Engineering foresight: ERDC’s vibration study keeps B-2 hangars mission ready

OMAHA, NE by Tim Reeves (ERDC) — For nearly four decades, the B-2 Spirit, commonly referred to as the stealth bomber, has been the tip of the spear in the United States’ ability to project force on a global scale.

The aircraft’s capabilities – developed in secret and once thought impossible – were on full display during the recent Operation Midnight Hammer, in which the aircraft was used to dismantle assets with Iran’s nuclear weapons program.

During the earliest days of the B-2 program, before the aircraft would be stationed at Whiteman Air Force Base in Missouri, an engineer from the U.S. Army Engineer Research and Development Center (ERDC) provided expertise to help with the design of the B-2 hangars.

The U.S. Army Corps of Engineers Omaha District was charged with constructing the future Aircraft Maintenance Docks (AMDs) for the bomber. While these docks were being designed and constructed using existing materials and techniques, this aircraft had unique operational requirements.

Other aircraft are towed out of their hangars before running their engines outside. Because the B-2 must take-off immediately to protect itself with its stealth features, the standard operation is for it to taxi out of its hangar under almost full power to “jump the curb” of its hangar door.

For this reason, the hangars would be subject to significant acoustic noise each time the aircrafts exited.

James Wilcoski, a research structural engineer at the ERDC Construction Engineering Research Laboratory and a vibration expert, was contacted by the Omaha District to review construction plans, materials and aircraft operational plans to see if the hangar could withstand the vibrations generated by the engines over the aircraft’s life.

“Omaha District became concerned about vibration issues in the hangar because the aircraft had to be able to taxi out under its own power,” Wilcoski said. “That introduced a whole number of different concerns about things falling and getting ingested into an engine.

“The engine manufacturer provided acoustic levels with respect to frequency at various distances from and orientations relative to the engines.”

The study was conducted in 1989 and 1990 and was co-authored by Wilcoski and Lou Southerland, an expert in acoustics who had a more than a six-decade career in the fields of acoustics and vibrations.

Their final report defined estimates of the vibration response of various structural and non-structural components and provided recommendations for construction materials and techniques. Among their suggestions were encapsulating fasteners, increasing ductwork thickness and improving connections. The report also detailed vibration isolation guidance for pipe systems, light fixtures and more. 

“We couldn’t have anything eventually shake loose, shake down and fall into an engine,” Wilcoski said. “You can’t have that. The overall structure wasn’t at risk of collapsing, but it was more of the concern that severe vibrations over the years could eventually cause things to rattle loose.”

In the end, Wilcoski said the district incorporated each of the report’s recommendations.

Later, during a visit to Whiteman when the first B-2 arrived, Wilcoski and Sutherland saw the aircraft for the first time in-person inside the first hangar.

The aircraft was anchored to the hangar floor and the engines were run at 90 percent power, while the two measured acoustic levels and monitored the response of the building and non-structural components, observing the effectiveness of their recommendations.   

“It was impressive; a large aircraft,” he said. “People have called it a flying wing and, you know, that’s what it looks like.”

Even as the B-2 Spirit approaches the end of its service and the B-21 Raider is set to take its place in the coming years, the analytical research Wilcoski and Sutherland conducted nearly 40 years ago remains important to the Omaha District and the U.S. Air Force.

“In 2020 I received an email from Omaha about the maintenance docks they’re building for the B-21,” Wilcoski said. “It was good to know the recommendations we made for the B-2 are being incorporated into the new docks as well.”