Tyndall Air Force Base --
In an era of diminishing resources and increased operational deployments, military officials are driven to find fast, cost-effective solutions to problems that previously would have been solved through years of study, refinement and practical trials. Today’s reality requires that engineers, scientists and program managers deliver products to the field in a much more expeditious manner.
Engineers from the Air Force Civil Engineer Center (AFCEC) and the U.S. Army Corps of Engineers’ Engineer Research and Development Center (ERDC) recently combined efforts to answer a question airfield managers, specifically those that are deployed for emergency or contingency operations, have been asking for years – “When do I need to perform Rubber Removal?”
One area where technology has provided a tremendous capability leap is in cell phone applications, or apps. According to a study by Forrester Research, mobile devices are popular today, and their popularity won't wane in the next 10 years, even as newer technologies appear on the scene.
Andrew Ward, ERDC research physicist, Airfields and Pavement Branch, and Dr. Craig Rutland, AFCEC pavement engineer, teamed up to develop ERDC DECEL, an app that could be used to measure friction on runways.
“Airfield managers have expressed the need for a friction assessment tool that is cost effective and easy to operate for quite some time,” said Rutland. “Currently, if an airfield manager or a pavement inspection team needs to measure friction, they need an expensive specialized device that will continuously measure friction at a high speed. The problem is, those are not always available. Plus, those devices and the labor it takes to run them are cost prohibitive in deployed environments. What we wanted to do was harvest the technology inherent in every smartphone through the use of its internal accelerometer.”
According to a paper published by Ward and Rutland, prior to the advent of continuous friction measuring equipment, accelerometers were the go-to tool for conducting friction assessments. In layman’s terms, friction surveys give the airfield manager an idea of an airfield’s skid and rolling distance. They can also be used to measure an airfield’s relative safety in cases of surface contamination – things on the runway like oil, snow or rubber – all of which can cause hydroplaning during wet conditions. Initial results indicate some phones with the app not only have the ability to reliably and repeatedly measure the relative friction as rubber builds up but also correlate well with the continuous friction measuring equipment.
“There are a number of devices that are used to conduct friction surveys both by military and civilian airfield managers,” said Ward. “One of the more common is a device known as a continuous friction measuring device. This device is towed behind a moving vehicle. There’s also a walk-behind model but the real issue is they all require having the equipment available and trained technicians on hand.”
Ward and Rutland say the primary objective of the work leading up to app development was evaluating the use of smartphones as deceleration-based friction assessment tools. They then developed Android and iOS based apps using the phones’ accelerometer (acceleration) and magnetometer (rotation).
“We did extensive testing and validation on a variety of phones,” said Ward. “We wanted to make sure the phones delivered consistent results no matter the platform. They needed to work on both Android and Apple devices.”
The study began in September 2016 and app building started in November of the same year. As the app development progressed, some surprises emerged. Micro-machined, more commonly referred to as MEMS, accelerometers operated under the same principles as full-size mechanical and solid state accelerometers; however, due to their small size, they proved to be more susceptible to fringe effects that, according to experts, can be safely ignored in full-scale devices.
“The most troubling of these effects, I've found, was a temperature dependence on the bias of the accelerometer output signal,” said Ward. “This brings into question not only which accelerometer is in each device, but also where the accelerometer is in the device with respect to heat sources (batteries, screen backlights, etc.). “
Ward says that at this time, the fluctuations in accelerometer output due to temperature changes are not being adjusted for, and that the temperature dependence of the phones is but one factor being used to determine device suitability for pavement friction assessment.
“We are well on the way to fielding the ERDC DECEL,” said Rutland. “However, we will continue improving and refining the product, even after it is fielded. Products like these evolve with the technology, also as the app is used in the field we will incorporate the feedback of the Warfighters - the people who will be using the app. We’re also getting input from the Air Force Flight Standards Agency.
“Everything we do here at AFCEC is focused on delivering solutions to the Warfighter. It is our job to make sure those fighting to keep this country free have what they need,” Rutland added. “We do that by harvesting cutting-edge technology and mixing it with science and engineering to deliver state-of-the-art products.”
Officials expect the ERDC DECEL app to soon be available at no cost to those supporting military operations.