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NASA researchers are studying insects and
birds, and using "smart" materials with uncanny properties to develop
new and mindboggling aircraft designs.
by Patrick L.Barry
The "personal aircraft" that replaces
the beloved automobile in people's garages may still lie in the
realm of science fiction or Saturday-morning cartoons, but researchers
at NASA's Langley Research Centre. (LARC) are developing exotic
technologies that could bring a personal "air-car" closer to reality.
And air-cars are just the beginning.
Self-healing wings that flex and react
like living organisms, versatile bombers that double as agile jet
fighters, and swarms of tiny unmanned aircraft are just a few of
the science-fiction-like possibilities that these next-generation
technologies could make feasible in the decades ahead.
At the core of this impending quantum
leap in aerospace technology are "smart" materials -- substances
with uncanny properties, such as the ability to bend on command,
"feel" pressure, and transform from liquid to solid when placed
in a magnetic field.
"This is technology that most people
aren't aware even exists," said Anna McGowan, program manager for
the Morphing Project at LARC, which develops these new technologies.
The task of the Morphing Project is
to envision what cutting-edge aerospace design will be like 20 years
from now and begin developing the technologies to make it happen.
Image courtesy of Robert C. Byrd National Technology
Transfer Centre. Tomorrow's
airplanes could have self-bending wings, which might operate
without flaps --thus reducing drag and saving on fuel costs.
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For example, a personal air-car needs
to be compact, yet able to fly at both very low and very high speeds.
"We know that to get a 'Jetsons' vehicle,
you're probably going to need a wing that can undergo a radical
configuration change," McGowan said. "The kind of wing you need
at very low speed and the kind of wing you need at high speeds are
completely different."
Some airplanes today can already reorient
their wings, such as the Navy's F-14 Tomcat and the B-1 supersonic
bomber. These planes use rigid wings mounted to large, heavy pivots
in the plane's body.
In contrast, Morphing Project scientists
envision a wing that will unfurl on command using "shape-memory"
metal alloys or other novel "smart" materials. The material of the
wing itself would bend to create the new shape.
Shape-memory alloys have the unusual
property of snapping back to their original shape with great force
when a certain amount of heat is applied. Any shape can be "trained"
into the alloy as its original shape.
Among the exotic "smart" materials
being developed by the Morphing Project, shape-memory alloys are
relatively ordinary.
Imagine seeing a bullet shot through
a sheet of material, only to have the material instantly "heal"
behind the bullet! Remember, this is not science fiction. Self-healing
materials actually exist, and LARC scientists are working to unravel
their secrets.
NASA This thin,
flexible film contains a piezoelectric material that responds
to the bend by producing a voltage that's detected by the
electrodes seen at the bottom left of the image.
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"What we did at NASA-Langley was basically
dissect that material to answer the question, 'how does it do that?'"
McGowan said. "By doing so, we can actually get down to computational
modelling of these materials at the molecular level."
"Once we understand the material's
behaviour at that level, then we can create designer 'smart' materials,"
she added.
LARC is also developing customised
variations of piezoelectric materials. These substances link electric
voltage to motion. If you contort a piezoelectric material a voltage
is generated. Conversely, if you apply a voltage, the material will
contort.
Scientists can use such properties
to design piezoelectric materials that function as strain sensors
or as "actuators" -- devices that create small motions in machines,
like the moving of wing flaps.
Combined with micro-electronics, these
materials could lead to a radical advance in airplane design.
"When we look 20 years into the future,
we see airplanes that have distributed self-assessment and repair
in real time," McGowan said.
"To make this technology possible,
you would need to distribute these actuators and sensors throughout
the wings. That's similar to how the human body operates. We have
muscles and nerves all over our bodies -- so we are aware of what's
happening to our bodies and we can respond to it in a number of
ways."
The resemblance to biology doesn't
end there. One avenue of Morphing Project research is to examine
how nature does the things that it does well. Scientists hope they
can learn lessons from this tutelage to improve their own designs.
"Nature does some things that we can't
even get close to doing. Birds are so much more manoeuvrable than
our airplanes are today. Birds can hover, they can fly backwards
and sideways. And insects -- oh forget it! -- upside down, loop-de-loop,
all sorts of things. We can't even get close to that [yet]," McGowan
said.
Called "biomimetics," this practice
of learning from nature has led to the development of -- among other
things -- a facsimile of bone.
Bone is very light because of its porous
interior, but it's also very strong. LARC scientists can make structures
similar to bone by injecting polymer microspheres into composite
shells of the desired shape, then heating the spheres to make them
fuse together like tiny soap bubbles.
NASA LARC scientists
are studying nature to understand how birds and insects achieve
their high degree of efficiency and manoeuvrability.
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"If you can have the strength and lack
of weight of these bone-like structures that I'm talking about,
then add in nerve-like sensors and these flexible actuators, what
you're going to end up with is an extremely lightweight, very strong,
self-sensing, self-actuating structure."
Compare that vision to the rigid, numb,
heavy structures airplanes are made of today, and you'll get a sense
of the dramatic difference "smart" materials could make in aerospace
design.
As with all basic science, the applications
of these "smart" materials will extend to technologies outside of
the aerospace industry.
"We are working very closely with two
different commercialisation groups funded by NASA," McGowan said,
"and the outlook for this technology is on the order of millions
of applications."
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