AEDC leads the way with new testing capability for smaller gas turbine jet engines

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A small, but dedicated team of engineers, machinists and craftsmen have completed a reactivation project on Arnold Engineering Development Center's T-3 engine test cell, significantly expanding the center's test capabilities.

"We're very excited about having T-3 ready for test operations," said Jonathan Osborne, an Aerospace Testing Alliance analysis engineer on the project. "T-3 can now simulate an altitude of up to 100,000 feet and a Mach number up to 4.1."

Williams International is tentatively scheduled to bring an XTE88 low bypass ratio, afterburner-configured turbofan jet engine for testing at AEDC between October and December 2008, he said.

Simon Choi, the center's Air Force investment program manager, emphasized the team effort it took and complexity involved in getting T-3 ready in time for mission-critical testing slated for later in the year.

"This was a combined investment and maintenance projects effort to reactivate, upgrade, and perform checkouts of the T-3 test cell and to have the reactivation completed successfully on-time and on-cost was no small feat," he said.

"This impressive effort involved upgrading and repairing facility support systems, T-3 instrumentation and new data systems, reconfiguring power-plant air and temperature control systems and valves as well as heaters, liquid air, fuel and cooling water systems.

The objective of the checkout tests was to determine, demonstrate, and document the maximum envelope of the facility's capabilities, handle unforeseen issues and upgrade a significant amount of unused plant equipment and systems.

"Our investment and maintenance people did an excellent job of working together to plan and execute these efforts. Unlike an ordinary investment project, this one required technical expertise from our test and evaluation team as well as knowledge of structural, instrumentation and complex plant controls, backed up by plenty of dedication from all of us."

Dr. Charles Vining, the 717th Test Squadron Technical Director, shares Osborne and Choi's enthusiasm for the successful reactivation of T-3 and also emphasized the importance of the facility's improved capabilities.

"Simulated altitude testing in the T-3 test cell is an essential step in the development of the High Speed Turbine Engine Demonstration (HiSTED) Mach 4-plus turbine engine," he said. "The operating conditions are both extreme and beyond current experience presenting a unique set of challenges for ground testing.

 The T-3 test team has completed the initial demonstration of T-3 and has the expertise needed to meet the challenges of the upcoming test."

Osborne, who directly supports T-3 test operations, including the recent and successful validation and checkout tests on the facility, said they are ready to test the XTE88 slated to arrive at AEDC later in the year.

DARPA Tactical Technology Office Deputy Director Dr. Steven Walker, commenting on the importance of HiSTED and Arnold's reactivated facility said, "Evaluating and validating the XTE88 engine and ones like it is critical for the Defense Advanced Research Projects Agency's (DARPA) High Speed Turbine Engine Demonstration (HiSTED) program.

The team at AEDC will be conducting simulated altitude testing in T-3 to help demonstrate engine performance and provide operability characteristics at key transonic and maximum Mach/altitude cruise flight conditions. The improved capability of T-3 will be the key to this effort."

Williams International High Mach Propulsion Director Mike Bak agreed and said T-3 is a vital resource for the upcoming testing and what may follow.

"This facility is a must have if we go to flight test with this class of engine," he said.

"The risk of operating over this wide range of flight conditions without a propulsion wind tunnel test would be extremely high for a flight test vehicle that will cost hundreds of millions of dollars.

We are excited to have the capability to test across the flight envelope of the XTE-88 engine."

Stephen Sepeck, the Air Force Research Laboratory (AFRL) propulsion branch project engineer on the upcoming HiSTED program test, came to AEDC late last year to monitor the progress being made to reactivate and validate T-3.

"We were looking at that checkout to see if the test cell could get to the performance points that we needed to when the engine comes," he said. "We were trying to hit a Mach 4 test point with a turbine engine.

The reason that we wanted to come here was T-3 is the only test cell that has the capability to move relatively quickly from one test point to another test point in more of a missile profile mode."

Osborne said prior to the recent reactivation, T-3 has had only limited use over the years, mainly because of financial constraints.

"T-3 was developed in the early 1990s with the intent of supporting small turbine engines, but funding got cut and the existing test cell systems were used to support Siemens Westinghouse Combustor rig testing," he explained. "The rig was used for testing commercial turbine engine combustors."

After 2004, an increased interest from the Department of Defense and industry in what the specialized test cell's potential capability could deliver and new funding had allowed the team at AEDC to engage on the reactivation project.

"It was then that we started reconfiguring the test cell back to where we could support small, very fast (jet) engines, mainly for the HiSTED engine programs," Osborne said. "We have high Mach test facilities, but T-3 is unique in the fact that it's not a vitiated test cell. In T-3 we're running what we call clean true air; there are no combustion products in the air supply."

Eliminating these contaminants from the air flowing through an engine gives a more accurate picture of the test article's performance and a better idea of how the engine would perform in flight, he said.

"This is something that our customers will always want; if the engine can fit into the size limitations of this facility, we can off them the high altitude/high Mach portion of the flight envelope they need."

Regarding the upcoming testing on the Williams International XTE-88 engine, Bak explained why the T-3 test facility is well suited to the project.

"All the air that comes into our engine inlet is processed through the engine and afterburner," he said. "Test cell T-3 has the capability to provide the full enthalpy inlet conditions to the engine with non-vitiated air.

The NASA Propulsion Systems Laboratory tunnel uses inline combustors to heat the air with oxygen replenishment which changes thechemistry of the inlet air supply. T-3 also has the capability to change inlet temperature and pressure to the engine at a rate fast enough to simulate the trajectory of the flight vehicle which will be beneficial for evaluation of the engine and its control system."

Osborne drew a comparison and contrast between how T-3 and the larger engine test cells operate at the center.

