Seagulls May Inspire New Airplane Wings, Scientists Say
for National Geographic News
|October 24, 2006|
Want to see the future of flight? Then visit the beach.
Scientists have found that airplane wings shaped similarly to those of some seagulls may reduce drag during flight.
Drag reduction saves fuel, explains Barry Lazos, an aeronautics research engineer at the NASA Langley Research Center in Hampton, Virginia.
"We can reduce drag [with existing technology], but many techniques are often costly and impractical," he said. "Our idea was to look to nature for feasible techniques that might provide significant drag reduction."
He and his colleagues studied creatures that propel themselves through air and water, which are both fluids, for inspiration. (Related: "Quieter Aircraft Takes Cues From Birds, NASA Expert Says" [August 22, 2006].)
"If we saw an interesting characteristic, say a wing shape or a perturbation at a certain location, then we might consider using that in a wind-tunnel test," Lazos said.
The researcher said the approach was a "shot in the dark" because the team did not know beforehand how fluids would flow around the shapes modeled and tested in the wind tunnel.
"The idea was to determine if we can get a drag benefit and then study the flow characteristics to see if we can make further improvements," he added.
The wing designs tested included two that were inspired by seagull wings, one with features found in the back and tail fins of great white sharks, and a wing with features found on the pectoral fins of humpback whales.
The wing inspired by a seagull in gliding flight proved to have the greatest drag reduction—a 4 percent improvement over the theoretically best conventional aircraft wing.
The wing is highly cambered in the span-wise direction—in other words, there's a bend along the length of the wing and the tips point down (see image at left), says Ken Visser, a research collaborator and associate professor of aeronautical engineering at Clarkson University in Potsdam, New York.
Visser is currently on sabbatical at the Institute of Aerodynamics and Flow Technology in Braunschweig, Germany. He is performing computer modeling to optimize the wing-design concept and determine if seagull-inspired wings are applicable to aircraft.
Eye of the Vortex
Wings allow birds and planes to fly by creating a difference in pressure between the top and bottom of the wing. This generates lift.
But where the wings end, there is an abrupt change in lift, Lazos explains. This creates a vortex, or a whirling mass of air similar to a miniature hurricane tilted on its side.
"This swirling vortex trailing from the wing tip creates a downwash of air behind the wing," he said.
The vortex changes the wing's lift characteristics and produces a component of drag called lift-induced drag, he adds.
Lazos and Visser are looking for wing shapes and features that alter the vortex so that it creates less lift-induced drag on the wing.
When they tested the wing modeled after the seagull in high-speed gliding flight, they observed significant drag reduction.
Lazos said investigations at this stage are "very preliminary" but do suggest an answer: "The vortex was pushed outboard of the wing tip [farther from the body of the aircraft]. That might be the reason why it got the benefit it did."
On conventional aircraft wing configurations, he explained, the vortex moves closer to the fuselage.
Visser said that if the vortex is moved further outboard of the wing, instead of over the wing as in conventional designs, "the impact of flow over the wing is a little less, which makes the drag a little less."
Lazos says aircraft with seagull-like wings won't be taking off anytime soon.
For one, NASA's mission and funding has been redirected to space exploration.
But Visser said he is pursuing the concept "full steam ahead" in Germany.
Among the questions to consider are the optimal shape of the wing and how it interacts with other aspects of the airplane design such as weight, structure, stability, and propulsion.
"The question really becomes, Is what we are seeing aerodynamically a benefit for the entire aircraft?" Visser said.
"Aircraft design is not an optimized design of one particular aspect so much as a compromised design of the different disciplines," he continued. "Every area has to give a little from what they view would be the ideal thing."
For example, a wing design that reduces drag but weighs more could be a detriment to the overall aircraft design.
Ultimately, the researchers are attracted to seagulls for more than drag reduction. The birds are highly maneuverable: They can hover, turn on a dime, and swoop down for attack nearly instantaneously with micro-adjustments to their wings.
Applying such maneuverability to aircraft requires new materials that are pliable enough to change shape but rigid enough to support the forces generated during flight.
According to Lazos, "That's a difficult hurdle to jump."
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