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New Mexico State University

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NMSU, Sandia team up to make air travel safer

New Mexico State University's College of Engineering and Sandia National Laboratories in Albuquerque have teamed up once again to help improve the safety of air travel. A device designed by members of Sandia's Airworthiness Assurance Center and manufactured at NMSU's Advanced Manufacturing Center will test helicopter rotor hubs for their strength and durability.

These hubs hold helicopter blades on the rotors, explained Dennis Roach of the Airworthiness Assurance Center, which is operated by Sandia Labs for the Federal Aviation Administration. Although traditional hubs are made with aluminum or steel and move with bearings, new bearingless hubs made of fiberglass have been developed, Roach said. He said the hubs are created by applying about 250 thin layers of fiberglass, crossing sections in different directions with no air gaps. The resulting hubs are lighter and stronger, but also flexible, requiring fewer moving parts in the rotor control assembly, he said.

Because the technology for these hubs is still new, and because the hubs must undergo large amounts of stress even during normal operation, a method for testing the structural integrity of the hubs was needed. That's where the new testing device came in. Made of steel up to an inch thick in places and weighing about 6,000 pounds, the frame will allow Sandia researchers to test the hubs to determine how much stress and fatigue they will handle before flaws initiate in the fiberglass parts. That way the researchers can assess the technology that already has been developed and see how they can improve it.

"The fixture will simulate the loads and stresses the hubs would receive in the field," Roach said. The device will pull outward on the hub, duplicating the centrifugal force experienced while spinning. It also will dynamically twist the hub back and forth to simulate the forces created by pitch change and aerodynamic resistance against the blades as they rotate, he explained. The forces will be applied simultaneously over millions of fatigue cycles.

The testing fixture was built for Sandia at NMSU's Advanced Manufacturing Center, a fully operational manufacturing facility within the College of Engineering that pairs full-time staff, often with experience in engineering fields, with students in various disciplines at NMSU. About 10 students and three full-time staff worked for four months to complete the helicopter test device, estimated Greg Moran, AMC program manager. "It was a tough job," he said. "Sandia's requirements were quite demanding."

Some parts had to be machined to tolerances within one thousandth of an inch. Proper alignment was another big issue. Because multiple parts of the frame must be parallel, intersecting with others that are perpendicular, the parts had to be created to form very exact angles. "The pieces must all align and the final product must be precise for this machine to operate properly," Roach said.

This is the second project the AMC has completed for Sandia's Airworthiness group in about two years. The first project involved simulating corrosion in airplane panels. It was a difficult project, Roach said, because the material was very thin to begin with, then small sections of the material had to be mechanically removed in certain places, making it even thinner.

Roach and his colleagues were pleased with the initial results from the AMC, so when they needed manufacturing help with their next project, they came back. "They have excellent attention to detail and work hard to address their customer's concerns," Roach said.