Over 60 years, AEDC wind tunnels have seen a wide variety of work Published June 10, 2011 By Patrick Ary AEDC/PA ARNOLD AIR FORCE BASE, Tenn. -- When the Air Force sent Capt. Win Phipps to AEDC in 1989, his last job before being assigned to the base was to switch phones over to a new digital system. Today, as a civilian test manager for the base's wind tunnel systems, he has seen advances in aviation that go way beyond the jump from an analog to a digital phone. "In the 90s I supported numerous strategic planning sessions at the Gossick Leadership Center for years, and I remember all the debates on whether we'd see unmanned fighters or unmanned aircraft," Phipps said. "That debate went on for several years, and now remotely-piloted aircraft has become the norm for aircraft in development that we may see." In fact, today the premier unmanned aircraft - the RQ-4 Global Hawk used extensively in the wars in Iraq and Afghanistan - was tested in AEDC's wind tunnels during its development. It's one of several leaps forward in aviation that was put to the test at Arnold AFB. AEDC operates wind tunnels in two primary facilities on base: the Propulsion Wind Tunnel Facility (PWT) and the von Kármán Gas Dynamics Facility (VKF). AEDC also manages two wind tunnels at remote operating locations: the Hypervelocity Wind Tunnel 9 in Maryland and the National Full-Scale Aerodynamics Complex at Moffett Field, Calif. The body of work that has come through the tunnels in the last 60 years is staggering. The facilities are capable of aerodynamic and propulsion integration testing for large-scale aircraft models. Propulsion systems and inlets can be tested simultaneously in PWT to make sure engines receive adequate airflow. Workers can also test store separation systems to ensure bombs and missiles separate cleanly from aircraft when released. Because of the vast capabilities of the tunnels, they've seen everything from fighter jets to weapons systems and space vehicles. There have even been tests on parachute systems and ejection seats, according to ATA Aerodynamics and Propulsion Section Manager Bill Peters. "We have actually performed ejection seat testing with instrumented mannequins exposed to the actual flight conditions and orientations," Peters said. "Testing has been conducted to simulate the environment that might be expected as the pilot was ejected from the cockpit. Often times, the tests in the past were to measure loads on the head, torso and limbs and occasionally we might see a loss of an arm or a leg. We've done a large variety of testing to ensure the flight safety of both aircraft and missiles and occasionally their occupants." AEDC currently does much of the pre-flight safety certification process for weapon separation testing of missiles and stores from parent aircraft as part of what is called the Capture Trajectory System (CTS) integration testing process. Prior to the advent of computers at AEDC in the 60s, much reliance was placed upon slide rules and tables of typical aerodynamic properties as part of the trade in preparing for tests, Peters said. Because computational fluid dynamics (CFD) didn't exist at the time, experimentation was fraught with risk but the intent was to use ground test facilities over flight testing to gain a first level of understanding of risks and to reduce them prior to full-scale development. Likewise, in development of the current test facilities at AEDC, smaller-scale model wind tunnels were built to assist in the design of the current larger facilities like 16T and 16S. Tunnels 1T and 1S were constructed and helped pave the way for the base's 16-foot-square tunnels. Likewise, Tunnels D and E were forerunners to VKF Tunnels A, B and C. "We did not have CFD tools, so what could be done but to rely upon the work and theories of aerodynamicists such as [Dr. Bernhard] Goethert and [Dr. Theodore] von Kármán and their insights on the important features for the design of the facilities?" Peters said. "Pilot wind tunnels at AEDC were used to discern and discover the essential geometry and performance features for design. With the modern resources of desktop computing and processing, computational tools are continuing to be developed, which add a significant ingredient in risk reductions of testing in the wind tunnels." The first PWT test was performed in June 1953 on a .03-scale model of the Bomarc missile for the Boeing company. It was conducted in a one-foot cross-section prototype transonic tunnel know as "PeeWee." That tunnel was the predecessor for the 16-foot transonic tunnel 16T, which was completed in 1956. That facility is still in use today - a fact that ATA Flight Systems Product Manager Rick Bishop says is a testament to the engineers of that time. "All of the rotary drive equipment is pretty much what came with it," Bishop said. "Improvements have been made over the years, but it's all pretty much the original design philosophy the whole way through." 16T can operate at transonic Mach numbers from .05 to 1.6. Its size allows for full-scale missile installations to test engine performance and airframe aerodynamics, as well as the capability to test parachutes or other decelerators. Its supersonic sister tunnel, 16S, is currently inactive. PWT's four-foot aerodynamic wind tunnel, 4T, is capable of testing from subsonic to low-end supersonic airspeeds and excels in store-separation testing. VKF contains three smaller wind tunnels: Tunnels A, B and C. They are used extensively to develop supersonic and hypersonic flight vehicles. Virtually every high-speed flight vehicle has required testing in VKF's facilities. Re-entry vehicles, space capsules, winged vehicles and X-series planes have all gone through testing there. Tunnel A is capable of simulating Mach numbers ranging from 1.5 to 5.5 by use of a continuously variable nozzle that uses steel plates, similar to those in PWT's tunnels. Tunnels B and C are hypersonic tunnels that can generate velocities of Mach 4, 6, 8 and 10 through the use of fixed conical-shaped nozzles. Tunnel C offers aerothermal testing up to 1,440 degrees Fahrenheit for test articles like space vehicles. "In VKF we've done just about as much work for NASA as anything," Peters said. "The space shuttle and a lot of the concepts that led up to the shuttle were tested there, and even some follow-up things that we're talking about ... the Orion and Ares tests, most recently." And while there are other facilities around the country, Phipps