Major upgrade project in AEDC's propulsion wind tunnel complex reaches a milestone

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  The modernization of the Propulsion Wind Tunnel Complex's (PWT) 4-foot Transonic Wind Tunnel (4T), which first became operational in 1967, is now at a critical juncture.

"We will be shutting down operations in Wind Tunnel 4T for a 20-month investment outage starting in October for a major upgrade, said Steve Pearson, ATA general manager at the Arnold Engineering Development Complex (AEDC). "This test unit will receive a new data system, captive trajectory system (CTS), flex nozzle actuators and controls, roll system and new diffuser seal flaps. The tunnel is scheduled to return to service in June 2014. While we will lose the capability to serve customers with 4T, it is exciting to see this level of investment, which will greatly improve the test capabilities and reliability of the tunnel."

Peter Macaluso, AEDC's project manager of PWT, is excited about the current milestone the project's team has reached with 4T's modernization program.

"[Since] we've got a few years of planning already under our belt, we're now to the point where we're going to start turning on the torches, cutting holes and wires and this is where all of our planning will pay off," he said. "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."

Macaluso said to appreciate the significance of this stage of the facility's modernization, it is imperative to know what takes place in this unique national ground testing asset.

"4T is an aerodynamic wind tunnel," he said. "It is the premiere 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."

Macaluso explained the testing process in 4T.

"We call what is mounted on or in the aircraft a 'store,' whether it's a bomb, missile, extra fuel tank, camera pod or whatever," he said. "The typical store test in 4T includes both store configuration testing and store separation testing on small-scale models of the aircraft and stores."

As the technology and capability of military aircraft continues 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.

Data Acquisition System

Since accurate and time sensitive data is critical to any test at AEDC that part of the modernization is being addressed by a major upgrade to 4T's data acquisition system. This will include switching to TestSlate© software, 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."

Upgrade of the Captive Trajectory (CTS) System

The CTS 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 percent, 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."

Macaluso said their design team has also researched the use of robotics used by auto manufacturers and incorporated state-of-the-art gear drive technologies.

Modernization of flex nozzles actuators and controls

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 electro-mechanical 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.

Fox, an engineer who has worked primarily in the von Kármán Gas Dynamics Facility Tunnels A, B and C and PWT for 20 years, said, "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."

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 to 4T

Macaluso said other aspects of the facilities upgrade are equally important to meeting the customer's current and future requirements. These improvements include:
  • The 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.

John Laviolette, AEDC's test systems acquisition project manager on the 4T modernization, said the project has been very challenging due to the complexity of the test components, demanding test requirements and age of the existing facility.

Laviolette credits the team effort on the project as being essential to its success so far.

"The collaborative efforts between the various divisions within ATA have just been fantastic from the onset of this project," Laviolette said. "From planning, design and fabrication, they've taken the lead. The team has worked hand and glove with the managers and craftsman at the model shop and the machine shop to be able to fabricate many of the components which require a high degree of precision to meet time constraints or competing priorities.

"ATA met the challenge both logistically and technically to fabricate and obtain the thousands of components necessary for the project."

Laviolette added, "This has really been a team effort from day one. It's really exciting to really see it all come together to plan and prepare for this major facility outage."