If Air Force airplanes and helicopters were people, they’d be a large Baby Boomer generation growing older.
The human gray hairs and wrinkles would be fissures, tiny cracks and corrosion.
It is the job of an Air Force Academy lab and its engineers to ensure the Baby Boomer generation of airplanes and helicopters won’t have to retire, that they remain useful for years to come.
The U.S. Air Force Academy’s Center for Aircraft Structured Life Extension (CAStLE) exists not only to provide lab support to cadets learning engineering, but also to research programs focused on sustaining the aircraft for the Air Force.
Among other things, CAStLE tests aircraft parts for fatigue and corrosion of multiple kinds of aging aircraft.
The two largest fleets of Air Force planes are also the two oldest fleets, the C-130s and KC-135s, which were primarily built in the 1950s and 1960s.
“We look at materials degradation,” said Dr. Greg Shoales, professional engineer and director of CAStLE. “In a controlled lab setting, we can perform tests to verify what we think are the impacts of the operations’ environment on that structure.”
The lab tests the aircraft itself and its components, not the electronics of the aircraft.
Materials will degrade over time and under varying environments; an aircraft will corrode or develop fatigue differently in a tropical environment than in a desert environment, Shoales said.
The people managing the aircraft “want to predict what will happen to those structures over time,” he said, “to do inspections and know when it’s time to repair something.”
For example, vehicle manufacturers will recommend changing a certain belt at a certain mileage. Car makers have a general idea when a certain model will likely fail. The same is true of aircraft.
“In aircraft, you want to have some way of knowing when it’s time to repair or replace one part or another,” Shoales said. “You want your structures to continue doing what they’re supposed to do without failing.”
The lab conducts analysis of fatigue crack growth, environmentally assisted cracking, flight data acquisition, corrosion chemistry, structural bonding, bonded repair and composite materials, high-temperature ceramics, failure and metallurgy.
Hefty budget, but …
The lab has a $30 million annual budget but gets no money from the Air Force Academy. Instead, its funders are its customers — the Air Force, Tinker Air Force Base in Oklahoma, Hill Air Force Base in Utah, the Office of the Secretary of Defense, Department of Homeland Security and others.
Regarding funding, Shoales said, “We’re completely outside the Academy. If our funding went away, we’d go away.”
No other department in the Air Force tests aircraft like CAStLE does. The Air Force has a research arm, “but they’re not involved in day-to-day sustainments. They’re long-term,” Shoales said.
CAStLE’s team includes around 20 on-site contract engineers as well as others. The core of CAStLE at the Air Force Academy is four people, including Dr. James Greer Jr., technical director and professional engineer.
The lab works primarily on U.S. Air Force aircraft. It does no work for the National Transportation Safety Board and limited work for commercial airlines, Shoales said.
“There’s the legal umbrellas around those things,” Shoales said.
In one case, the lab researched the impact of fuselage dents on structural safety. A commercial airline heard about the research and “they used the results of that study to streamline their own operations,” he added.
In another analysis, a Sky Crane manufacturer had a repair it needed to certify, so the company hired CAStLE to do the testing for it, Shoales said.
“We have several customers that do send us parts and ask us to determine why it failed,” Shoales said. “If we receive a part that’s been properly preserved, I’d say our success ratio is 100 percent in finding the root cause.
“Our guys are as good as they come regarding determining the cause of any damage.”
Shoales wrote the “best practices” handbook on the tear-down process, which includes the technical direction, planning and execution of the analysis of a complete aircraft.
The team is conducting the most extensive tear-down analysis of four complete aircraft, “nose to tail and tip to tip,” of the KC-135 tanker, Shoales said.
The team began planning the project in 2006 with the goal of analyzing the condition of nearly every square inch of the aircraft. The CAStLE team authored detailed process protocols, which enabled the analysis work to be accomplished at many locations within the United States.
“It is the most comprehensive inspection – first tear-down program in which every part is inspected multiple times by multiple inspection techniques,” Shoales said.