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.
Why?
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."
Seagull Plane?
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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