said AEDC's stand out in terms of the amount of data that can be gathered during a test. "For our supersonic and hypersonic tunnels, there's really no near peer in production," he said. "There are other blowdown facilities that operate in those ranges and smaller test sections for those supersonic and hypersonic tunnels, but there's no peer in terms of both size and production." In 1993, AEDC became involved with Pressure Sensitive Paint (PSP) technology. The technique uses a special paint and illumination source combined with a sensitive camera to obtain surface pressure data. The light source excites the layer of paint, which fluoresces with intensity inversely proportional to the surface pressure on the model. A system installed in 16T in 1999 uses the PSP data to determine surface pressure at several hundred thousand points on a model, as opposed to conventional instrumentation that is limited to several hundred pressure measurements. A military pilot's career in the air can touch a wide variety of systems that were tested at AEDC - from the T-38 Talon used as a trainer for fighter pilots to the F-35 Joint Strike Fighter Lightning II currently being tested in the field. "We test for the Air Force, Navy and Army, and we do some work for commercial customers," Bishop said. "Most of our testing in the last couple of years has been Air Force and Navy, including extensive testing for the F-18 program. We've supported several other smaller programs during this time, including test programs for the F-15 and various missiles for the Missile Defense Agency." F-35 development was completed after more than 10,000 hours of wind tunnel testing at AEDC, including aerodynamic and propulsion tests. Today, the center is still doing F-35 work in relation to store separation testing. The next big project at AEDC will likely be a next-generation bomber for the Air Force. "That's something that is at the top of Secretary Gates wish list, and he wants to field the capability into the mid-2020s," Bishop said. "We're expecting in the next year or so to start getting inquiries for ground testing to support that new bomber program, so that will be potentially the next large program we'll be involved in." Phipps is also looking forward to the future of testing next-generation fighters and cruise missiles. Thinking back to the unmanned aircraft debates he used to hear on base, he said he thinks hypersonic vehicles may be on the same track - closer to a reality than anyone really suspects. The work environment that a possible next-generation bomber or other future project would be brought into has changed over the last six decades. Although PWT and VKF do similar work, when both Bishop and Peters arrived the two facilities were managed independent of each other. "Essentially, it was almost like different companies operating different facilities," Bishop said. "It was really one company, but there was a different management structure in each facility. Each one independently had their own set of test operations and facility and projects engineers. So while doing similar work, they developed a different philosophy and a different methodology for doing it." Bishop said that has changed as budgets and the nature of work being done has changed. "We're not doing as much facility research," Bishop said. "We're more into test data production than we are into development of the facilities, so we're trying now to blend PWT and VKF test methodologies into a single production model for all wind tunnels." There are several modernization projects either underway or on the near horizon for the PWT and VKF wind tunnels. They include putting in a new mechanism to allow for a larger pitch and roll capability for test articles in 4T, new actuators for the variable nozzles in 4T and Tunnel A, a new common data system, consolidating the control rooms for Tunnels A, B and C into one operations center, rewound drive motors, new starting systems and digital plant controls in the VKF main plant - bringing together some of the facilities developed in the days when multiple contractors such as Sverdrup, Calspan and Micro Craft Technology were working on base. "We had Sverdrup and Calspan that operated these two areas, so PWT and VKF had similar functions but facilities and operations were quite different in look and feel," Phipps said. "But we have this modernization effort and everything's coming together. We're all one big team now, the look and feel of the transonic and hypersonic test business is becoming what we always wanted. I think that standardization of our test processes is going to be a great thing." Today, the people who work at AEDC have that knowledge and, combined with the facilities on base, their decades of experience are what make the work that goes on here a success. "It's maybe a little unusual in that many people have spent entire careers at this one location and have developed intimate knowledge of these facilities over those years," Bishop said. "And when those people leave you can feel the loss, because you have to go pick up with new personnel and re-plow all that ground and re-learn the protocols and test techniques critical to our business. People are the most important part of keeping the operation going." When asked why people have remained at AEDC so long, Bishop said for him it's the reward of knowing he contributes to the defense of the nation. "America is the greatest nation, government and people that has ever existed," he said. "And I want to see that preserved for future generations. I would like to see a lot of these concepts - how we were founded and how we're governed - spread to other parts of the world and eventually get rid of the conflicts and differences that keep us apart. Preserving this manner of life is an important part of what we do here." Peters aspired to be an astronaut when he was younger and also considered becoming a pilot in the Air Force. Instead, he chose a career that he said couldn't have been more rewarding from a technical standpoint. And with a son-in-law who is a Navy aviator, he says there's a sense of satisfaction in knowing that the work he does at Arnold is helping keep his son-in-law safe when he has to go overseas. "We're not in the Armed Forces," Peters said. "We don't wear a uniform to protect our country. But in a way, we protect our country by providing the information that is needed to give the Armed Forces the tools they need to continue preserving freedom."