An innovative effort at the Landing Gear Test Facility at Wright-Patterson Air Force Base, Ohio, aims to improve the way the Air Force evaluates the impact of runway friction on aircraft tire wear.
Air Force Materiel Command allocated more than $4.6 million in Squadron Innovation Funds in fiscal year 2018, with $23,000 augmenting the 3D Runway Surface Scanning and Surface Re-Creation at the LGTF.
This effort has been in the works for many years, explained Scott Wacker, 704th Test Group Aerospace Survivability and Safety Office flight chief.
“The 704 TG Aerospace Survivability and Safety Office at Wright-Patterson (AFB) has spent over a decade at the Landing Gear Test Facility developing advanced test methods that allow the evaluation of aircraft tire and runway friction interaction and tire wear,” Wacker said.
“This effort has focused on developing innovative technologies and processes to more accurately simulate real-world tire performance in the test facility. At the heart of this work is the 168-inch internal drum dynamometer, which is a world-unique test machine developed and commissioned in 1998 for the purpose of aircraft tire wear testing.”
The 168-inch internal drum dynamometer, or 168i, operates at speeds up to 350 mph, with loads of up to 150,000 pounds, plus or minus 20 degrees of yaw, plus or minus 10 degrees of camber and can provide variable levels of brake torque.
“All of these aspects can be dynamically programmed to replicate aircraft ground operations,” said Jonathan Childress, the test manager overseeing the 3D Runway Surface Scanning and Surface Re-Creation project. “Also, the tire footprint pressure on the internal drum dynamometer more closely resembles tire footprint pressure on a flat surface than it does on an external dynamometer.”
In the early years of the 168i, tire testing was limited to comparative wear testing. This was accomplished by lining the interior of the 168i drum with grit paper and performing various rolling tests. Tire-wear testing on the grit paper was unrepresentative of the wear experienced in the field and was incapable of providing data on ground handling characteristics.
The 704 TG/OL-AC LGTF team has since developed the capability to clone Air Force concrete runways and line the interior of the 168i with the replicated runway surface. Although the process is time-consuming and costly, runway surface replication is an instrumental capability that makes possible ground handling evaluation and tire-life predictive testing, known as Missionized Wear Testing.
The development of these new test capabilities has provided the Air Force and Department of Defense with a method to evaluate aircraft tire performance prior to mass producing and fielding tires, which translates to improved safety-of-flight and greatly reduced acquisition and logistics costs.
“Until recently, little thought was given to the runway surface’s influence on aircraft tire wear and ground handling characteristics. It was understood that replicating the runway surface on the 168i was critical for accurate testing. However, the extent of the influence the surface characteristics had was not well known," Childress said.
“While working with the Navy on an aircraft ground handling test program, the 704 TG/OL-AC was made aware of a Navy Program to develop a 3D laser scanning device for use on aircraft carrier deck surfaces.
“After discussing the capabilities of the carrier deck scanner with a Navy support contractor, a demonstration was arranged during one of the team’s field investigations to an Air Force runway. The prototype showed promising results when testing on a concrete runway and it was clear that a little innovation could provide a very useful tool for the U.S. Air Force,” he said.
With some modification, it’s anticipated that the specialized laser scanning technology will provide a consistent method for acquiring high fidelity 3D topology maps of concrete runway surfaces. Customized post-processing software algorithms will generate parameters for important characteristics of the runway surface texture that relate to tire ground handling performance and tire wear.
According to Childress, the 704 TG/OL-AC plans to couple these parameters with tire testing performed on replicated runway surfaces in its 168i, and correlate these surface properties to friction properties and tire wear.
“In time, a digital library of every (Air Force) runway could be acquired and analyzed to offer important insight into aircraft ground operations and tire life,” he said. “The Air Force Civil Engineering Center has expressed interest in this technology as well and could potentially use the information gained from this technology to drive decisions about runway design, maintenance and repair.”
The 704 TG/OL-AC is also leading a Phase I Small Business Innovation Research program to develop the capability for additive manufacturing of replicated landing surfaces for the 168i.
“If this technology is successful, the scans acquired from the 3D white light runway scanner could be directly used as inputs for the AM (additive manufacturing) process,” Childress said. “Using a digital library of Air Force runway surfaces, test surfaces for the 168i could be created in-house leading to reduced lead time, cheaper procurement and greater control of quality.”