ARNOLD AIR FORCE BASE, Tenn. --
The hardware making up the Arnold Engineering Development Complex Tunnel E facility has been scrapped, leaving behind a mostly empty room in the building that also houses Tunnel D at the von Kármán Gas Dynamics Facility at Arnold Air Force Base.
It hasn’t been an active wind tunnel in years, so the very existence of Tunnel E is not known by many current AEDC employees.
Before the Tunnels B and C were up and running, Tunnel E, first named Tunnel E-2, was used as a pilot facility. It originally operated in 1959, six years after neighboring Tunnel D, previously Tunnel E-1, first ran as a pilot facility for VKF Tunnel A.
“Like Tunnel D, Tunnel E operated as a pressure-vacuum blowdown wind tunnel using high pressure air and the VKF 72-foot vacuum sphere to supply the required pressure ratios across the nozzle and test section,” said Dr. Jerrod Hofferth, a research aerospace engineer with the Air Force Research Laboratory at Arnold. “Heating of the air supply, up to 1,000 degrees Fahrenheit, was provided by a 4.5 megawatt inline electric-resistance heater.”
Initially, Tunnel E was equipped with a 12-inch by 12-inch flexible-wall nozzle providing test section Mach numbers of 5 to 8. The flexible plate was made from a beryllium-copper alloy and water-cooled. The typical run times were 5 to 10 minutes in this configuration.
In 1967, the facility was reconfigured with a fixed-geometry, axisymmetric 13.25 inch-diameter Mach 8 nozzle in part to accommodate a novel traversing magnetic model support system, or MMSS.
“The MMSS system allowed a test article to magnetically levitate in the center of the test section and be moved forward up to 40 inches during a run in order to eliminate support interference while performing wake surveys behind re-entry vehicle geometries,” Hofferth said. “With this system, a single probe rake or schlieren optical setup could measure the wake several body diameters downstream of the test article in a single run.
“The electric current required to maintain position in the wind tunnel was monitored and calibrated to provide measurements of lift, drag and yaw forces, as well as pitching and yawing moments. Angles of attack and sideslip were measured with X-ray imaging of the iron-core test articles through aluminum test-section walls.”
Like Tunnel D, the Tunnel E facility was decommissioned sometime in the late 1970s.
Hofferth explained that by the time the AFRL team arrived at Arnold AFB in 2015, all that was left of Tunnel E was the 4.5 megawatt electric heater and legacy process air control valves.
“The key parts of the high-speed wind tunnel architecture, such as the nozzle, test section and magnetic model support system, had all long-since been excessed,” he said. “The magnetic model support system had gone to NASA Langley in 1979 and was used for some time in a subsonic facility, but no longer exists today.”
After a joint AFRL and AEDC technical assessment, it was determined that the heater, process air controls and related support systems were likely not viable as components of any future facility development to be undertaken by AFRL, so a demolition project was begun to reclaim the 25-foot by 50-foot space to support AFRL research activities.
In the near future, the resulting increase in space will be utilized in support of ongoing AFRL research operations in Tunnel D, which is the 1-foot supersonic research platform made fully operational by an AFRL reactivation and modernization project between 2016 and 2018. AFRL researchers and support contractors will use the additional space for model build up and prep, light shop work, diagnostics development and other work.
“Looking out further, however, AFRL does envision an opportunity to again use the test bay for a modern aerodynamic research facility with capabilities complementary to those afforded by Tunnel D,” Hofferth said. “A new facility designed to suit research needs could leverage the existing high-pressure air, vacuum, and data systems put in place for Tunnel D during its reactivation.”