"We run T-3 just like any other direct-connect turbine test cell on base, like C-1 and C-2 in the Aeropropulsion Systems Test Facility (ASTF)," he said. "In the Aerodynamic and Propulsion Test Unit (APTU), a free jet test cell at AEDC, they currently run up to Mach 6, but they burn isobutane in the airstream to get the temperature up. In T-3 we have big, natural gas-fired heaters that raise the inlet temperature up to 1,200 degrees or so, which eliminates the need to burn fuel in the airstream.

That gives us the temperature we need plus the pressure we get from the von Karman Facility or C-Plant."

Osborne said his team verified T-3 was operational last year, with the most recent checkout test conducted in January 2008. He pointed out that the operating conditions in the high Mach engine test cells, whether conducted in APTU or T-3; all have one thing in common - they are volatile.

"We've had a lot of upfront stress analysis completed on the system to make sure that it will be able to handle the high temperature and pressure conditions," he said.

 "Getting T-3 ready has been very challenging. With these high Mach input conditions, we've got 1,200 degree air coming into the inlet at a potentially high pressure. That causes the ducting to start moving towards its' material limits."

He said the project's design people ran T-3 through a range of operating conditions, including the most extreme conditions to ensure the ducting will not fail.

"We have to make sure we don't over-pressurize the system to where it could potentially rupture," Osborne said "That was a pretty big challenge. The inlet ducting going into the test cell is hot, I mean broiling hot. As with any experiment, there's always a possibility of failure, but it was all well planned thought through and we had successful test periods. The only problems we experienced were just your normal issues, valves not working right and things like that, but you can get that with any test cell."

The first phase of the reactivation effort on T-3 began in 2003, according to J. Ray Joellenbeck, the facilities mechanical installation and test engineer.

"It focused on reactivation of the test cell and all the standard support systems such as the fuel system, nitrogen system, service air system and raw water system, etc.," he said. Most of these systems were either removed or greatly modified to support the Siemens Westinghouse combustor rig testing."

Budget and schedule restraints prevented a full demonstration of the facility's capability at the time.

"Our first turbine engine test, which followed the first phase of reactivation in 2005, didn't require the full capability of T-3 since it was only operated at fairly benign inlet conditions," Joellenbeck said.

Beginning in 2006, the second phase of reactivation focused on defining the test cell's operating envelope.

"The work mainly focused on the analysis of the plant process air supply and the T-3 inlet air mixer as well as reinstallation of the diffuser to allow us to operate near 100,000 feet simulated altitude," Joellenbeck explained. "Steve Kinard, a Jacobs Engineering design engineer, was instrumental in the analysis of the process air system and air mixer to verify we could safely operate at the 1,300 degree Fahrenheit design condition.

From his perspective as a test engineer, Joellenbeck finds the operational capability of T-3 something he has had to adjust to from previous experiences with engine test cell environments.

"To operate T-3 I had to recalibrate my thinking of what 'extreme' flight conditions are," he acknowledged. "In the past, I would have considered a 300 degree (Fahrenheit) inlet to be very extreme and very rarely done. Now, the standard T-3 test will operate near 500 degrees as the jumping off point for a hot run up to 1,200 degrees and then cool back down between 300 to 400 degrees. You have to take a whole new look at operations when your inlet is still near 600 degrees the day after your test."

Sepeck, AFRL Propulsion Branch project engineer, said a lot is riding on the success of the upcoming HiSTED test.

"If we can hit our points we will prove that the engine would fulfill the mission it's going to be designed for," he said. "It's very complicated - I've sat through three tests now. We've had various problems, but I was impressed with Ray Joellenbeck and Mark Cross's ability to do the work arounds to achieve their run plan for the day. They did what it takes to overcome some obstacles to get their testing accomplished and make our points. I was impressed with their knowledge."

Sepeck credited the team at AEDC for going beyond getting the test cell up and running to the required performance levels for upcoming testing tentatively slated for the October to December time frame.

"Along the way they made improvements each test period," he said. "They fixed the
 problems they had before and we were able to cut some time out of the run ups.

Eventually, that will probably save us some run time once they get all the kinks worked out and know how to get there efficiently, which will save the customer some money."

Joellenbeck agreed with Sepeck's assessment, saying, "There are still more challenges ahead. Even though we have proven we can safely operate T-3 at these extreme conditions, we look forward to the new challenges that come with the installation and operation of test-peculiar support systems and the test article at these conditions. These challenges, working with cutting-edge technology and doing something that no one else has done before is what makes my job fun."

Caption for 070409-O-0000U-001: From left (foreground) Aerospace Testing Alliance (ATA) boilermakers Allen Gardner, Rusty Hargis and Don Metcalf install the diffuser insert in the T-3 exhaust duct. (Photo by Ray Joellenbeck)

Editorial Note
Arnold Engineering Development Center (AEDC) is the nation's largest complex of flight simulation test facilities. The center was dedicated in June 1951 by President Harry Truman and named after 5-star General of the Air Force Henry 'Hap' Arnold, visionary leader of the Army Air Forces in World War II and the only airman to hold 5-Star rank. Today, this $7.8 billion complex has some 58 aerospace test facilities located at Arnold Air Force Base, Tenn., and the center's two remote operating locations - the Hypervelocity Tunnel 9 in White Oak, Md., and the National Full-Scale Aerodynamics Complex (NFAC) located on NASA's Ames Research Center at Moffett Field, Calif. The Tunnel 9 test facilities simulate flight from subsonic to hypersonic speeds at altitudes from sea level to space while NFAC provides a critical capability for aeronautics research, particularly rotorcraft research. Virtually every high performance flight system in use by the Department of Defense today and all NASA manned spacecraft have been tested in AEDC's facilities. Today the center is testing the next generation of aircraft and space systems. For more information on AEDC visit the center's Web site at