AES wrote:
Just got our dog a new frisbee (he goes thru 'em pretty fast if we're
careless and leave them within reach after a session).

This one has a large outer wire rim, small inner ring, and stretched
radially between these 8 or 10 tapered spandex wedges (i.e., these
wedges get wider as they go radially outward). There are gaps of
comparable width between each of these blades, and each wedge is twisted
by 180 degrees between inner and outer rings with most of the twist
occurring close to the inner ring, so that these wedges give a
reasonably convincing imitation of a multi-bladed propellor.

This thing seems to fly just about as well, however, whether you fly it
right side up or upside down, and whether you flip it to spin CW or CCW.
(Hurts my left arm when I try to spin it CCW, however.) In other words,
if there's any helicopter effect here, it's pretty weak.

So, how does a frisbee fly, anyway? Another of his favorites is just a
10" diameter weighted outer rim filled in with a slightly saggy "cloth
drumhead", which visibly bulges upward 1" or so at the center into a
fair imitation of an airfoil when you throw it. I've always figured the
heavy rim kept the thing spinning and thus semi-rigid, and the forward
motion of the airfoil shape gave the lift.

I'm not 100% sure and I'm not aerodynamicist, but I think two things
help a frisbee fly, or any disk even one lacking an airfoil shape.

1. The gyroscopic stabilization provided by the spinning imparted when
thrown. Just try to throw a frisbee or any disk without spinning it.
It won't go anywhere.

2. A small AOA imparted also when thrown. This is the essential part
and (1) above is really only important to the extent that it allows the
angle of attack to be maintained during flight.

Almost any object will create lift if it has some AOA. You can verify
this by extending your hand out of the car window when driving, which
most of us did as kids. If you rotate your hand from horizontal to say
30 degrees relative to the wind, you can create a fair bit of lift. And
most of our hands aren't exactly an ideal airfoil.


Matt