The Propulsion Wind Tunnel Facility, located at Arnold Engineering Development Center, Arnold Air Force Base, Tenn., holds three wind tunnels -- the 16-foot transonic (16T), 16-foot supersonic (16S), and the aerodynamic 4-foot transonic (4T). 

The facility is devoted to aerodynamic and propulsion integration testing of large-scale aircraft models.  Basically, PWT provides AEDC customers with complete testing and analysis capabilities.  

Some of the most powerful electric motors ever built are located in the PWT facility.  In fact, PWT is as tall as a two-story house and as heavy as a railroad locomotive.  

In addition to 16T, 16S and 4T the PWT facility provides customers the following capabilities: Store Separation Testing, Pressure Sensitive Paint Capability, and Captive Trajectory Support Testing.  AEDC also provides a wide range of computational support to the test and evaluation process that impacts how the U.S. Air Force, U.S. Army, and the U.S. Navy develops new weapon systems. 

Propulsion Wind Tunnel 16T.  The facility has two 16-foot by 40-foot long test section, closed-circuit wind tunnels.  One is transonic (16T), one is supersonic (16S).  

16T can be operated from Mach numbers 0.06 to 1.60.  16S is currently inactive, however, when it was operational it could operate from Mach numbers 1.60 to 4.75.  

Both tunnels, 16T and 16S, are utilized for conventional aerodynamic tests, combined aerodynamic/propulsion systems tests, and a array of other tests. 

Aerodynamic Wind Tunnel 4T.  The four-foot aerodynamic wind tunnel is PWT's versatile, midsize test unit that has a four-foot by four-foot by 12.5-foot long test section.  The transonic designation indicates its primary utility is for testing from subsonic to low end supersonic airspeeds.  Its capability is roughly equivalent to an airspeed range from 160 to 1,600 miles per hour.

Store Separation Testing.  Store Separation Testing ensures bombs, missiles, drop tanks, or other stores separate cleanly from the parent aircraft when released.

At transonic speeds, certain altitudes, or manuever conditions, the aerodynamic forces on a store may cause separation from the aircraft. When the separation occurs, it must happen cleanly, if not the store will veer upward when released and collide with the aircraft. In years past, bombs were carried and dropped out of bays. However, as high thrust engines became available, the weapons could be shifted outside and carried in considerable numbers on pylons attached to the lower surface of the wings, as well as in bays. Problems became evident when the aircraft speed became progressively faster.

The dynamics of clean store separation (investigations of aerodynamic forces that can alter the planned projectory of air launched bombs or missiles) are explored in 16T and 4T.  The aircraft model is mounted upside down in the tunnel on a strut.  The store model is mounted on a special moveable support system called a sting attached within the test section and positioned very close to the aircraft as it would be in flight. 

When the desired simulated flight conditions are established in the tunnel, the store model is 'launched' from the parent aircraft model by activating a computer that controls movement of the sting-supported store as it traces the trajectory.  Information obtained in these tests is used to design new stores or to modify carriage and release mechanisms to make sure they separate cleanly, do not damage the parent aircraft, and stay on the intended flight path in the proper altitude.

Captive Trajectory Support Testing.  The CTS systems for AEDC's wind tunnels allow computer-controlled, six-degrees-of-freedom positioning of a missile, bomb, or any other store in close proximity to the aircraft model.  Operational CTS systems exist in tunnels 4T and 16T.  Applications in the PWT transonic and supersonic test units consist of store separation and flow-field mapping.

Pressure Sensitive Paint Capability.  AEDC utilizes the Pressure Sensitive Paint technology to determine the surface pressure at several hundred thousand locations on wind tunnel models.  

Before testing begins, a special paint and illumination source is applied to the test model in two layers - a white undercoat and the PSP layer.  The white undercoat provides a uniform reflective surface for the PSP layer.  

During a test, an extremely sensitive camera obtains the surface pressure data when the illumination source excites the PSP layer.  

However, it is important to note that pressure orifices cannot be installed in some areas of the model (i.e. thin surfaces) which limits the measurement of surface pressure. 

16T has a multi-view PSP data acquisition system.

In January 1950, planning for the PWT began when the Air Force Research and Development Board on Facilities met with representatives of aircraft propulsion companies. During the meeting, the group agreed that industry needed a supersonic PWT with a 15-foot-diameter test section.

After much work, a proposal for design, construction, and operation of a scale model of PWT's transonic circuit was approved by AEDC's commanding general in December 1951. Thus, the initial test facility was a one-foot cross-section prototype transonic tunnel. In June 1953, AEDC conducted PWT's first test on a 0.03-scale model of the Bomarc missile for Boeing.

In 1956, the transonic circuit - 16-foot test section - underwent its first powered operation prior to calibration.

By January 1961, the entire PWT complex was completed and accepted by the Air Force. The entire project cost was $78.7 million, which was spread out over 39 contracts.

The PWT Facility has conducted a number of tests since its opening. In 1989, the American Society of Mechanical Engineers designated PWT an International Historical mechanical Engineering Landmark. 

Over the years, AEDC has worked hard to ensure the viability and accuracy of its test facilities.  The center had a multi-view PSP data acquisition system installed in 16T during 1999.

In 2005, the Air Force funded Propulsion Wind Tunnel Sustainment Program provided AEDC with $80 million to upgrade PWT with the 21st century testing technology.  Completion of these improvements fully automated the PWT facility.