Hi,
Flying sports discs (most often referred to by the name of the most
popular brand, Frisbee) receive lift from the fact that they are
shaped something like an airplane wing. Rotation doesn't change that
shape, but it does stabilize the disc. Without the rotation, the disc
would be unstable and would be unable to tack advantage of its
aerodynamic shape. The better it can stay in an aerodynamic position,
the better and longer the disc can fly.
Much of the weight is in the outer rim, so as it is spinning it will
stay in roughly the same orientation in order to preserve angular
momentum. The effect is much the same as is used in gyroscopes, and
the effect is also what makes it possible to ride a bicycle without
falling over.
Here are some resources that explain this concept further.
Frisbee
"The shape of the Frisbee generates lift, but it needs more than that
for flight. Try throwing a Frisbee without spinning it. Notice how it
wobbles and tumbles. The shape of the Frisbee may be generating lift,
but the Frisbee is unstable. It cannot stay upright and eventually
stalls (falls). All flying things must have something which makes them
stable during flight; airplanes and birds have tails, rockets have
fins. For a Frisbee it is the spinning motion generated from the
Frisbee throw, which stabilizes the Frisbee as it flies."
http://wings.avkids.com/Book/Sports/advanced/frisbee-01.html
Disc-Wing Aerodynamics
"A disc wing is a simple type of flying object most commonly
encountered as a frisbee sports disc. A non-spinning, uniform disc
such as a frisbee is neutrally stable in roll but unstable in pitch.
This means that aerodynamic pitching moments during flight tend to
cause the disc to tumble. If the disc is spun, the gyroscopic effect
increases the effective pitch inertia and prevents the disc tumbling
in flight."
http://www.eng.man.ac.uk/Aero/wjc/Research/DiscWingAerodyanmics/DiscWingAerodynamics.htm
Frisbee Physics
"Spinning the Frisbee when it is thrown, or giving it angular momentum
(gyroscopic inertia), provides it with stability. Angular momentum is
a property of any spinning mass. Throwing a Frisbee without any spin
allows it to tumble to the ground. The momentum of the spin also gives
it orientational stability, allowing the Frisbee to receive a steady
lift from the air as it passes through it. The faster the Frisbee
spins, the greater its stability."
http://www.mansfieldct.org/schools/mms/staff/hand/Flightfrisbee.htm
Turbulence created by rotation can also be a factor:
The Flight of the Frisbee
"And the tiny ridges on the Frisbee's top surface introduce
microscopic turbulence into the layer of air just above the label.
Oddly enough, this turbulence helps to keep the upper airstream
attached to the Frisbee, thereby allowing it to travel farther."
http://www.sciam.com/article.cfm?articleID=000155A0-6D59-1C71-9EB7809EC588F2D7
If you'd like some highly technical information about the aerodynamics
of flying discs, including links to informative diagrams, check out
the following site:
Advancements in Flying Disc Research
"This webpage is a resource for easy access to the work that we are
doing as part of a program to develop an Unmanned Air Vehicle (UAV)
based on a spin-stabilised axi-symmetric flying disc. The material
available is of a somewhat technical nature, which is most relevant to
those with a background in aeronautics. However, the information will
also be of interest to the flying sports disc community."
http://www.disc-wing.com/
I hope these resources fully answer your question.
Sincerely,
mvguy
Google search term: aerodynamics frisbee
://www.google.com/search?q=aerodynamics+frisbee |
