AEDC workers meeting challenge of returning wind tunnel to service

  • Published
  • By Patrick Ary
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  A look at the photos shows the scope of the damage: two-inch thick steel plates cracked and peeled away from stabilizers as easily as peeling the shell off of a boiled egg.

The daunting task of repairing the damage in the Von Kármán Gas Dynamics Facility (VKF) Wind Tunnel A is kind of like putting Humpty Dumpty back together again, except Humpty Dumpty is made of tons of steel and complex motor and monitoring systems.

Also, unlike the "king's men," AEDC workers fully plan to put the nearly 60-year-old facility back together again.

Wind Tunnel A has a computer-controlled nozzle that is designed to simulate flight speeds up to Mach 5.5, but the air has been still for the last couple of months due to an equipment failure that resulted in some seriously mangled pieces of metal.

The cause of the damage was an actuator that failed, allowing the diffuser plates to collapse into the tunnel, according to AEDC Ground Safety Manager Mike Norris.

During preparation for a test, the falling actuator and a resulting change in pressure pushed diffuser plates past their intended points of articulation, bending the plates and breaking the pins holding them in place.

"This thing collapsed and there was a lot of stuff that went down to the (foreign object damage) screen on the other side," Norris said.

Now crews are busy getting all aspects of the facility back online, from fixing diffuser plates and damaged screens to preparations to add all the measurement systems back in.

The failure happened as the tunnel was being prepared for a Standard Missile test project managed by Air Force 2nd Lt. CharMeeka Scroggins. She said because of the failure, the customer just completed a test in 16T and will be testing in Tunnel B next. Those tests were supposed to be done after Tunnel A testing, but Scroggins said everyone had to get together and reschedule to get the job done.

"We were prepped for the Tunnel A test at that particular time and then we kind of had to shift gears," Lt. Scroggins said. "But the project team did a really good job on both sides of the house - on the government and the ATA side - in working together to accomplish our re-planning."

But re-planning doesn't mean the need to have the tunnel back up and running has gone away.

"They still need Tunnel A," said Tom Miller, VKF test asset manager and member of the team working on returning the tunnel to service. "And they're anxiously waiting for us to get back operational."

Getting operational meant some serious work for the Model Shop that is ongoing. It all started with determining the extent of the damage and coming up with a repair plan.

ATA test and support facility manager Walt Bishop said it has truly been a team effort between ATA and the Air Force and credited the Return to Service team with putting together and managing an aggressive yet realistic plan to have the tunnel operational in a short period of time.

"John Hopf, Lisa Waddell, Steve Simpson, Kim Sudberry, Jeff Tate and Jeff Harvey - to name a few - assembled a workable plan in a short period of time to fix a very complex problem with many unknowns," Bishop said.

The repair of the plates is being worked in the Model Shop, where boilermakers are bending and welding large plates of steel in preparation for the machinists to finish machining the plates to tight tolerances.

"This particular repair highlights one of the greatest benefits of working with the Model Shop ... that of concurrent engineering," Bishop said. "Jim Childers and Jeff Earls, design engineering, are working closely with our skilled craftsmen on a daily basis tweaking and monitoring the repairs as they progress.

"I hate to use the term quick fix. It wasn't quick at all," Bishop said. "But it was quicker than the complete refabrication of the plates."

Still, some portions of the damaged plates had to be cut off and rebuilt from scratch. The welding work varied from welding in extremely tight spots to welds that were two inches wide.

An added complication to the work was the fact that the type of steel the plates were made from in 1952 isn't readily available anymore. Steve Ary from the Metallurgical Lab worked with Model Shop boilermakers to develop a weld procedure to allow them to weld three different metals.

"The boilermakers did a fabulous job, which is allowing us to continue on," Bishop said. "Now we're rolling over to the machining phase, where our machinists will finish the plates."

The machining work has to be precise, Bishop said, because the plates include a sealing surface that is critical. Alignment has to be exact.

"I am very proud of the return-to-service team and the skills and abilities of the Model Shop," he said. "This work was unscheduled, so we had to insert a large job into an already tight Model Shop schedule. But using flexible scheduling and surge capacity, we have been able to work this effort and still maintain our customer's needs and those elsewhere on base."

The return to service has meant more than just getting diffuser plates back in order. At least three control systems in Tunnel A had to be removed before the plates could even be taken out.

ATA Technical Specialist Kim Sudberry said the majority of the Tunnel A Diffuser Control System (TA DCS) - consisting of the actuator motors, conduit and associated control wiring for the actuators - had to be removed. Other control systems that required disassembly were the Tunnel A Diffuser Position Measurement System - which is used to determine diffuser area - and the system that measures the thermal expansion of the plates, which is known as the Tunnel A Diffuser Sidewall Protection System.

"[Those are] the first things to come out, because that stuff's in the way," Sudberry said. "Not only is it the first thing that has to be taken out, it's the last thing that has to be done when you're ready to operate again."

The damage that occurred in Tunnel A happened at a time when there were plans already in place to upgrade some of the equipment there. Parts have been ordered and are on the way for work that is scheduled to begin sometime in May.

Sudberry says he is taking the "work smart, not hard" approach to the repair work because of the upcoming upgrade project.

"Some of the original instrumentation design will be incorporated in the new design," Sudberry said. "And I've worked with the design team to use what I call smart engineering practices relative for the return to service, (saying) 'Hey if you're planning on replacing this with new materials, let's find a common junction. There's no need in doing the work twice. So let me have it and as part of the return to service, I'll put it in.'"

The current target date to have Tunnel A back in service is mid-April. Miller believes it will be ready.

"Once the (return-to-service) team was assembled, we had the right skills and the right players to get the work done in the time frame we need to get it done in," Miller said.