1991 Wind Tunnel Becomes National Landmark

2010 Joseph Chambers: A Critical Look at Langley's History: The Arrival of the Pressure Tank of the Variable Density Tunnel at Langley

National Park Service Web Site

Paragraph Published in Virginia Landmarks Register on the Variable Density Tunnel

[top] Research Papers

Log Book

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.

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