# Ask A Scientist

### What makes birds fly? Is it the stuff on their feathers?

Asked by: Liam Fontaine
School: Our Lady of Sorrows-Seton Middle School
Grade: 2
Teacher: N/A
Hobbies/Interests: Bike riding, fishing, camping, hiking, tennis and swimming
Career Interest: Paleontologist and Helicoptor Pilot

### Answer from George Catalano

Professor of Mechanical Engineering

Research area: Turbulence, Fluid mechanics, Aerodynamics, Impact of technology upon the environment, Engineering ethics

Professional Experiences:
Fulbright Scholar, Politecnico di Torino, Turin, Italy, 1984
Fulbright Scholar, University of Erlangen, West Germany, 1988.
NASA Fellow, Goddard Institute for Space Sciences, New York City, 2003
Faculty member at Louisiana State University and the United States Military Academy
Captain, USAF, Vietnam era

PHD School:PhD, Aerospace Engineering, The University of Virginia Family: Married with two Alaskan Malamutes and two more in our hearts

Interests/hobbies: : All things Italian, philosophy, cosmology, grand prix racing, writing, painting

Web page

The ability of birds to fly has captivated humankind’s imagination for centuries. Leonardo DaVinci, the great artist, scientist and engineer of the Italian Renaissance once wrote: "...and once you have tasted flight, you will walk the earth with your eyes turned skyward, for there you have been and there you long to return." In fact there are two main types of flight which birds exhibit: gliding and flapping. Birds glide when they use their wings to generate lift, an upward force that counteracts gravity. Lift is the same force that allows airplanes to fly. How do they generate the lift? The principle is referred to as the Bernoulli principle. You can visualize this principle in an easy way. Take a sheet of loose-leaf paper, hold it at two corners and then blow over the top surface. As you blow, the paper will actually move upwards or lift. The air that moves across the top of the paper is moving faster than the air below the paper. Pressure is related to the speed of the air so the faster moving air on top has less pressure associated with it than the bottom slower moving air. It is the pressure difference that pushes the paper upward.. This principle works for birds as well as for Boeing 747s and for the NASA space shuttle. The other type of flight which birds exhibit is flapping. Flapping is a motion used by birds to cover short distances because it requires an incredible amount of energy. There are two main components to the flapping motion. The first is the downward stroke, which generates the lift (as discussed before) and the propulsion. Propulsion is the force that propels the bird forward in a same way as the jet engine propels an aircraft forward. The second is the upward stroke which is used by the bird to return its wings back to their original position so another downward stroke is possible. Birds are able to change direction using not only their wings which can be tilted but also their tails, again much like aircraft. In fact, birds are incredibly more sophisticated and efficient in flight than any aircraft ever developed. One other important element of bird flight is the feather. The purpose of the feathers is to create a smooth surface both over the body of the bird as well as the wings. A smooth surface has less drag so the birds can fly faster and farther for longer periods of time. So the next time you are outside and are fortunate enough to spot a hummingbird hovering near a spring flower or a formation of Canadian geese heading back to upstate New York for the summer, think about the incredibly efficient and magical design you are watching in motion.

Last Updated: 9/18/13