Underwater Gliders

Science - AP

New Robotic Gliders Can Soar Under Water
Sun Nov 23, 1:17 PM ET

By ANDREW BRIDGES, AP Science Writer

SAN DIEGO - A century after the Wright Brothers first took to the skies, the
world of flight is pushing to new depths.

Researchers are perfecting innovative gliders that can swoop and soar on
journeys covering hundreds of miles and lasting for weeks — all deep beneath
the ocean waves.

The fledgling technology, barely a decade old, has already produced robotic
submarine gliders that move slowly, with the nimbleness of a blimp. Now
next-generation gliders are being developed to fly just as gracefully as their
airborne counterparts, diving and climbing on broad wings that slice not air
but water.


"They're coming of age," said Clayton Jones, project engineer at Webb Research
Corp., an East Falmouth, Mass., company that has sold 21 of the $60,000 ocean
gliders it builds.


The submarine robots don't use propellers, jets or flapping wings to get about.
Nor do they swim.


Instead, they pump ballast water in and out to subtly change their buoyancy.
That enables them to alternately rise and fall through the ocean as they glide
forward.


The battery-powered gliders have quickly lured the interest of marine
scientists who have fitted early models with instruments that measure ocean
currents, salinity and temperature. Scientists hope that eventually the gliders
could be used to monitor pollution levels, keep tabs on plankton blooms and,
quite literally, "swim with the fishes" or other prey.


"They could follow schools of fish — or Russian submarines," said Scott
Jenkins, an engineer and glider expert at the Scripps Institution of
Oceanography in San Diego.


The gliders are as efficient as they are stealthy, which has drawn the interest
and backing of the U.S. Navy (news - web sites). Potential military
applications include mine detection, surveillance and patrol, Navy officials
said.


The Navy hatched the glider concept in the early 1960s but the idea soon lost
ground to propeller-driven submersibles. The idea was proposed again in the
late 1980s when engineers realized the technology could spawn thrifty gliders
that could embark on watery flights lasting months and miles at a time.


"What they bring to the table is a persistence, a long-term deployment
capability," said Thomas Swean, team leader for ocean engineering and marine
systems at the Office of Naval Research in Arlington, Va.


The aerodynamic principles that guide ocean gliders are the same that apply to
airborne gliders, except the underwater versions can climb every bit as
effortlessly as they dive.


An important stage in glider development came last summer, when scientists
deployed 15 of the robots in Monterey Bay in the first large field
demonstration of the technology.


"We've just handed the adolescents the car keys," Jones said. "They're driving
around the block and they're doing what are the first glimpses of what we hope
to accomplish."


Still, Jones acknowledges that expectations for these autonomous underwater
vehicles, or AUVs, have to be reined in for now.


Problems include the build up of barnacles on long flights, which create drag.
At the surface, ships, kelp and curious fisherman also pose risks, said Ralf
Bachmayer, a Princeton University glider researcher.


During the August experiments in Monterey, fishermen plucked four of the
gliders from the water after the robots briefly surfaced to communicate with
scientists by satellite. Three of the gilders were recovered intact; the fourth
was found on shore in pieces.





The first generation of gliders look like little more than 6-foot torpedoes
fitted with stubby wings that provide the lift needed to move them forward.

For now, experts concede the early robots, built by Scripps, Webb Research and
the University of Washington, are basically glorified underwater blimps capable
of flights measured in weeks and hundreds of miles.

But engineers designing the next generation of gliders promise huge gains in
efficiency, range and speed. Assisting them is the more than 100 years of
studies on aerodynamics undertaken since the days of Orville and Wilbur Wright.


"There are no new principles being invoked here," Swean said. "The sea is a
very, very harsh environment but it is a fluid. Air and water, except for their
densities, are very similar creatures."

The boldest new ocean glider is a large flying wing the Navy is developing with
Scripps that should be more B-2 than blimp.

Engineers hope to begin testing the 20-foot, delta-winged prototype this
February off the San Diego coast.

Preliminary analysis of the design suggests its shape should produce speeds up
to 10 times as fast as today's gliders, which fly at a pokey half-mile an hour.
It also should fly more efficiently than its torpedo-shaped predecessors.

Other varieties of glider, now being tested, will be even more efficient and
forgo the use of batteries altogether. Instead, they will draw their power from
the ocean itself, gathering energy from the warmth of the water around them.

"It's like an external fuel tank," Jenkins said. "It's everywhere you go and
you just have to sip from it."

Such self-sustaining gliders, according to the Navy, could undertake missions
that span as many as five years and thousands of miles.

___

On the Net:

Webb Research Corp.: http://www.webbresearch.com

Office of Naval Research: http://www.onr.navy.mil