Arnold AFB craftsmen and others join to aid supersonic wind tunnel return to service

ARNOLD AIR FORCE BASE, Tenn. – The reactivation of the 16-foot supersonic wind tunnel at Arnold Air Force Base is on the horizon, and work continues behind the scenes to bring the dormant facility back to life.

Craftsmen in the Arnold AFB Model and Machine Shop are being lauded for the creativity and cohesion that led to the successful completion of a significant undertaking critical to reactivating the facility.

“It was a lot of teamwork,” said Amy Duncan, National Aerospace Solutions project engineer for the Flight Systems Branch at Arnold AFB. “Lots of workers came up with ideas to save money and material. There was a lot of people using their brains and working together.”

Duncan coordinated with the Design group on base to design new tape reel covers that will protect part of the nozzle position measurement system of the resurrected 16-foot supersonic wind tunnel.

The wind tunnel known as 16S, the largest supersonic wind tunnel in the world, has been dormant for more than 20 years. It was listed as inactive in the late 1990s as national priorities shifted and usage of the facility declined.

The reactivation of 16S is set to occur before the end of the year. Paul Wright, Air Force project manager for the return to service project, said the revived facility will fill a crucial need. Due to a reduction in the number of supersonic wind tunnels in the U.S. over the past two decades, 16S will provide test capabilities that cannot be found anywhere else in the nation. Wright said the wind tunnel will play a vital role in the development of hypersonic weapons systems, which is a major focus point of the National Defense Strategy.

“It’s critical for us to get 16S back into operations so we can test these high-speed weapons systems in a developmental test facility before they have to be sent off for flight test so we can find issues with these weapons systems early on in the development process,” Wright said. “This saves the taxpayers a lot of money for the development of these systems and saves the development community significant time and effort in avoiding redesigns. That’s why it’s a critical capability for us as a nation to be able to bring 16S back into service.”

Wright said the 16S return to service project involves two facets. The first is the actual reactivation of the wind tunnel, which is nearing completion. The second is a seven-year, $43 million effort to improve the capabilities of the facility, which is currently in the third year of execution.

Work is underway to replace the 16S nozzle control system, a multimillion dollar project that will significantly increase the reliability of the system and upgrade system functionality.

The tape reel covers are metal boxes that house pairs of encoders used to measure position during 16S testing. The covers shield the encoder gears, bearings and other mechanical equipment within from dirt and dust.

“Trying to keep the dirt and dust out of the gears is a big piece of it for reliability,” said Gary Clower, a NAS planner/scheduler at Arnold AFB. “A couple of grains of sand will lock a gear set up and break a tape. It doesn’t take much.”

Temperatures within 16S can climb to around 600 degrees Fahrenheit during some tunnel operations. The tape reel covers also protect the encased encoders from this intense heat. Contained within each tape reel cover is more than 20 feet of copper tubing through which glycol, used to cool the devices during high-temperature tunnel operations, will be pumped. The completed tape reel covers are also covered in insulation to provide further protection.

Jamie Bobo, NAS designer/drafter, designed the new tape reel covers. His drawings were then used by craftsmen in the Model and Machine Shop to fabricate the boxes.

The new covers serve as a technological update to the tape reel covers that previously lined 16S. Design drawings of the old boxes were found to be of little use but, by taking a closer look at one of the prior covers, Bobo was able to come up with a new design.

“We had an old cover to look at and a set of drawings that nobody could read,” said Chris Broadrick, a NAS planner/scheduler. “Jamie Bobo reverse engineered them and got us drawings and did as-builts.”

Bobo did not merely hand his design off to the sheet metal workers in the Model and Machine Shop. He instead worked closely with them, offering suggestions to help bring the physical manifestation of his design to fruition and listening to the ideas the sheet metal workers proposed to make the fabrication process easier.

“It was a total team effort when it comes to all this,” Bobo said. “I spent a good amount of time at the Model Shop just talking to those guys to figure out how they do it to make my models match the way it was going to be built.”

It was to the sheet metal workers to fabricate a total of 116 complete tape reel covers. They did this by making 232 halves that were then assembled to form complete units. After building a few prototypes, the sheet metal crew went to work.

“We never really knew how long it would take to make one because we started out with mass production,” said Dominic Marzicola, a NAS sheet metal worker.

