"The wing we designed could make substantial differences
in flight safety and airport capacity," said Omer Savas,
professor of mechanical engineering at UC Berkeley. Savas
and former UC Berkeley graduate students Jason Ortega and
Robert Bristol experimented with wing designs that would
quickly render wake turbulence harmless after takeoffs and
UC Berkeley filed a provisional patent application on Friday,
Nov. 16, for the design using results from Savas' experiments.
Federal regulations require two flights to be spaced far
enough apart during takeoff and landing to avoid the potential
hazards caused by wake turbulence. While wake turbulence
alone would not have likely caused the crash of Flight 587
in New York, "turbulence in combination with a possible
structural problem in the tail fin could be devastating,"
Savas has been testing a design with triangular extensions
jutting behind each wing. He has found that with the bat-like
design, the wake vortices generated dissipate two to three
times faster compared with traditional wing designs.
A wake vortex results from the mismatch in speed, direction
and pressure of air moving above and below a plane's wing.
These differences govern the lift generated during flight.
Planes that are large, heavy and moving slowly create stronger
"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," said Savas. "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."
Depending upon weather conditions and the plane's speed
and size, the wake vortices generated are relatively stable
and can stretch a distance of hundreds of wingspans, or
three to five miles for a commercial aircraft, said Savas.
For decades, engineers have sought ways to disrupt the
stability of wake vortices in efforts to transform the forceful
swirls into benign puffs of air. Wing designs have included
small pulsing jets mounted at the wingtips, spars and oscillating
spoilers. Most of the designs have been ineffective or impractical;
some involve moving parts that require greater maintenance.
In tests, Savas' design effectively created instability
in the vortices without generating too much additional drag.
The design also has the benefit of involving no actively
In one of his earlier experiments, reported in April's
American Institute of Aeronautics and Astronautics (AIAA)
Journal, Savas towed tapered sheet metal wings - one a traditional
rectangular design, the other with the triangular flaps
- in a 70-meter-long water tank at speeds of 1.6 meters
per second. Fluorescent dyes marked the vortex wake generated
by the 40-centimeter-wide wings.
Savas found that the traditional wing created two stable,
counter-rotating swirls from the outside tips. In comparison,
the wing fitted with triangular flaps created four vortices,
two from the wing tips and two from the flaps. When the
flap and tip swirls - each rotating in opposite directions
- ran into each other, they quickly became unstable.
"It's like two tornadoes shredding each other," said Savas.
"One is spinning clockwise, the other counter-clockwise,
so each one counteracts the other. But, they first have
to be close enough to each other and have the right strengths
for that to happen. What we're doing with these triangular
flaps is creating a second vortex that's close enough to
destabilize the wing tip vortex."
Savas and his former graduate students have since conducted
several other experiments that have been submitted for publication
in which they refine the geometry of the triangular flaps.
In one test where the flaps span up to half the length of
a wing, the wake turbulence began to dissipate four to eight
times faster than the wake vortices created by the traditional
Test results were duplicated and confirmed with computer
simulations using flow models developed by Philip Marcus,
professor of mechanical engineering at UC Berkeley and an
expert on vortex calculations.
"Our model is a significant improvement over current designs,"
said Savas. "In addition to improving safety, 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
Savas said the design would entail some increased drag,
but it could be easily compensated for with extra engine
thrust during takeoff. After takeoff, the triangular extensions
could be retracted so that drag would not be a factor.
The dynamics of how triangular flaps affect wake vortices
can lead to other applications, Savas noted. For instance,
small triangular flaps fitted to the outer tips of helicopter
blades could significantly cut down on noise generated when
the blades slice through the air.
Savas is currently working on a pilot program with scientists
at NASA Ames Research Center to incorporate the triangular-flapped
wings in aircraft designs. He noted that commercial jets
have not gone through a significant design change since
the Boeing 707 began rolling down the runways in the 1950s.
"Maybe it's time for something new," he said.