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Vanderbilt Engineering to lead FAA
helicopter reliability project
NASHVILLE, Tenn. -- All it took to rip the roof off Aloha Airlines Flight 243 in
1988 was the gradual corrosion around rivet holes that had, over time, created
tiny cracks in the Boeing 737's fuselage that suddenly combined with fatal
results.
That incident, which caused one death, 65 injuries and a traumatic open-air ride
in an airplane convertible for the rest of the passengers, sparked two decades
of national programs designed to make aging airplanes more reliable.
Now the Vanderbilt School of Engineering is leading a new Federal Aviation
Administration program to apply and expand aging aircraft reliability techniques
to helicopters. Although the project is focused on helicopters, researchers
believe much of what is learned could be applied to other types of aircraft.*
*The five-year, $1.5 million
project will be kicked off in a project team meeting to be held Nov. 27-29 in
Atlantic City, N.J.
Helicopter safety has become an increasing concern in recent years because the
number of emergency medical service helicopter accidents in the U.S. nearly
doubled from the mid-1990s to 2004. Although most of these accidents were caused
by challenging weather, difficult terrain conditions and pilot error, the FAA
wants to ensure that the equipment gives pilots every advantage.
"The margin for error in flying a helicopter, especially in rescue missions, is
very slim," says project principal investigator Sankaran Mahadevan. "We want to
make sure that helicopter pilots don't have to deal with equipment failure, such
as metal fatigue, on top of the challenges of shifting winds, unseen obstacles
like power lines, birds
flying into the blades, and space limitations of maneuvering in tight spots."
As the aviation industry moves towards using new, lighter materials in their
designs, more understanding is needed about the characteristics and performance
of these materials under various operating conditions, said Mahadevan, professor
of civil and environmental engineering.
"Lighter materials can translate into fuel economies," Mahadevan said, "But the
industry needs more data on how these new materials will perform over time. We
are going to help develop that knowledge base to guide rotorcraft design as well
as maintenance schedules."
Mahadevan and his team at Vanderbilt will work with subcontractor Bell
Helicopter Textron, Inc. of Fort Worth, Texas, to test the mettle of the
materials used in helicopter components.
"In addition to needing information about the materials, we need better
understanding of how the entire structure of a helicopter functions under a
variety of performance requirements," Mahadevan said. "Helicopters have complex
structural geometry and are subject to a variety of loading conditions, even
without taking into considerations the unknowns involved with the new
materials."
The team's first step will be to do controlled laboratory tests on new materials
to get an idea about how and where cracks and other flaws will materialize under
various conditions.
This data will be leveraged to predict the materials' behavior throughout the
life of the aircraft, using various computer models, including computer
simulation and probability software. These and other computational tools will be
used to determine how a helicopter would most likely to be affected by failures
within various components.
"Finally, this information will guide us in recommending inspection and
maintenance schedules," Mahadevan said. "The FAA wants to create the optimal
schedule of inspection and maintenance to ensure against catastrophic failure
without wasting resources by redundant inspections."
Mahadevan said that Bell Helicopter Textron will be an integral part of the
project. The company, which produces a wide range of commercial and military
helicopters, will contribute data on helicopter components and materials, as
well as on how the defects grow in size. The company will also advise Vanderbilt
researchers on useful and practical demonstration problems with which to test
the research.
"This research differs from most studies on helicopter damage tolerance in that
it will incorporate uncertainties in geometry, material behavior, mission
operations and initial flaw distribution within the rotorcraft components,"
Mahadevan said. "As in the Aloha Airlines accident, sometimes more than one flaw
can interact, causing catastrophic results."
The computing methods to be used in the research have been used in a variety of
other risk and reliability applications for automotive, spacecraft and aircraft
components, but this is the first time they have been applied to helicopter
components and materials. In addition to providing a risk and reliability
foundation for helicopters, the
research project will refine and expand the computing methods, Mahadevan said.
"It has been shown that different models will yield very different predictions,"
he said. "One possible way to reduce modeling error responsible for these
variations is to develop and validate a more accurate and efficient model.
"In the past few years, our group has been successful in developing such models
for complex fatigue and fracture, which have shown excellent performance for a
wide variety of materials. The FAA project will build on this success and will
have strong impact on design methods and risk management."
Contact:
Vivian Cooper,
(615) 343-6314
vivi.cooper@vanderbilt.edu
or
David F. Salisbury,
(615) 343-6803
david.f.salisbury@vanderbilt.edu |
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