One half of each complete tape reel cover required a 2 inch-by-2 inch protrusion to provide room for the encoder. Bobo said the designers worked directly with the sheet metal workers to change the original plans for how this projection would be accomplished.

“They came up with ideas for the actual encoder box,” Bobo said. “We were originally putting it on the outside. We instead put it on the inside to make it a whole lot easier for them to be able to fabricate.”

The sheet metal workers sought further help with the small encoder protrusions from others in the Model Shop. They approached machinists, who built a punch which allowed for the easier creation of the protuberances.

“This was really a big challenge for us because most of the time we just make two or three items of one particular kind, but this was kind of a mass production,” said Paul Gallagher, a NAS sheet metal worker. “Luckily, we had the resources available to punch all the holes out and bend the metal and do everything that we had to. It was a real good effort among all of us.”

Each complete cover also required a port to allow for connection to an electric power source. To speed up the process, sheet metal worker Andy Riis, with the help of machinist John Adams, developed a welding device they referred to as a “purge plate.” Argon gas is pumped through the small, crescent-shaped device which is used to form half of the port on each cover half.

The copper tubing was bent into a trapezoidal shape to fit within each of the 116 covers.

Before this work began, NAS Planner/Scheduler Riley Hoge used a small piece of wire to “route” the path tubing the way it should be bent. This information, along with a 3D model completed by Bobo to show what the completed tubing would look like, was provided to Model Shop programmers. The programmers then modeled a flat version of a jig that could be used to provide greater ease and consistency in the bending of the copper.

This jig model was passed on to Model Shop machinists who used the model to fabricate a physical jig from a sheet of metal. This jig included grooves that represented the route the tubing was to take, holes for placement of bumpers around which the tubing was bent, and lines to indicate where the tubing needed to be folded.

The jig was utilized by Model Shop pipefitters responsible for bending the tubing into the correct size and shape.

“We brought it down here and started working it, and these guys, throughout the process, came up with multiple different ideas of ways to improve it and make it more efficient,” Hoge said.

These suggestions included placing the flat jig on a turntable, which allowed pipefitters to spin the jig when a bend was required on the opposite end rather than walking around the workbench to reach it.

Hoge said the tubing jig, along with Riis’ welding device, provided considerable cost savings.

The completed tubing was clasped into the covers by Model Shop sheet metal workers as they fabricated the boxes.

“I pretty much think the guys in the Model Shop perfected the way they needed to do that,” Clower said. “There were at least a half-dozen times that there were ideas brought out of the sheet metal shop that I’m aware of, plus ones I’m not aware of, I’m sure. There was a lot of improvements that were made that came from the hands-on guys making it.”

Like the jig and the metal bumpers used to bend the copper, the clips used in the tape reel covers were fabricated in-house. Marzicola said the sheet metal workers made more than 5,500 small metal clips for the project.

Wright said the tape reel covers will not only provide increased reliability immediately, they will also help enable the running of live engines in 16S in the future.

“So it’s doing two things – it’s increasing reliability and it’s preparing us for future capability increases,” he said.

Wright added he is grateful for the contributions of the craftsmen in the return to service project.

“I’m very appreciative of all the efforts that have gone into this, not just from the standpoint of the time and the hours and the labor that went into it, but also seeing how a team can work together,” he said. “I know sometimes it can be difficult when you’re working with multidisciplinary organizations to get folks to understand how to integrate to get a job done.”

The fabrication of the new tape reel covers began in July and was completed in mid-December, ahead of the Dec. 20 deadline.

Duncan said money was saved on the project by utilizing the resources available at Arnold and relying upon the expertise of craftsmen in the Model Shop rather than outsourcing the fabrication of the covers.

“They were close by. They had the same mission that I have,” Duncan said of the craftsmen. “We all are working for the same purpose.”

Engineers, project managers, designers and others involved were able to build stronger relationships with those in Model Shop throughout the course of the project – connections that could prove beneficial in future projects.

“AEDC is a wonderful place because it has all these tools, all the knowledge and the people that can do all these different jobs,” Bobo said.

Hoge said there was some trial and error for the Model Shop craftsmen early on in the project, but they were able to overcome any obstacles they faced with steady communication amongst each other and others involved. He said the ingenuity on display throughout the process can be observed across Arnold.

“That’s what makes this base go,” he said. “You’ve got people who care enough to try.”

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