As Man Takes Another Step Towards the Skies, A Look at Bird Flight

birds owe much to lift and wing loading, physics shows

By Jonny Lupsha, Wondrium Staff Writer

A French inventor flew halfway across the English Channel on a skateboard-sized device, according to the BBC News. Franky Zapata aimed to cross the Channel in just 20 minutes but missed his refueling platform by just a few inches, cutting the flight short. He likened it to bird flight, though the physics differs.

The “flyboard” is a small board that a rider steps on and steers. The BBC article says the flyboard is “powered by five small jet engines and fueled by kerosene, which is kept in the rider’s backpack.” In an interview for the article, inventor Franky Zapata said, “We created a new way of flying—we don’t use wings. You are like a bird; it’s your body that is flying.” Ultimately, his invention could bring humankind one step closer to the birdlike flight we’ve reached toward for centuries, with vastly different physics at work.

Lift 101: Bernoulli and Newton

Lift is the simple yet marvelous wonder of flight. From the tiny hummingbird to the massive jet airliner, the ability of flight depends on defying gravity. So how is it done? The shape of the wing forms an airfoil, an asymmetrically curved shape with a longer distance over the top of the wing than the bottom. “A stream of air meets the curved front, and is split into two streams—one above the wing and one below,” said Dr. Bruce E. Fleury, Professor of the Practice in the Department of Ecology and Evolutionary Biology at Tulane University. “The top flow goes up and over the curved front of the airfoil, and as it does so, the streamlines of this flow become pinched closer together as they pass over the top and flow downward over the back of the airfoil.” Dr. Fleury likened this to water entering a narrow canyon, in that the journey causes it to speed up, while the bottom air stream that passes under the wing does not.

“And, thank you, Bernoulli, we know that this increased velocity results in decreased pressure above the airfoil relative to the bottom, which generates lift,” Dr. Fleury said. The mathematical equation known as Bernoulli’s principle explains that pressure and velocity are inversely proportional to each other.

Next, we turn to Sir Isaac Newton’s Third Law. “The wing also generates a resultant upward force by deflecting air downward, as it hugs the downward curve on the top of the airfoil,” Dr. Fleury said. “And that’s Newton’s Third Law at work—for every action there’s an equal and opposite reaction. The downward force generates a reactive upward force that helps to lift the airfoil into the air.”

Wing Loading

Birds often display very different methods of flight from one species to another, but why? “The style of flight is determined by the size of the bird and the shape, its bill, its feet, its wings, all these traits that are adaptations to the bird’s lifestyle,” Dr. Fleury said. “In other words, who you are equals how you fly.”

Dr. Fleury explained that the relationship between wing size and the size of the bird is called wing loading. “Wing loading equals the ratio of body weight to wing area,” he said. “Birds like vultures, with large wings relative to their weight, have low wing loading, so they can soar for long periods. Heavier birds with smaller wings, like loons and grebes and many ducks, have high wing loading, so they have to run across the water’s surface to launch, and flap very energetically to get airborne.”

Franky Zapata has already said he’ll make a second attempt to cross the English Channel on his flyboard sometime this week. Should he succeed, humanity could be looking at a new method of flight—and unless we sprout wings, it may be the least cumbersome practice we ever develop.

Dr. Fleury is Professor of the Practice in the Department of Ecology and Evolutionary Biology at Tulane University

Dr. Bruce E. Fleury contributed to this article. Dr. Fleury is Professor of the Practice in the Department of Ecology and Evolutionary Biology at Tulane University. He earned a B.A. from the University of Rochester in Psychology and General Science, an M.A. in Library, Media, and Information Studies from the University of South Florida, and an M.S. and a Ph.D. in Biology, both from Tulane.