As investigators
diligently work to determine the chain-of-events that brought down
American Airlines flight 587 on November 12 just a few miles from
New York's John F. Kennedy airport, a UC Berkeley researcher has
proposed a solution to one long-standing engineering problem that
may have contributed to the crash.
Moments after takeoff, the Airbus A300 jet twice hit turbulence
from the wake of a Boeing 747 just ninety seconds ahead of it.
While it's unlikely that the turbulence alone tore the tail off
the plane, the violent airflow "certainly triggered the crash,"
says UC Berkeley Mechanical Engineering professor Omer Savas.
Savas and his colleagues' idea is to snuff out the tiny tornadoes
generated at the wing tips by adding two more vortices rotating
in opposite directions.
"It's like two tornadoes shredding each other," Savas says.
"One is spinning clockwise, the other counter-clockwise, so the
pair counteract each other."
Savas and former graduate students Jason Ortega and Robert Bristol
demonstrated the canceling effect with a new wing design that
features triangular flaps jutting out the back of each fin. According
to the researchers, the additional vortices generated by the triangles
help dissipate the usual wake vortices two to three times faster
than with traditional wing designs. On November 16, UC Berkeley
filed a provisional patent on the concept based on the results
from Savas's experiments.
In
tests, the wing design with triangular flaps extending behind
it significantly cut wake turbulence compared with traditional
wing designs.
(Click for larger
image.)
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"The wing we designed could make substantial differences in flight
safety and airport capacity," says Savas, who put his models to
the test in a 70-meter-long water tank where airflow can be simulated.
"Cutting the distance that the wake vortex remains coherent would
allow planes to take off and land closer in time together without
compromising safety. That leads to more efficient use of runway
capacity, a major problem at congested airports around the country."
Wake vortices are caused by the mismatch in speed, direction
and air pressure above and below a plane's wing. The air spiraling
behind the tips of the wings can stretch several miles, depending
on the size of the aircraft.
Bruce
Cook photo
Savas
conducts wind-tunnel experiments with scale models of airplane
wings to gather data on vortices that form close behind
the wings.
(Click for larger image.)
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"On a very clear, dry autumn day, you can actually look up with
binoculars at planes in the sky and observe the behavior of these
wake vortices," Savas says. "The water vapor from the engine gets
trapped at the center of the vortices and marks them as a pair
of thin lines in the sky."
Unlike previous proposed solutions to the vortex problem - including
wings outfitted with pulsing jets and oscillating spoilers - Savas's
approach doesn't require moving parts that may fatigue. On each
wing, the triangular flap by itself creates a vortex that destabilizes
the vortex beside it.
Additional experiments showed that when the triangular flaps
were increased in size to span half the length of the wing, the
wake turbulence dissipated four to eight times faster than the
vortices caused by standard wings. Computer simulations developed
by Savas's colleague, professor Philip Marcus, confirmed the test
results.
NASA Ames Research Center is currently exploring other wing/body
configurations based on Savas's research that may someday bring
the turbulence-snuffing science out of the laboratory and into
the sky.
"Our wing is one way of doing it," Savas says, "but perhaps
not the only way."
Omer Savas's
home page
Triangular-Flapped
Aircraft Wing Designed by UC Berkeley Researchers Significantly
Reduces Wake Turbulence by Sarah Yang, UC Berkeley Media Relations
National
Transportation Safety Board investigation into the crash of American
Airlines Flight 587
In
his experiments, Omer Savas used fluorescent dyes to mark
the wake vortices created by a triangular-flapped wing.
The tests in the water tank at UC Berkeley's Richmond Field
Station were filmed.
