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Innovation advances test operations at Arnold AFB hypersonic propulsion facility

Electricians Lon Britt, left, and Robert Campbell, right, along with electrical engineer Adam Webb look at a rectifier, like one that was responsible for an un-commanded "runaway" condition, outside the AEDC Aerodynamic and Propulsion Test Unit at Arnold Air Force base. Webb improved the logic used in the Programmable Logic Controllers on the units to handle un-commanded "runaways,” which allowed him to identify the part at fault. (U.S. Air Force photo by Jill Pickett) (This image has been altered by obscuring items for security reasons.)

Lon Britt, left, and Robert Campbell, right, electricians, along with Adam Webb, an electrical engineer, look at a rectifier outside the Arnold Engineering Development Complex Aerodynamic and Propulsion Test Unit at Arnold Air Force Base, Tenn. Webb improved the logic used in the Programmable Logic Controllers on the units to handle uncommanded "runaways,” which allowed him to identify the part at fault. (U.S. Air Force photo by Jill Pickett) (This image has been altered by obscuring items for security reasons.)


Improvements by team members from the Arnold Engineering Development Complex Aerodynamics and Propulsion Test Unit at Arnold Air Force Base have prevented unscheduled downtime and avoided equipment damage at the facility.

Adam Webb, an electrical engineer for the test operations and sustainment contractor National Aerospace Solutions, improved upon software for the rectifiers by enabling it to detect an unsafe condition and restore the rectifier to normal operations, preventing damage to expensive equipment. A rectifier is an electrical device that converts alternating current to direct current.

The software was successful during a recent APTU test, when one of the rectifiers went into an uncommanded runaway.

“A runaway is when the output current increases significantly above the set point value,” Webb said. “If left unchecked, it can cause the APTU Facility Control System to trip the heated fuel system offline. This results in an unplanned early test termination, possible damage to the heated fuel system and a required repeat of the test conditions. A repeat test at APTU can be expensive and could cause additional degradation to the test article.”

Webb explained that the software modifications also allowed him to isolate the cause of the uncommanded runaway.

“When the software detected a runaway, it swapped control modes,” he said. “This enabled us to continue normal operations and provided the run data we needed to better understand what was really going on. With this new information we were able to determine that a poorly-designed component connection by the manufacturer, along with high vibration during testing, was causing the issue. We developed a new connection method which eliminates the potential for this to occur in the future.”

Sharon Rigney, APTU group manager for test operations and sustainment at Arnold AFB, commended Webb for his work improving upon the rectifier software.

“Innovative ideas and forward thinking in anticipation of possible failure modes and problems greatly improves the performance of our instrumentation, data and controls systems,” she said. “Adam is to be commended for his proactive approach towards possible failure modes and correction actions.”

Efforts by Gareth Penfold, an instrumentation data and controls engineer, have also benefited APTU. Penfold moved to fill an immediate need in APTU for improved tracking of the test, measurement and diagnostic equipment due for calibration.

“Gareth leveraged a previous spreadsheet method of tracking instruments into a fully-functional computer database format,” Rigney said.

This database format allows instrument technicians, instrumentation data and controls engineers and other APTU team members to know what equipment is due for calibration at any given time, and it includes an inventory of spare instruments available substitutions of failed items or items needing calibration. Additionally, the new database keeps track of warranty dates and time-sensitive information required for engineering decision making.

“We were previously working off a giant spreadsheet that was hard to interpret and update,” Penfold said. “To make the process easier, I turned it into a Microsoft Access database system that allows us to look ahead and pull up reports on testing and maintenance. Now, we can know when it is best to calibrate so that we can meet the Air Force requirements for calibrations.”

He added that previously it was hard to determine where different instruments were located.

“We can now see where those instruments are, and we’re also more prepared if an issue comes up, which helps to prevent lost test time,” he said.

Penfold has only been working at Arnold AFB for two years, but management is already taking notice of his hard work.

“Gareth’s ingenuity and attentiveness has produced a tool that will reduce the need for emergency calibrations or waivers, which recently has been a focus area for the Air Force,” Rigney said.

NAS management has recognized both Penfold and Webb with Significant Contributor Awards for their efforts.

APTU is a blowdown wind tunnel designed for aerodynamic testing of supersonic and hypersonic systems and hardware at true flight conditions. Given its versatile design, APTU can support a myriad of test setups: propulsion, material, structures, store separation and directed energy lethality. The facility can produce test conditions from Mach 3.1 to Mach 7.2.

Most recently at APTU, Air Force Research Laboratory and Air Force Test Center ground test teams set a record for the highest thrust produced by an air-breathing hypersonic engine in Air Force history.


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