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Soaring Science: The Aerodynamics of Flying a Frisbee

An air-bending activity from Science Buddies



George Retseck

Key concepts
Aerodynamics
Forces
Physics
Lift
Drag

Introduction
Are you good at tossing a Frisbee? Have you ever wondered how a Frisbee is able to fly through the air so well? If you can throw a perfect, arcing curve right on target, you've already trained your arm to aid in the aerodynamics of Frisbee flight! In this activity, you'll investigate how the angle at which you throw the Frisbee affects its flight direction and distance. Next time you're out tossing a Frisbee, this little lesson in aerodynamics may help make your throws even more accurate!

Background
Two key forces that act on a Frisbee during flight are lift and drag. Lift is the force that allows the Frisbee to stay airborne, and in flight it opposes the force of gravity on the disk's mass. The Frisbee itself creates this lift force as it flies through the air. Because of the Frisbee's curved shape, the airflow above it must travel at a higher velocity than that underneath, thereby creating low pressure above and high pressure below the disk. This pressure difference provides the lift. Drag is a resistant force on the Frisbee, perpendicular to the lift, and it acts against the disk's movement through the air. The angle at which the Frisbee is thrown, which we'll call the "launch angle" (aka the angle of attack), affects both lift and drag.

As a side note, you've probably noticed that a Frisbee doesn't travel far if it's thrown without spin. Spinning the Frisbee helps it fly by supplying angular momentum, which helps keep the Frisbee stable; the faster it spins, the more stable it should be.

Materials
•     A Frisbee
•     Long string or hose
•     Large open area in which to toss a Frisbee
•     Tape measure
•     A helper (optional)
•     A piece of paper and a pen or pencil (optional)

Preparation
•     Use the long string or hose to make a long, straight line in front of you, at least 7.5 meters long. You will be throwing the Frisbee so that it is directed down this center line.
•     Practice throwing the Frisbee down the straight line a few times so you get used to tossing it. If you have not thrown a Frisbee much before, you may want to try practicing it for a little while. Tip: A good way to throw a Frisbee is by standing sideways with the Frisbee held in front of you (near your non-tossing shoulder), then bringing the disk horizontally across you before you release it.
•     If there is wind during any of your Frisbee throws, note the wind speed and direction.

Procedure
•     Throw the Frisbee as flat and horizontal as you can, aiming it down the center line you made. You can have a helper watch to confirm the angle at which you throw the Frisbee. How far did it travel? How far did it veer from the center line, and in what direction (left or right)? If you have a piece of paper and a pencil or pen, you can record this data and all following flight information.
•     Throw the Frisbee as flat and horizontal as you can at least four more times. Each time throw the Frisbee with similar arm motion and speed, use a similar spin, and have the same release point. How far did the Frisbee travel each time? How far did it travel away from the center line, and in what direction?
•     Throw the Frisbee tilted up a little, at a roughly 45-degree angle above the previous, flat throw. (You can imagine that if your arm were the hour hand of a clock, the previous throw would have been directed toward three o'clock and this throw should aim between one o'clock and two o'clock). Throw it this way at least five times. Other than changing the launch angle, try to keep all other aspects of the flights the same. How far did the Frisbee travel each time when thrown at an upward angle? How far did it travel away from the center line, and in what direction?
•     Throw the Frisbee tilted down a little, aiming at an angle about 45 degrees below a flat throw (between four o'clock and five o'clock), at least five times. Again, try to keep all other aspects of each flight the same. How far did the Frisbee travel each time when thrown at a downward angle? How far did it travel away from the center line, and in what direction?
•     Did you see a consistent relationship between launch angle and flight direction? Is there a relationship between launch angle and distance? Based on aerodynamic principles, why do you think you saw these relationships?
•     Extra: In this activity, you investigated how the Frisbee's launch angle affects its flight distance and direction, but you only tested a few angles. You can try this activity again but test even more angles, such as angles in between the ones you tried in this activity. You can videotape your throws and then watch the video to analyze and confirm the angles at which you threw the Frisbee. How well does the Frisbee fly using other launch angles? Is there an angle that consistently correlates with the "best" flight in terms of distance and stability?
•     Extra: In this activity there was not a focus on the effects of wind on a Frisbee's trajectory, but it can definitely be a factor. How will the Frisbee's flight be affected by throwing it into the wind? What about across or with the wind? How does the launch angle change a flight in each of these conditions?
•     Extra: You could compare the flight of a Frisbee with that of an aerobie (flying ring disk). What differences do you notice? Can you explain them in terms of aerodynamic forces?


Observations and results
When you threw the Frisbee as flat and horizontal as you could, did it generally fly relatively straight (not far to the left or right) and pretty far? When you threw the Frisbee tilted up a little, did it fly pretty high and far but not as straight, going off to the side near the end of its flight? When you threw the Frisbee tilted down a little, did it fly not nearly as far—and did it also go off to the side?

To fly well, the Frisbee needs enough lift, and not too much drag. When the Frisbee is thrown tilted downward, it does not have much lift and so it quickly falls to the ground. When the Frisbee is thrown relatively horizontal, it has a good amount of lift and consequently should fly relatively far—at least much farther than when the Frisbee was thrown tilted down. When an even larger launch angle is used, the Frisbee has more lift. You may have noticed, however, that although the Frisbee thrown upward flew relatively high, it probably stalled out rather abruptly near the end of its flight. This may have caused it to land gently and/or quickly go off to the side. Of the three launch angles tested in this activity, the horizontal launches probably resulted in the overall "best" Frisbee throws in terms of distance and straightness.

More to explore
What Do a Submarine, a Rocket, and a Football Have in Common? from Scientific American
What effect does the rim of a Frisbee have on its flight? from Ask Us Sport! Science at the Exploratorium
The Physics of the Frisbee (pdf) from Katherine Keller at the University of Florida
NASA Glenn Research Center: The Beginner's Guide to Aeronautics from the National Aeronautics and Space Administration
The Physics of Frisbees (pdf) from V. R. Morrison at Mount Allison University, Canada
The "Ultimate" Science Fair Project: Flying Disk Aerodynamics from Science Buddies

 

This activity brought to you in partnership with Science Buddies
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