One of the transonic wind tunnels at the Propulsion Wind Tunnel (PWT) complex at Arnold Air Force Base, TN, was recently shut down to undergo a major upgrade, to include a new data system, captive trajectory system (CTS), flex nozzle actuators and controls, roll system, and new diffuser seal flaps. The 4-ft Transonic Wind Tunnel (4T), which first became operational in 1967, is scheduled to return to service in June 2014.
“The 18-month outage will be followed by return-to-service testing to validate all of the systems before the customer can return to conduct their testing,” said Peter Macaluso, Arnold Engineering Development Complex’s (AEDC’s) project manager of PWT. “[4T] is the premier weapon separation tunnel for the United States and the foreign governments we support in our mutual interest. Most of our customers, who come to tunnel 4T, are here to conduct a wind tunnel weapon separation test.”
The typical test in 4T includes both store configuration testing and store separation testing on small-scale models of the aircraft and stores. Stores include anything mounted on or in the aircraft, whether it’s a bomb, missile, extra fuel tank, camera pod, etc.
As the technology and capability of military aircraft continue to advance, a modernization goal for 4T is to match the facility’s range of test capabilities for today’s customer and those of the future.
4T’s data acquisition system is receiving a major upgrade, switching to Test SLATE software from Jacobs, which was recently installed in the von Kármán Facility (VKF) upgrades.
After the software passes trial implementation, it would allow for time stamping of data at the point of acquisition. The system also promises to integrate several independent data systems and have higher data acquisition and processing rates.
“Once validated, this commonality will allow a seamless transition for customers who wish to test flight systems from subsonic to transonic speeds in Tunnel 4T and then bring the model to VKF to continue testing the same model from transonic speeds to high supersonic speeds,” Macaluso said. “Before, hours of programming were required to set up for testing in 4T and then again in Tunnel A. Soon it should be much faster and will only have to be performed once.”
The CTS being installed is a six degree-of-freedom system permitting staging or store separation studies in either grid or trajectory modes of operation. The upgraded system will have significantly increased position accuracy.
“Another important aspect of the CTS upgrade includes an increased load capacity by approximately 40%, to enable the tester to accommodate those larger store models,” Macaluso said. “We’ve met the challenge of reducing the air flow blockage associated with this increase in larger store loads.”
When the project is completed and verified by testing, the new flex nozzle and actuators will be equivalent to the system already incorporated into AEDC’s hypersonic, continuous flow ground testing asset, the von Kármán Gas Dynamics Facility’s Tunnel A.
This will improve reliability and position accuracy of the electromechanical actuators that are used to shape the flexible plate to set the required nozzle contours, according to AEDC’s Greg Fox, ATA’s section manager over flight systems operations and maintenance.
“This is how flow conditions are set in the wind tunnel to simulate the conditions encountered by an aircraft in flight when its associated stores are mounted in an internal bay or on wing pylons, or when the pilot releases those stores during the execution of a mission,” said Fox, an engineer who has worked primarily in the von Kármán Gas Dynamics Facility Tunnels A, B, and C and PWT for 20 years.
Other changes will include improved system reliability, along with commonality with Tunnel A, and all systems will have an air-on acceptance as part of the validation schedule for 4T’s checkout.
Fox said increased reliability translates to less downtime for repairs, which allows for a higher throughput of testing in 4T.
Other improvements include:
• Test section walls have been strengthened to allow for testing up to Mach 2.46.
• Installation of a modernized main electrical distribution system, installation of a new roll mechanism providing enhanced accuracy.
• Modernization of translational seal flaps used to reduce turbulence by covering the “holes” left when the support holding the aircraft model comes up through this opening.
“The support system for the store, the CTS hardware, is in the ceiling, and a flap covers the hole left by the CTS as it moves forward and backward,” Macaluso said.