PENTAGON, Va., April 30, 2018 —
As part of its goal to increase combat capability, Air Force Operational Energy looks holistically at every aspect of aircraft operations and technology for opportunities to optimize energy consumption. Both larger impact initiatives, such as advanced aerodynamics and adaptive jet engines, and smaller impact initiatives, such as compressor blade inspection/optimization and engine washing, are part of the effort to use fuel wisely.
Jet engines ingest debris and contaminants during operations, resulting in erosion of engine compressor blades - a critical aspect of engine performance on the majority of Air Force aircraft. Over time, high pressure and harsh conditions (such as operating in sandy environments) cause deterioration like blade thinning, cracking, and increased blade surface roughness.
Blade defects decrease engine efficiency and power, while increasing fuel burn (specific fuel consumption) and exhaust gas temperature (EGT) - resulting in higher maintenance costs, and decreased aircraft availability. Additionally, defective compressor blades can pose a safety threat if not replaced in a timely manner. While researching areas for increased aircraft optimization, Air Force Operational Energy found that cost-effective and reliable blade inspection ensures engines are performing optimally, and is paramount to maintaining aircraft readiness.
For generations, Air Force maintainers have primarily used a form of manual inspection to look for any visible cracks or breaks in the blade. Fluorescent Penetrant Inspection (FPI), which applies a fluorescent dye to the blade to show where cracks are, has been the most widely used method; however, FPI is time-consuming, costly, and subject to human error.
Recent developments in compressor blade inspection technology drastically reduce time and cost, and are more effective at identifying defects. Sonic Infrared Inspection (SIR) uses ultrasonic waves to gently vibrate the blade and create friction between crack surfaces. In turn, a small amount of heat is produced where cracks exist, which can then be detected using highly-sensitive infrared cameras. By looking at the image, operators can easily pinpoint the crack or defect and determine its severity.
Air Force Research Laboratory (AFRL) tested SIR technology and processes, developed by Florida Turbine Technologies, Inc. (FTT), on compressor blades at the Oklahoma City Air Logistics Complex, Tinker Air Force Base. Project engineers saw many benefits of SIR technology including increased detection speed, increased accuracy (SIR has the potential to detect smaller cracks than FPI, and has a lower incidence of error), environmental factors (SIR does not use toxic chemicals like FPI), and increased cost savings (from not having to replace as many blades). SIR technology is currently being implemented at Tinker Air Force Base, and personnel are being trained and certified on its use.
“Prior to the development of the SIR system, Tinker had no cost effective way of inspecting and repairing engine compressor blades, and returning them back to service,” said Mr. Siamack Mazdiyasni, an AFRL Materials Engineer who serves as a subject matter expert for the program. “As a result, Tinker would scrap over 90 percent of the blades when the blades returned to depot,” Mazdiyasni continued. With the implementation of SIR technology, AFRL estimates over $5 million in annual savings from refurbishing blades and sending them back into service safely.
“While the main purpose of SIR technology is not to reduce fuel consumption, we found it is an added benefit. Making it easier to identify defects in compressor blades also helps detect potential engine inefficiencies,” said Roberto Guerrero, Deputy Assistant Secretary of the Air Force for Operational Energy. “In order for an engine to function at its best, the blades need to be in, and maintain optimal condition, and SIR better allows us to determine that.”
Crack detection is just one method to ensure peak blade performance. Innovative technologies to prevent wear-and-tear, and repair damaged blades (as well as other aircraft parts) are under development by numerous defense and technology companies. Specialized blade coatings, for instance, can be applied directly on the blades to prevent erosion. Blade geometry optimization uses advanced technology to measure each blade and precisely shape it for increased efficiency.
Instead of throwing damaged parts away and replacing them with expensive new parts, what if the Air Force could repair them and put them back on the aircraft safely, while also ensuring maximum performance? Aircraft sustainment is one of several focus areas where Air Force Operational Energy strives to improve readiness and increase combat capability.
Editor's note: The original story can be viewed on the Air Force Installations, Environment and Energy website.