EDWARDS AFB – With approximately 1,500 potentially active volcanoes worldwide, more than 80 commercial aircraft have unexpectedly encountered volcanic ash in flight and at airports in the past 15 years, according to the United States Geological Survey. Seven of these encounters caused in-flight loss of jet engine power, which nearly resulted in the crash of the airplane.
To further investigate the cause behind these incidents, NASA has partnered with the 412th Test Wing, Air Force Research Laboratory, Federal Aviation Administration, Boeing Research & Technology, Pratt and Whitney, General Electric Aviation and Rolls-Royce Liberty Works, to test and evaluate new engine health management technologies through the implementation of the Vehicle Integrated Propulsion Research (VIPR) project.
“The VIPR project started in 2010. We’ve had three tests since then. Our first test occurred in December 2011, our second test was in July 2013 and now we’re at our penultimate test in July 2015,” said Paul Krasa, VIPR project manager. “Airliners have encountered volcanic ash in the past and from those encounters we know what has happened. VIPR will investigate and answer is why it happens. The objective of VIPR is to demonstrate engine advanced health management and diagnose potential engine faults before they happen.”
According to Krasa, with the use of a C-17 and two F117 engines provided by the Air Force Research Laboratory, this stage of testing will introduce increased amounts of Mazama volcanic ash into one of the engines to assess how the health monitoring sensors and their associated software can detect and report a problem on the VIPR project.
“We’re looking at technologies that will be able to identify aircraft entry faults at the beginning stages and we want to be able to identify and diagnose them, and also how they will change over time,” said John Lekki, VIPR principle investigator.
How the team will identify and diagnose these issues will rely on the multiple sensors located throughout the engine, according to Lekki.
“We have a vibration sensor that we originally researched for utilization on the space shuttle’s main engine. We wanted to be able to be sure that we’re making credible measurements with the sensor,” Lekki said. “This sensor is unique in that we not only use the sensor measurements to diagnose what’s going on with the engine, but we’re also paying attention to the sensor itself in making sure nothing malfunctions on the sensor itself, so it has an additional capability, which we feel is critical to engine health management.”
In addition to the vibration sensor, Lekki noted the use of a unique high-temperature fiber optic temperature sensor, to include the use of thin film sensors, which go into the compressor. The compressor is one of the higher temperature areas in the engine.
“This sensor was built to be extremely dynamic. It can pick up temperature fluctuations at an extremely fast rate and will be very beneficial as we go to higher pressure ratios,” said Lekki.
A Microwave Tip Clearances sensor will also be added to measure the gap between the outer wall of the turbine and the tips of the turbine blades.
“This is a key measurement in aircraft engines because if we can measure this and measure it precisely, not only can we tell whether or not there are problems with the turbine blades, but we can also look at adding active clearance control which would give us the benefit of having a more fuel efficient engine,” said Lekki. “So it has two benefits that we can see from this technology.”
Turbine blades are one of the most difficult areas to get health management information from due to its location within the engine, according to Lekki.
Additionally, Lekki said emissions sensors were built behind the engine in order to give the team an idea of what’s going on with the combustion process.
“We are very excited to be able to have all these sensors working together so we can detect how the volcanic ash in many ways is affecting the engine real time, so we can also begin to develop the diagnostics capabilities that we want to have in a volcanic ash encounter. And so we can develop a prognosis in order to give folks an idea of how long before [volcanic ash in the engine] is going to be an issue. That’s why we’re really glad to have this capability,” added Lekki.
As for the main component being used to test and degrade the integrity of the engine, Jack Hoyning, Air Force Research Laboratory principal investigator, noted that the team would be using Mazama ash, a compound that is made largely of glass which comes from Oregon, but is also native to California. It is mined on an old, dry riverbed.
“We chose volcanic ash because it’s an interesting way to fault an engine and it’s also something that hasn’t been carefully studied in the past. This ash is very abrasive, highly angular. It has another feature in the sense that if it gets above a certain temperature it will melt and stick to the blades,” said Hoyning.
“What we know about the effects of ash on turbine is limited. For this particular test, we’re going to choose two ash levels. One will be a light level of ash that is invisible to the eye and the other level is a medium level, which you may be able to see depending on the weather conditions that day. Overall, this test will definitely help us take the next step in understanding if we can fly close to these plumes.”
Researchers from four NASA centers will also be involved in various aspects of research and testing – Armstrong, Glenn Research Center in Cleveland, Langley Research Center in Hampton, Virginia, and Ames Research Center in Moffett Field, California.
This phase of VIPR at Edwards AFB will mark the third and final round of testing with three objectives: incorporate smart sensors designed to improve flying safety and reduce costs, detect potential engine faults and evaluate advances in engine diagnostics. The application is expected to benefit both the Air Force and civilian air travel.