AEDC collaboration with Redstone pays off

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  A collaborative effort initiated by a team at AEDC's Precision Measurement Equipment Lab (PMEL) has resulted in the successful renovation of two major metrology assets for DoD customers of the Army's Primary Standards Laboratory (APSL) at Redstone Arsenal in Huntsville, Ala. 

In 2006, James Winchester and John Adcock, two senior metrology engineers at PMEL, toured the metrology facilities at Oak Ridge, as well as the NASA Marshall Space Flight Center and the APSL, both located in Huntsville. 

"Our goal was to get to know the folks who are working at these labs and see if there was anything that we could do for them or they could do for us," Winchester explained. "We learned that the Army lab at Redstone Arsenal in Huntsville was in a difficult situation with force calibration. Their metrology lab had two older deadweight force calibration machines. The larger machine, capable of producing 102,000 pounds of force, was being operated with severe limitations due to having developed a crack in a weld on the yoke assembly. The Army had built a new facility and purchased two new deadweight force calibration machines, but the manufacturer had defaulted on the last phase of the contract, which was the installation of these machines." 

Winchester said it is important to know how the force calibration machines are used and why a high degree of accuracy is paramount. 

"The U.S. Army will use these machines to calibrate load cells which measure force," he said. "The Army has weighing devices which use the load cells for pre-flight weighing of helicopter and other transport vehicles. We use load cells at AEDC primarily for measuring thrust.

"Thrust measurement at AEDC is a critical parameter for the testing that we do here, both on turbine engines and on rocket motors. These calibrators are utilized to calibrate load cells, which are used to measure force during a test and convert that data to an electronic signal that can be acquired and monitored during testing. One of the most important parameters for jet engines is the thrust produced versus the fuel consumed in the process of converting fuel to mechanical energy. Optimizing the efficiency of this process is an important goal of our engine testing here at AEDC." 

Winchester said the two force calibrators AEDC renovated are only exceeded in accuracy (ability to generate standard force with the lowest uncertainty) in the United States by the force calibrators used by the National Institute of Standards and Technology (NIST). 

"Now, if we need to get one of our larger load cells calibrated with the lowest uncertainty possible outside of NIST, we could possibly work with the Army Primary Standards Lab to get that calibration done" he said. 

Winchester said the work required to get the force calibrators back in operation was labor-intensive and time consuming. The team at AEDC took on the task of renovating the force calibration machines, but first these had to be disassembled and the parts brought back to the center for refurbishing by the Model Shop. 

"This is where the heavy lifting, literally, really began," said Dave Simmons, ATA's Test and Facility Support Branch manager. "Two of our riggers, one of our crane operators and their supervisor were key to the success of the overall effort from start to finish. We brought three truck loads of system components back to the base for the AEDC Model Shop machinists and our painters to refurbish the stainless steel weights and supporting beams. Our folks meticulously took a system that some may have questioned was salvageable after sitting on a hardstand for a while and transformed it into a highly precise system once again. Once refurbished, the riggers and crane operator successfully assembled and installed these components on-site at Redstone." 

Winchester said the project was more complicated than it might have appeared and also involved some fine tuning. 

"We had all the stainless steel weights associated with the large calibrator at our sandblasting and painting facility to be refurbished," he said. "They had to do the cleaning and surface refinishing, and in some cases made mass adjustments, prior to sending the weights to the NIST facility in Gaithersburg, Md., to be calibrated." 

To fully appreciate the scope of the project, Winchester said it is important to understand the physical size of the calibrators. 

"Each of the force machines is comprised of 36 individual mass items calibrated to an uncertainty of less than 20 parts per million by the National Institute of Standards and Technology," he continued. "For the larger machine the calibrated mass will produce a total force of 112,000 pounds in the local gravity at Redstone Arsenal. This large machine stands about 30 feet tall and with support structure and operational hardware weighs approximately 200,000 pounds. The smaller machine will produce 12,000 pounds of calibrated force while standing about 16 feet high and weighing a total of approximately 20,000 pounds. The total weight of these machines together is roughly 110 tons." 

After the weights were calibrated at NIST and all the structural components were refurbished at AEDC, everything was returned to the Army Primary Standards Laboratory. Within weeks of this re-convergence of components, the AEDC Rigger Team returned and began the re-construction and installation effort. 

Vince Chapman, AEDC senior quality assurance evaluator, said the Army had previously received quotes from commercial companies to refurbish these systems. He pointed out that by teaming with AEDC, Redstone was able to avoid much higher costs and save the taxpayers approximately $500,000. 

He also explained that much of the credit for initiating the collaborative effort to get the force calibration machines back in service goes to two people. 

"James Winchester and John Adcock were the ones who had the initial idea to assist the Army," he said. "It was their forward thinking which planted the initial seed and their expertise which helped the collaboration between AEDC and Redstone grow successfully. If it weren't for their keen eyes, the project may have never been realized - what a magnificent contribution both these gentlemen have made." 

The staff at Redstone provided the time schedule, and coordinated with NIST on calibrating the individual deadweights in each calibrator, according to Adcock. Funding for the project and much of the technical coordination for the project was provided by the Army's Product Director for Test, Measurement, and Diagnostic Equipment, headquartered at Redstone Arsenal. In addition, the Army Primary Standards Lab Mass and Force lead engineer, Mark Walczyk, provided technical guidance throughout the refurbishment efforts. 

According to Larry Tarr, the APSL director at Redstone, the new 12,000 pound deadweight force machine has been in full operation for several months, and it has been added to the APSL's Scope of Accreditation to ISO 17025.

"The larger 112,000 pound force machine is still in the checkout and verification phase, and currently is not being used to perform accredited calibrations," he said. "We expect to bring that machine on-line early in 2009."