Underwater Travel Takes Wing
By David Snow, Wired News
Mar. 03, 2004
 
The U.S. Navy plans to begin testing a prototype for an unmanned
underwater glider with a flying-wing design in March, according to the
Office of Naval Research, which funds the project.
 
If successful, tests of the Flying Wing Underwater Glider could lead to a
new generation of gliders that researchers expect to be the largest and
fastest to date. They would be capable of traveling thousands of miles
under ocean waves, quietly conducting surveillance and gathering data for
military and civilian purposes, researchers said.
 
"Gliders have the potential of providing long-endurance mobile platforms
for employing sensors," said Thomas Franklin Swean Jr., team leader for
Ocean Engineering and Marine Systems Science and Technology at the Office
of Naval Research, which has spent $500,000 on the project so far. "The
endurance is measured in months rather than hours or days."
 
The Flying Wing isn't the first glider to "fly" underwater, just the
first of its kind. Over the past seven years, projects at the Scripps
Institution of Oceanography, the University of Washington School of
Oceanography and Woods Hole Oceanographic Institution have developed
gliders whose designs incorporate torpedo-like shapes. The new wing
design, akin to that of a B-2 stealth bomber, could be superior to them
in some ways but inferior in others, sources said.
 
New craft based on the flying-wing prototype, which has a 20-foot
wingspan and a theoretical top speed of 5 nautical mph -- 10 times the
speed of existing gliders -- might be effective in the open sea, but
their size could hinder them in shallow waters and make them more
difficult to deploy than existing gliders.
 
The Flying Wing Underwater Glider's likely civilian applications include
ocean science research, environmental study and fisheries monitoring,
Swean said. It could map currents or follow marine animals without
disrupting their behavior, according to Scott Jenkins, a senior engineer
at Scripps who spearheaded work on the glider's design.
 
Jenkins described two scenarios in which the glider could play a vital
role. In the first, oil companies use it to monitor the activity of sperm
whales. The industry's use of seismic refraction shootings to detect
undersea oil deposits -- explosions are detonated and the resulting shock
waves are studied -- is restricted when whales are nearby. In the second
scenario, a glider monitors an offshore waste field to help determine its
relationship to beach closures.
 
"Nothing else is capable of doing that (kind of research) in an
economical way," he said, pointing out that the use of ships is
expensive, whether data gathering is carried out onboard or the ship is
hired as a delivery vehicle for instruments on moorings. Moorings are
susceptible to damage from storms, ship collisions and vandalism.
 
The glider's other major applications are military, Swean said. They
include surveillance and reconnaissance. "Homeland security applications
would involve coastal monitoring, perhaps ship traffic," he added.
 
In the future, gliders could take on other roles, such as payload
delivery. "We're talking very large gliders," Jenkins said. "One
practical thing would be to move underwater robots (vehicles) around. All
of those devices have a mother vehicle. A glider could do it in a very
clandestine way."
 
The Navy's tests scheduled for March will take place in a vast basin at
Space and Naval Warfare Systems Center in San Diego. Tests scheduled for
April will take place at sea off Point Loma, which lies between San Diego
Bay and the Pacific Ocean. Precise test dates have yet to be determined,
but the goals are clear.
 
"These are basic tests to validate hydrodynamic design," Swean said. "We
will observe glide trajectory at a prescribed net buoyancy to confirm the
wing is flying as designed. Subsequent phases will integrate sensors and
prove endurance (and) range."
 
The prototype wing, built by Legnos Boat Building of Groton, Connecticut,
is 1.3 feet thick and made up of fiberglass covering foam ribs, Swean
said. Inside the glider, a steel pressure hull will protect inner
workings during deep-sea diving, Jenkins added. The internal volume of 40
cubic feet will be enough space for control systems and research
instruments.
 
The most essential control system is the buoyancy engine, which uses
battery power to drive the wing, Jenkins said. It powers a high-pressure
pump that inflates a bladder, which displaces enough water to cause the
glider to rise. Evacuating the bladder displaces less water and causes
the glider to descend.
 
As Swean described it, the wing moves forward when changes in its
buoyancy create vertical forces; the wing uses the pressure of the
water's mass to transform those forces into forward movement. In other
words, it moves forward by changing its elevation. Jenkins added that the
onboard computer will adjust the craft's center of gravity by sliding the
batteries along a track, which will also help with steering.
 
The new design's potential superiority over existing underwater gliders
involves the efficiency of the wing shape, Jenkins said. With nearly all
of the surface area creating lift, the vehicle can travel over long
distances using only a small amount of energy.
 
"The wing is the most efficient shape we know," Jenkins said. "The
prototype for it is a bird. Nature's the most demanding of all
engineers."
 
The glider will surface to transmit data to a satellite or stay submerged
to send acoustic communications, Swean said.
 
The Navy isn't the only party interested in the outcome of the
flying-wing glider tests.
 
"We will certainly follow what Scott (Jenkins) has done and look into the
capabilities of that (glider)," said Clayton Jones, a project engineer
with glider manufacturer Webb Research.