14 X 22-Foot Subsonic Tunnel
|Center:||Langley Research Center|
|Historic Eligibility:||National Register Eligible|
In the 1950s, the NACA began conducting exploratory research on radical new vertical take-off and landing (VTOL) aircraft. Wind-tunnel tests of VTOL configurations require facilities with relatively large test sections compared to the model size in order to avoid contamination of aerodynamic data due to wall effects. Such configurations use large turning of the airflow, especially in accomplishing the transition from helicopter-like hovering flight to conventional forward flight. Artificially flow-constraining and flow-deforming effects of tunnel walls cannot be tolerated in VTOL tests. At Langley, early VTOL tunnel testing was conducted in the Langley Full Scale Tunnel and the Langley 300-mph 7 X 10-Foot Tunnel (1212A). The 7 X 10-Foot tunnel was subsequently modified in an attempt to accommodate VTOL model testing by installing a larger 17-foot test section in its entrance cone to reduce wall effects. However, both the full-scale and modified 7 X 10-ft tunnels were limited by relatively low values of test Reynolds number and general flow quality. In 1967, a proposal was made to NASA management for a more capable new wind tunnel specifically designed for vertical and short take-off and landing (V/STOL) configurations. The proposal, initially known as the V/STOL Transition Wind Tunnel, was ultimately accepted and construction began in 1968 with the demolition and removal of the 7 X 10-Foot Tunnel (Building 1212A).
The new Langley V/STOL Tunnel (Building 1212C) was built partially on the site formerly used by the 7 X 10-Foot Tunnel, and it began operations as a single-return atmospheric wind tunnel with a rectangular test section in 1970, featuring removable side and top walls to minimize tunnel wall effects for various types of tests. It could also be operated in a closed test section mode with slotted walls. In the closed test section configuration, the maximum airspeed was approximately 230 mph. The test section was 14.5-feet high by 21.75-feet wide and approximately fifty feet long. The tunnel also was fitted with a removable endless-belt moving ground board installation capable of realistically simulating landing conditions up to two hundred knots. The test section airflow was produced by a forty-foot diameter, nine-bladed fan powered by a 6,650-horsepower alternating-current induction motor in tandem with a 1,350-horsepower direct current motor. The tunnel also has a unique set of controllable flow vanes which are used for precise speed control at low speeds. Acoustic measurements for rotorcraft and other powered models were provided by raising the test-section walls and ceiling and by treating the floor and ceiling with acoustic-absorbent material. Laser velocimeter equipment was also installed to enable precise flow measurements over models of aircraft and rotorcraft. Extensive flow visualization equipment is available.
Models can be powered with either high-pressure air or variable-frequency electric systems, and model preparation is made more efficient by mounting them on carts prior to tunnel entry.
The name of the Langley V/STOL tunnel was changed to the Langley 4 X 7-Meter Tunnel in the early 1980s when NASA stressed the use of the International System of units and renamed a number of facilities. A major facility upgrade was accomplished in 1984 when modifications were installed to improve the tunnel flow quality and further expand its capabilities for acoustic and rotorcraft testing. In the early 1990s the name of the tunnel was again changed to its current designation of the Langley 14 X 22- Foot Tunnel. Further improvements to the facility have included a new tunnel test automation system, new model carts in 1999, and replacement of the main drive motor in 2001.
As one of the premier low-speed wind tunnels in the NASA inventory since its opening, the 14 X 22-Foot Subsonic Tunnel has been the site of a broad range of aerodynamic tests for NASA, industry, DoD, and academia including aircraft, rotorcraft, structures, and various types of ground vehicles. In addition to regularly scheduled test programs, the tunnel has also been adapted for specialized test previously conducted in the Langley Full Scale Tunnel including free-flight tests and forced-oscillation tests.
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