High costs and long lead times can be a deterrent to innovation. The team at the Landing Gear Test Facility, or LGTF, at Wright-Patterson Air Force Base, Ohio, is trying to lower those barriers for aircraft tire manufacturers.
For roughly a decade, the LGTF team has been cloning runway surfaces by taking casts of runways and then creating concrete tiles used in an internal drum dynamometer for missionized tire wear testing, or MTWT. The team has built up an in-house library of tiles, but still not every runway a customer may be interested in is represented.
Conventional tire testing assesses structural integrity to ensure a tire can handle the loads, speeds, heat and braking experienced during landing and takeoff of an aircraft, but does not account for wear and tear. A tire may be able to survive all the forces, but only do so for one or two landings before needing to be replaced, which is significant in both cost and maintenance time. MTWT conducted by the LGTF team provides a means to assess how a tire wears over time and inform logistical planning and, ultimately, tire design.
In recent years, the LGTF team has been doing 3D runway surface scanning to create digital models of runway surfaces. The goal is to use these digital models to additively manufacture tiles for use in the dynamometer, but until then the data obtained from the models has provided another means to shorten the timeline to test and reduce cost.
The data obtained from the scans allow the LGTF team to truly treat the concrete tiles created through the molding process as a library. A scan of the “cloned” runways provides information such as height differences in the aggregate of the runway and number of aggregate points in a given area. Then, when a customer wants a runway not in the library, the team scans it and looks for a runway that has similar characteristics.
“What we’ve noticed is we can use the scanner and show what is comparable between the surfaces and what is not comparable,” said Sami Labban, LGTF’s Advanced Technology Development lead. “If there is a runway we haven’t cloned yet, we can go out to the field, take a scan of it and look at the data sets to determine what concrete tiles we have in-house that best match it.
“Normally to manufacture concrete tiles is expensive and time consuming, but we’ve used this to show we can use similar surfaces to get an extremely close representative surface and use that for testing, which cuts down a lot on setup cost and time preparing for testing.”
The team, recently, did exactly that for a customer test. The team went and scanned the desired runway and then was able to identify a tile that was 80-90 percent similar. The customer wanted to test at the LGTF as part of an effort to develop an innovative tire design.
To ensure the tile from the library was similar enough, the customer provided their baseline tire to see if the results were comparable to those seen in the field, which they were.
“Then the tire manufacturer gave us two ‘out-of-the-box’ tire design ideas that they didn’t want to go through a full tire qualification to get it onto aircraft to try it out, because that costs millions of dollars,” Labban said. “They said ‘These are ‘out-of-the-box’ ideas that we aren’t sure if they totally work and we kind of want to see if they work.’ It’s a lot cheaper to do here than try to get it qualified and put on aircraft.
“We’re seeing there are a lot of benefits to doing it this way because we we’re able to discover one prototype tire actually did significantly better than the baseline, and the other prototype tire did significantly worse. Then, we’re able to start more quickly doing design iterations and design optimizations prior to going to the field, which saves the manufacturer money on getting a better design more quickly. And, it’s better for the warfighter because you’re getting a better product out to the field in less time as well.”
In order to reduce cost and scheduling time in the instance a specific runway is not well-matched by anything in the tile library, a Small Business Innovation Research effort is underway to additively manufacture the tiles using a runway scan.
“Additive manufacturing cuts time and cost,” Labban said. “We anticipate it will save roughly 20% cost on a test program and save six to eight months of set-up time.”
The team expects to have a full tile produced by the Air Force SBIR contractor, Open Additive, LLC, using additive manufacturing for testing later this year.
Digitally modeling runways will also help efforts to field tires and aircraft faster by contributing to the digital twin, digital engineering efforts.
“The aggregate size, the roughness and the texture affects the friction between the tire and the runway,” Labban said. “Stopping distances of an aircraft would be directly affected by that. These sort of calculations can start to be made and be pieced together to say, ‘Hey, on certain runways we might not be getting the friction coefficients we want in order to land properly.’”
“Gathering this data is really opening up a lot of doors to go and get a lot of detail on some of the physics that are necessary for a lot of these efforts.”